9 ms·

Human body temperature has decreased in United States, study finds

111 points by elorant 7y ago

dorfsmay 7y ago
Completely unscientific observation: When working in offices, I have noticed that people who drink pop/soda daily prefer lower room temperature than people not consuming them at all. I might have "noticed" it because of a bunch of biases, but I'd love to see a proper study on that.
flyingfences 7y ago
Previous HN discussion: https://news.ycombinator.com/item?id=22002734 https://news.ycombinator.com/item?id=22002734
swebs 7y ago
>The decrease in average body temperature in the United States could be explained by a reduction in metabolic rate, or the amount of energy being used. The authors hypothesize that this reduction may be due to a population-wide decline in inflammation Let's not ignore the elephant in the room. A sedentary lifestyle with minimal exercise has become the norm.
- jriri93 7y ago
  Which is a relatively recent thing. How does that explain the trend going back as far as the article calls out? Without facts to back it, you’re projecting an emotional bias. Either anon commenter is a self loathing obese person or pointlessly finds obese people disgusting. Either way you’ve shown your opinions aren’t worth much
  - swebs 7y ago
    You can be sedentary and not obese, as long as you don't consume more calories than you spend.
- Ericson2314 7y ago
  Constant inflammation seems bad though? Isn't that one of the hypothesized downsides of too little fibre -> gut bacteria mildly but chronically attack instestinal wall?
- keymone 7y ago
  Hmm.. I find it hard to reconcile with the fact that obesity is so widespread I the US. Isn’t obesity linked to inflammation through (at least partially) insulin, which is quite inflammatory? Don’t have medical education, so maybe somebody could chime in.
  - hwillis 7y ago
    This study is comparing now to the early 1900s, when Aspirin was just starting to take off. Selection bias probably plays a very large part; they may have been able to measure temperatures but I doubt they were rigorous about taking representative cross-sections in 1910. Additionally the bias towards obesity has roughly switched- wealthier people were more likely to be obese in the 1900s, and now poorer people are more likely to be obese. Given that the people involved are in their 20s I would guess that obesity plays less of a role than you'd expect. [1]: https://en.wikipedia.org/wiki/Obesity_in_the_United_States#/media/File:Adult_male_obesity_in_the_United_States.svg https://en.wikipedia.org/wiki/Obesity_in_the_United_States#/...
- yk 7y ago
  That seems pretty straight forward to measure, you just take the temperature of people who exercise regularly (say three times a week) and compare that to people who work physically demanding jobs, and to people who work in office jobs, and don't exercise. (I would almost expect, that the study authors know of something like that, and would have mentioned it, if it were the case.)
  - swsieber 7y ago
    I would have expected it to be explicitly mentioned if considered.
  - dangerboysteve 7y ago
    I imagine apple has this data already with their apple watch data collections.
    - LeSaucy 7y ago
      There is no body temperature measurements in Apple Health from the Apple Watch, but that would definitely be an interesting data point were it available.
      - jjeaff 7y ago
        Yes, but also a potential privacy concern since if you have temperature data for a female, you could use it to pinpoint when ovulation may be occurring. I can only imagine that due to some of the recent privacy issues with cycle tracker apps that information might already be exploited for some nefarious advertising campaign.
  - NeuNeurosis 7y ago
    While we don't consider that sedentary, compared to the physical nature of the majority of jobs and lives these people would still be considered sedentary. I think a better comparison would be people who are doing long distance through hikes since their time under tension is extensive and the large distances they travel each while under load would be more respective of per-industrial lifestyles.
- nugget 7y ago
  Body temperature tends to decrease because of a deficiency in thyroid hormone also. Many of the synthetic chemicals used to treat modern day home goods seem to impact this system. I'd be curious whether there is any correlation there.
  - mordymoop 7y ago
    We also eat less animal thyroid.
    - elric 7y ago
      Are you referring to the actual organ? How was that eaten? And which animals? I enjoy weird foods, but I can't say I've ever seen thyroid on a menu.
      - kevin_thibedeau 7y ago
        The generic term in sweetbread, though it covers a variety of organs. https://en.wikipedia.org/wiki/Sweetbread https://en.wikipedia.org/wiki/Sweetbread
        diag 7y ago
        That would be thymus, not thyroid. Those are pretty different glands.
        phonypc 7y ago
        The thymus is not the thyroid gland, if that's the connection you're trying to make. AFAIK the thyroid gland is not deliberately consumed unless as medicine.
- tempsy 7y ago
  Low inflammation is a good thing, and never heard of a correlation between being sedentary and low inflammation.
  - naravara 7y ago
    If anything I've heard the correlation goes the other way. Regular exercise reduces inflammation markers across the board. Some people suggest it even helps alleviate allergy symptoms all else being equal.
    - soperj 7y ago
      I've exercised my entire life, regularly at a high level, and my allergy to cats developed when I was 10 and has only gotten progressively worse over the years. Started with just itchy eyes and skin and is now into full blown allergy induced asthma. I tell almost immediately when I'm in a house that has had a cat in the last few years. It's terrible. One data point and all...
      - RandomTisk 7y ago
        Most people can build up a tolerance. I grew up with cats close to home and never noticed any allergy as a kid. When I got my own indoor cat though, I noticed itching and then flu-like symptoms that got progressively worse. Allergy medication completely relieved all symptoms, and rather than get rid of fluffy I took allergy meds daily for about 2 weeks, then every second ord third day for another month. Now I'm pretty much free of symptoms, but I occasionally pop a pill if the roof my mouth or hands start to itch for any reason.
        soperj 7y ago
        I dated a girl for a while who owned a cat. I built up a tolerance to her cat (because she'd have the dander on her clothes), but it didn't help with any other cats. I was also still allergic to her cat, but it was at the point where a claritin would help. Mostly it's within half an hour I can barely breath, so it's hard to build up any sort of tolerance, even with allergy meds. Now it's easier for me to avoid cats entirely.
- adaisadais 7y ago
  Could this also possibly do to an increasing rate of global temperatures? One would think we would simply evolve towards a lower body temp in order to survive in a warm world.
  - ryanmercer 7y ago
    You're being downvoted but I can certainly see why someone might make this mental leap. Instead of downvoting you and driving along without comment let's think about this. CO2 levels for example can negatively impact cognitive function [1], perhaps this could have some impact on energy expenditure in the brain which might reduce body temperature some. Bodies will absolutely adjust to temperature changes as well (to some extent). Plausible but probably not a large percentage of a body temperature. I could see people being exposed to higher CO2 levels though due to the fact there are more and more indoor jobs, and less due to climate change. Even with HVAC systems, a quick Google query makes it seem that CO2 levels are generally higher in offices than outside [2] [3] [4] [5]. And while we're on that brain line of thinking... perhaps the increased consumption of television and mindless scrolling of social media feeds also results in far lower cognitive engagement which also decreases energy expenditure shrugs. Also worth looking at I suspect. For me I immediately thought of the thermic effect of food. Legumes, many spices, nuts, seeds etc all tend to have higher thermic effects. Perhaps eating a highly refined carbohydrate diet has caused a lowering in body temerapture by having lower thermic effects (I don't know, this was just my first mental leap). I suspect there is something here but probably not a major percentage of the difference. [1] = https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037 https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037 [2] - https://www.businessinsider.com/office-air-co2-levels-making-workers-tired-2017-11 https://www.businessinsider.com/office-air-co2-levels-making... [3] - https://www.ncbi.nlm.nih.gov/pubmed/26273786 https://www.ncbi.nlm.nih.gov/pubmed/26273786 [4] - https://www.planteriagroup.com/blog/co2-levels-in-offices-are-damaging-uk-productivity/63 https://www.planteriagroup.com/blog/co2-levels-in-offices-ar... [5] - https://www.washingtonpost.com/news/energy-environment/wp/2015/10/27/why-your-office-air-could-be-crimping-your-productivity/ https://www.washingtonpost.com/news/energy-environment/wp/20...
    - hwillis 7y ago
- Spooky23 7y ago
  I’d say the bigger elephant in the room is that thermometers have moved from an accurate standard (Mercury glass thermometers) to a hodge podge of alternatives. Some of these alternatives, like temporal scan thermometers vary dramatically.
- bstar77 7y ago
  As an adult, my body temp has always been low, around 97.2*. I also never get fevers. I'm also very athletic- I bike 3-4 times a week. Maybe there is a correlation with sedentary life, but I don't think it's a factor in my case nor many others.
  - hwillis 7y ago
    People who exercise have lower temperatures during sleep, similar or higher temperatures otherwise, and the same maximum temperature, which occurs during the evening. http://www.altmedrev.com/archive/publications/11/4/278.pdf http://www.altmedrev.com/archive/publications/11/4/278.pdf
- hwillis 7y ago
  > A sedentary lifestyle with minimal exercise has become the norm. The people being studied were in their 20s- obesity has increased 4-5x among children since 1980, but it's still only 20-25% for people in their 20s. Since then we've gotten gym class and advil- they had barely gotten aspirin. Selection bias probably plays a very large part. They may have been able to measure temperatures but I doubt they were rigorous about taking representative cross-sections in 1910. Additionally the bias towards obesity has roughly switched- wealthier people were more likely to be obese in the 1900s, and now poorer people are more likely to be obese. That said, muscle mass correlates almost directly with energy consumption. Muscles literally require energy to stay limp. Rigor mortis is caused by the supply of energy being cut off. The majority of the body's energy requirement is spent just keeping your muscles in working order- not even moving.
- chiefalchemist 7y ago
  My first reaction was to agree. However, if exercise ultimately makes the body more efficient, wouldn't that drop your body temp as your heart is beating less. That aside, the brain burns a significant percentage of calories burned. Perhaps on whole we are thinking less?
  - hwillis 7y ago
    People who exercise have lower temperatures during sleep, similar or higher temperatures otherwise, and the same maximum temperature, which occurs during the evening. http://www.altmedrev.com/archive/publications/11/4/278.pdf http://www.altmedrev.com/archive/publications/11/4/278.pdf
    - chiefalchemist 7y ago
      So it's a wash then. Correct? Which leaves the possibility of less it being a brain issue. Lower temps means less calories burned. There are many ways to accomplish that. Whatever happen to HN being a space where a legit "what if?" was explored, not knocked?
      - hwillis 7y ago
        It's almost certainly not a wash, unless all of the people in the records are having their temperatures taken while they sleep. People who are physically fit will tend to have very slightly higher body temperatures (less than what was found in the OP) when measured.
- koheripbal 7y ago
  Additionally, adipose tissue (fat) is slightly colder than internal tissue. The more fat content you have, the lower your average body temperature.
- ljm 7y ago
  Isn't the real elephant in the room obesity? And a culture around lifestyle and low-quality food that actively promotes it? If you're sitting on your ass all day and then going out to drink a gallon of HFCS-infused coke (free refills) and a low-budget meal that could satisfy a starving family, of course you're gonna get to this point. My personal thought with the US is "why does everything have to be so big?"
- readhn 7y ago
  > Let's not ignore the elephant in the room. A sedentary lifestyle with minimal exercise has become the norm. Huh? fitness industry is booming! Gym attendance is near all time highs! More and more people are eating healthier and switch to healthier and more active lifestyle.
  - gbear605 7y ago
    Assuming this wasn’t satirical, but it’s hard to tell sometimes. The rates of intentional exercise - going to a gym and working out - are certainly on the rise, but the actual rate of exercise is more lower than it was a hundred years ago. The job market has switched in large part to sedentary jobs from active jobs. And diets are much less healthy today than they were then because the only diets available (to anyone other than the rich) were relatively healthy. It’s hard to become overweight without the presence of junk food. Not impossible, certainly, but hard.
- JamesBarney 7y ago
  Sure I guess people in the 1800's who worked on farms were far less sedentary but my parents, and my grandparents and my great grandparents all worked jobs fairly similar to mine and drove to work. And none of them went to the gym like my generation (born in the 80's).
  - Broken_Hippo 7y ago
    I think that by the time we get to great grandparents, they did get more exercise. Sure, they might have been able to afford a single car, but lots of living had more activity. Housework, for example, took way more work while our great grandparents were young adults and children. Cars themselves were harder to drive with no power steering or brakes (and the early power-assists were very poor by today's standards). Office jobs had a lot more 'work' by their very nature simply because everything was on paper - there is a lot of little back and forth walking, bending, and lifting there. As children, they would have played outside lots and helped around the house (since house chores were more work). I think there were a lot of these little things that mean that yes, our 'sedentary' grandparents and great-grandparents were a lot more active just because of how life was.
BoiledCabbage 7y ago
So the summary is they aren't certain why, but it seems like it's due to people being a lot more sedentary, having lower metabolisms and being in climate controlled buildings a lot more. Unfortunately, it seems pretty predictable given the changes in our lifestyles...
- plopz 7y ago
  Why is it unfortunate? The article didn't seem to say whether this change was good or bad, although I would assume a decrease in inflammation would be good?
  - kempbellt 7y ago
    > I would assume a decrease in inflammation would be good I'd be careful with that assumption. Context means everything. It depends on what caused the inflammation, and what is causing its decrease.
    - jonas21 7y ago
      Here's the relevant context from the study: > Economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age together are likely to have decreased chronic inflammation since the 19th century. For example, in the mid-19th century, 2–3% of the population would have been living with active tuberculosis (Tiemersma et al., 2011). This figure is consistent with the UAVCW Surgeons' Certificates that reported 737 cases of active tuberculosis among 23,757 subjects (3.1%). That UAVCW veterans who reported either current tuberculosis or pneumonia had a higher temperature (0.19°C and 0.03°C respectively) than those without infectious conditions supports this theory. I would assume that less tuberculosis is a good thing (though, this being Hacker News, someone will probably show up to question that assumption too).
      - kempbellt 7y ago
        Inflammation is one of the body's natural defense mechanisms to issues like infection, or injury. Treating inflammation like it is the "bad thing", while ignoring (or not understanding) the underlying cause of it is not good, and potentially hazardous. People do this all the time by taking ibuprofen to treat headaches or minor pains that are natural indicators that something is wrong (dehydration, infection, etc). Tuberculosis is a disease, and widely accepted as detrimental to human health. I agree, less tuberculosis = a good thing. This being a medically related post, more information, and less assumptions is better for everyone. Thank you for adding context.
idclip 7y ago
We are a snake world after all! Damnit morty! Ssssssssssssss (I welcome the downvotes! Ssssssss)
moralsupply 7y ago
This has obviously been planned by the cold-blooded Reptilians
jriri93 7y ago
The warming effects of carbon emissions on the atmosphere was scientifically known and measured back in the 1800s. Seems reasonable that as the climate warmed by fractions, we cooled by fractions.
- chrisco255 7y ago
  Uh, you know people who live in the northern part of the United States experience temps that are on average 10-20 degrees cooler than the southern part of the United States? If what you said were true we would notice a latitudinal difference in body temps. But we don't. In fact many parts of the U.S. have cooled on average in the past couple decades.
  - cujo 7y ago
    Do you have some data on this?
    - hwillis 7y ago
      It's false[1]; everywhere in the US is 2-4 F warmer than it was prior to 2000. He may have this impression from looking at 2002, which was a particularly warm year. Some parts of the midwest have been cooler than they were in 2002. The general thing about the person he was responding to being totally wrong was obviously correct. [1]: https://climate.nasa.gov/vital-signs/global-temperature/ https://climate.nasa.gov/vital-signs/global-temperature/
      - chrisco255 7y ago
        From your link the baseline average is from "relative to 1951-1980 average". Which was the coldest period of the 20th century. It got so cold in the 70s they were predicting an incoming ice age. It's very dishonest and very wrong to cherry pick the coldest modern period of temperature and then say we have increased by 0.8C from there. Climate is cyclical and there are many Multi-decadal Oscillations in oceans that impact global temperature, rainfall patterns, and overall climate conditions. The AMO, the PDO, not to mention ENSO. As far as anamolies go, which area is experiencing "cooler than average" (which, as mentioned above, is difficult to do) depends on the year, but here's a map from NOAA showing 2013 temps and clearly shows the Western U.S. experiencing below average temps (from a 1980-2010 baseline): https://www.ncdc.noaa.gov/sotc/service/global/map-blended-mntp/201301.gif https://www.ncdc.noaa.gov/sotc/service/global/map-blended-mn... And to underscore the situation in the 1970s I'm going to link to a documentary that starred Leonard Nemoy as narrator in 1978. Quotes below and link below to clips from: “In Search of…The Coming Ice Age”, narrated by Leonard Nimoy (Spock from Star Trek): “…sea coasts long free of summer ice, are now blocked year round…” “…the data shows temperatures in the arctic have fallen dramatically over the last 30 years…” “…in most locations the drop has been about 2 degrees Centigrade…” https://youtu.be/1kGB5MMIAVA https://youtu.be/1kGB5MMIAVA https://youtu.be/mOC7ePWCHGk https://youtu.be/mOC7ePWCHGk GISS also claims to have global temperature data from 1884 that doesn't exist. They interpolate and make up numbers when they go back that far, as we don't have records from much of Asia, Africa, eastern Europe and south America during that time, even huge swaths of Australia were not covered by temperature gauges. We didn't really start getting quality global temperature data until the satellite era.
trhway 7y ago
i'd guess that given the antibiotics, better nutrition, wide availability of warm clothes/shoes, etc. natural selection pressure for higher temperature has naturally decreased (in such historically short period that decrease mostly manifested itself in much lower child mortality). People also became bigger during the last century which results in better thermodynamics, ie. surface/volume ratio, thus less need for burning of the internal fuel, i.e metabolic rate can be lower. Compare - elephant's 96.6 vs. cat's 101.5 body temp.
deleted 7y ago
[deleted]
dmitryminkovsky 7y ago
No mention of high prevalence of cold beverage and ice consumption. Couldn’t possibly be related?
- yakshaving_jgt 7y ago
  I don’t think that’s how the human body works.
danbr 7y ago
WSJ article referencing this research: https://www.wsj.com/articles/98-6-degrees-fahrenheit-isnt-the-average-any-more-11579257001 https://www.wsj.com/articles/98-6-degrees-fahrenheit-isnt-th...
mechhacker 7y ago
The original average was set in 1868. Isn't it likely that this is just a measurement/calibration/methodology error?
- pseudoramble 7y ago
  They do mention this in the article: > As part of the study, the authors investigated the possibility that the decrease could simply reflect improvements in thermometer technology; thermometers used today are far more accurate than those used two centuries ago. “In the 19thcentury, thermometry was just beginning,” Parsonnet said. > To assess whether temperatures truly decreased, the researchers checked for body temperature trends within each dataset; for each historical group, they expected that measurements would be taken with similar thermometers. Within the veterans dataset, they observed a similar decrease for each decade, consistent with observations made using the combined data.
  - mikedilger 7y ago
    I'm unconvinced by their method to assess whether temperatures truly decreased. Why wouldn't a methodological error not also apply to the veterans dataset? E.g. all thermometers of an era reading slightly hot (rather than them all being less accurate in any direction)
    - pseudoramble 7y ago
      Yeah, fair point! I'm not well versed in this kind of stuff. So I'm not sure. Maybe the original paper discusses the point though? Perhaps they have a way to normalize temperatures to a baseline across all data sets and evaluate that way.
juskrey 7y ago
Just look inside any US pharmacy
- freeone3000 7y ago
  For what, exactly?
  - hoka-one-one 7y ago
    Love
deleted 7y ago
[deleted]
nostrademons 7y ago
Interesting. 100F is supposed to be normal human body temperature, by definition. (Fahrenheit set 100F as normal human body temperature and 0 as the coldest temperature he could achieve, using a mixture of ice, water, and ammonium chloride.) For years I'd heard that the reason normal body temperature is 98.6 is because Fahrenheit was running a slight fever at the time he made his scale, but this article suggests that it might've been accurate, but body temperature has been decreasing. If you extrapolate the numbers in the article out (a drop of just over a degree since the 1800s) to when Fahrenheit made his scale in 1724, it's possible that normal body temperature actually was very close to 100F then.
- jefftk 7y ago
  Thermometers weren't very accurate initially, and the scales were defined multiple times in the early years. Here's what Wikipedia has on this: According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[10] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power). Fahrenheit soon after observed that water boils at about 212 degrees using this scale. The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98.2° (sic) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale). https://en.wikipedia.org/wiki/Fahrenheit#History https://en.wikipedia.org/wiki/Fahrenheit#History
- DenisM 7y ago
cheschire 7y ago
I would love to see some research that attempts to correlate this to other species that have local declines in birth rate. Maybe it’s a mammalian response to over population.
- hwillis 7y ago
  No, that's silly. Unless mammals are magic, the only way a species could possibly know about population is by the number of individuals it sees locally, and the number they see. That would cause there to be a huge and noticeable difference between eg rural and urban populations.
  - cheschire 7y ago
    Well, I didn't write an entire introduction paragraph for a research paper, sure, but outright dismissing as "silly" seems rather closed minded.
CamelCaseName 7y ago
I found this passage interesting (about the impact of climate controlled environments on resting metabolic rate) > Changes in ambient temperature may also explain some of the observed change in body temperature over time. Maintaining constant body temperature despite fluctuations in ambient temperature consumes up to 50–70% of daily energy intake (Levine, 2007). > Resting metabolic rate (RMR), for which body temperature is a crude proxy, increases when the ambient temperature decreases below or rises above the thermoneutral zone, that is the temperature of the environment at which humans can maintain normal temperature with minimum energy expenditure (Erikson et al., 1956). > ... Thus, the amount of time the population has spent at thermoneutral zones has markedly increased, potentially causing a decrease in RMR, and, by analogy, body temperature. Source: https://elifesciences.org/articles/49555 https://elifesciences.org/articles/49555
rhacker 7y ago
I wonder if they simply looked at the antibiotic use. For example when that was introduced specifically, and more so when we started "over-prescribing" it. That's got to have had an effect of persistent low grade fevers that exist in just about everyone.
- hwillis 7y ago
  Body temperatures are currently lower, so the opposite of what you're suggesting with low grade fevers from overprescription of antibiotics. However, fevers are caused by a subset of the interleukin family, which as a whole causes inflammation. Inflammation was the author's suggestion. Also, low grade fevers aren't a thing. Fever is caused by the immune system. You can only have a continuous infection with diseases that avoid or supress the immune system. There are a small number of brain-affecting infectious diseases like meningitis that can raise body temperature on their own. Chronically recurring stuff will also give you intermittent fevers, but there's no low-grade. You have it or you don't.
deleted 7y ago
[deleted]
mattkrause 7y ago
Link to the actual study: https://elifesciences.org/articles/49555 https://elifesciences.org/articles/49555 Protsiv, M., Ley, C., Lankester, J., Hastie, T., & Parsonnet, J. (2020). Decreasing human body temperature in the United States since the industrial revolution. eLife, 9, e49555.
hopia 7y ago
The latest temperature data was measured from patients visiting hospital. Older people are naturally more prone to health problems and would therefore be visiting hospital more than younger people, on average. Our average lifespan is longer than it used to be. I'd assume older people have a lower base temperature. This would skew the results statistically.
- RhodesianHunter 7y ago
  I would assume that a well constructed study would account for this.
  - hopia 7y ago
    Yes, I have to admit I haven't read the actual study so this was purely speculation.
  - cosmotic 7y ago
    In my experience, studies are typically not well constructed. See the numerous studies that cannot be replicated, the below-the-surface iceberg of unpublished (unfavorable) studies paid for by for-profit institutions, or the shockingly small sample set or biased sample set in most studies. Most studies expose this information implicitly but it's up to the reader to determine the bias or replicate the study.
    - hwillis 7y ago
      The study compared people born after 1990, so if there were any old people in that cohort this study would be much bigger news.
- hwillis 7y ago
  The study compared people born after 1990, so if there were any old people in that cohort this study would be much bigger news.
therealx 7y ago
I've noticed that my temp is always 1 degree lower than it should be. It's never been a problem and has been that way since birth.
- hwillis 7y ago
  The normal range of resting body temperatures is anywhere from 95 to 100 F. People vary a lot.
pandaman 7y ago
I was always confused how 37 C was a normal temperature in the US. In the USSR where I grew it was a fever and the normal was 36.6. Could it be the way it's measured?
- comicjk 7y ago
  Temperatures of 37 C and 36.6 C are barely distinguishable with an ordinary thermometer, and both are within the normal range of human body temperatures (37.32-38.76 C). www.ncbi.nlm.nih.gov/pmc/articles/PMC6456186
- elric 7y ago
  Not sure about any US/USSR differences, but there can be pretty big differences between people individually, between measurements in the same person throughout the day (or month for women), and between how it's measured. 37°C is an average. Axillary (armpit) measurements, for example, are a lot colder than oral or rectal measurements. Perhaps the Russians favoured the former, while the Americans preferred the latter? I suspect there's a nice little bell curve with 37°C in the middle.
  - pandaman 7y ago
    Yes, Russia measures temperature in the armpit. Is it really that much colder than in the mouth? Edit: A 37 temperature would automatically give you an excuse from school when I was a kid and, obviously, children always were finding ways to cheat. If just putting the thermometer in your mouth worked then either I was in the dark or nobody has discovered this.
    - elric 7y ago
      Yes, the armpit is roughly 0.5°C colder than the mouth.
ZeroFries 7y ago
When I shovel the driveway, I'm sweating wearing no jacket, but I freeze sitting on the porch in a parka.
- deleted 7y ago
  [deleted]
bobloblaw45 7y ago
I'm leaning strongly on the side of thermometers were less accurate and gave a higher reading in the early 1800s.
- hwillis 7y ago
  The study was on measurements taken in the early 1900s, not 1800s. Also, it's not like technology suddenly started in the 30s or something. Liquid nitrogen was first produced in 1883. The periodic table was published in 1869. Cells were discovered in 1665. Science was a lot more than banging rocks together. You would expect the opposite of what you're suggesting, if anything. If water was used for calibrating temperature then there would be fewer good ways to control the impurity level, which would lower its freezing point. Not to mention Fahrenheit originally defined body temperature as 96 F, and it was later corrected higher. All of the above is totally moot because we have plenty of medical thermometers from the 1900s and earlier, and they are remarkably accurate and the error is not particularly biased in either way. This is a highly researched area because the accuracy of whether thermometers is important to historical and climate research. Medical thermometers from the 1800s are good to at least 1/5th of a degree and instrumentation thermometers were good to hundredths.
redwood 7y ago
Seems conceivable that higher proportion of body fat aka more insulation could also contribute
- hwillis 7y ago
  Fat would do the opposite. The core body temperature would be the same, because otherwise it would be too hot. The distal body temperature would be insulated from the sources of heat, so the inside of your mouth, forehead, rectum etc would be cooler.
julius_set 7y ago
I’m not sure how much this matters but I’ve been on TRT therapy for a while now and I remember before I started my limbs would get so cold, and hands would be so cold to touch. After therapy my significant other tells me I’m like a body heater constantly radiating heat possibly due to high synthesis and metabolism. I’m curious but there was a chart I saw as well regarding men’s testosterone levels declining over the last century I wonder how related that is to lowered body temperatures
mrfusion 7y ago
This could simply be a result of nationwide iodine deficiency. Our main source is fortified salt and everyone is cutting back on their sodium or using fancier salts that don’t add iodine. I make sure to put a pinch of iodized salt in everything I cook.
- hwillis 7y ago
  This study is from before iodine was added supplementally (1924 in the US). You are correct that iodine deficiency leads to low body temperature due to hyperthyroidism. Dairy and grain are the biggest sources of iodine. To get your iodine from salt alone would require over 3 grams per day, which is quite a lot. The average American consumes 3.4 g, DV recommendation is 2.3 g.
pattusk 7y ago
Could some of it be explained by demographic changes (immigration)? iI remember always being taught growing up than 37.5°C was the average human body temperature. However after moving to East Asia I met plenty of people who consider 37.5 a light fever and 36 the normal temp. On my phone so no data to back it up for now though...
jl2718 7y ago
A lot of comments here blame obesity/sedentary lifestyles/junk food for low body temperature. Let’s look at this: Obesity: raises temperature exercise: lowers resting temperature junk food: raises temperature What if it’s the reverse? What if your desire to eat and not exercise had a lot to do with being cold? Frankly I’m not buying the arguments in the article. Occam’s razor says it’s a common nutritional deficiency or environmental toxin affecting the thyroid.
- jl2718 7y ago
  Anecdote: I’ve been getting noticeably colder every year for no natural reason, so I’ve tried many things: fish oil, iodine etc. The only thing that worked was iron. I took 600mg ferrous gluconate with 5g vitamin C, and I was sweating hot and felt amazing for the next 24 hours. Iron overdose can be deadly and irreversible, so I have not repeated this and do not recommend it.

111 points by elorant 7y ago

Completely unscientific observation: When working in offices, I have noticed that people who drink pop/soda daily prefer lower room temperature than people not consuming them at all. I might have "noticed" it because of a bunch of biases, but I'd love to see a proper study on that.

flyingfences 7y ago

Previous HN discussion: https://news.ycombinator.com/item?id=22002734 https://news.ycombinator.com/item?id=22002734

swebs 7y ago

>The decrease in average body temperature in the United States could be explained by a reduction in metabolic rate, or the amount of energy being used. The authors hypothesize that this reduction may be due to a population-wide decline in inflammation Let's not ignore the elephant in the room. A sedentary lifestyle with minimal exercise has become the norm.

jriri93 7y ago
Which is a relatively recent thing. How does that explain the trend going back as far as the article calls out? Without facts to back it, you’re projecting an emotional bias. Either anon commenter is a self loathing obese person or pointlessly finds obese people disgusting. Either way you’ve shown your opinions aren’t worth much
- swebs 7y ago
  You can be sedentary and not obese, as long as you don't consume more calories than you spend.
Ericson2314 7y ago
Constant inflammation seems bad though? Isn't that one of the hypothesized downsides of too little fibre -> gut bacteria mildly but chronically attack instestinal wall?
keymone 7y ago
Hmm.. I find it hard to reconcile with the fact that obesity is so widespread I the US. Isn’t obesity linked to inflammation through (at least partially) insulin, which is quite inflammatory? Don’t have medical education, so maybe somebody could chime in.
- hwillis 7y ago
  This study is comparing now to the early 1900s, when Aspirin was just starting to take off. Selection bias probably plays a very large part; they may have been able to measure temperatures but I doubt they were rigorous about taking representative cross-sections in 1910. Additionally the bias towards obesity has roughly switched- wealthier people were more likely to be obese in the 1900s, and now poorer people are more likely to be obese. Given that the people involved are in their 20s I would guess that obesity plays less of a role than you'd expect. [1]: https://en.wikipedia.org/wiki/Obesity_in_the_United_States#/media/File:Adult_male_obesity_in_the_United_States.svg https://en.wikipedia.org/wiki/Obesity_in_the_United_States#/...
yk 7y ago
That seems pretty straight forward to measure, you just take the temperature of people who exercise regularly (say three times a week) and compare that to people who work physically demanding jobs, and to people who work in office jobs, and don't exercise. (I would almost expect, that the study authors know of something like that, and would have mentioned it, if it were the case.)
- swsieber 7y ago
  I would have expected it to be explicitly mentioned if considered.
- dangerboysteve 7y ago
  I imagine apple has this data already with their apple watch data collections.
  - LeSaucy 7y ago
    There is no body temperature measurements in Apple Health from the Apple Watch, but that would definitely be an interesting data point were it available.
    - jjeaff 7y ago
      Yes, but also a potential privacy concern since if you have temperature data for a female, you could use it to pinpoint when ovulation may be occurring. I can only imagine that due to some of the recent privacy issues with cycle tracker apps that information might already be exploited for some nefarious advertising campaign.
- NeuNeurosis 7y ago
  While we don't consider that sedentary, compared to the physical nature of the majority of jobs and lives these people would still be considered sedentary. I think a better comparison would be people who are doing long distance through hikes since their time under tension is extensive and the large distances they travel each while under load would be more respective of per-industrial lifestyles.
nugget 7y ago
Body temperature tends to decrease because of a deficiency in thyroid hormone also. Many of the synthetic chemicals used to treat modern day home goods seem to impact this system. I'd be curious whether there is any correlation there.
- mordymoop 7y ago
  We also eat less animal thyroid.
  - elric 7y ago
    Are you referring to the actual organ? How was that eaten? And which animals? I enjoy weird foods, but I can't say I've ever seen thyroid on a menu.
    - kevin_thibedeau 7y ago
      The generic term in sweetbread, though it covers a variety of organs. https://en.wikipedia.org/wiki/Sweetbread https://en.wikipedia.org/wiki/Sweetbread
      - diag 7y ago
        That would be thymus, not thyroid. Those are pretty different glands.
      - phonypc 7y ago
        The thymus is not the thyroid gland, if that's the connection you're trying to make. AFAIK the thyroid gland is not deliberately consumed unless as medicine.
tempsy 7y ago
Low inflammation is a good thing, and never heard of a correlation between being sedentary and low inflammation.
- naravara 7y ago
  If anything I've heard the correlation goes the other way. Regular exercise reduces inflammation markers across the board. Some people suggest it even helps alleviate allergy symptoms all else being equal.
  - soperj 7y ago
    I've exercised my entire life, regularly at a high level, and my allergy to cats developed when I was 10 and has only gotten progressively worse over the years. Started with just itchy eyes and skin and is now into full blown allergy induced asthma. I tell almost immediately when I'm in a house that has had a cat in the last few years. It's terrible. One data point and all...
    - RandomTisk 7y ago
      Most people can build up a tolerance. I grew up with cats close to home and never noticed any allergy as a kid. When I got my own indoor cat though, I noticed itching and then flu-like symptoms that got progressively worse. Allergy medication completely relieved all symptoms, and rather than get rid of fluffy I took allergy meds daily for about 2 weeks, then every second ord third day for another month. Now I'm pretty much free of symptoms, but I occasionally pop a pill if the roof my mouth or hands start to itch for any reason.
      - soperj 7y ago
        I dated a girl for a while who owned a cat. I built up a tolerance to her cat (because she'd have the dander on her clothes), but it didn't help with any other cats. I was also still allergic to her cat, but it was at the point where a claritin would help. Mostly it's within half an hour I can barely breath, so it's hard to build up any sort of tolerance, even with allergy meds. Now it's easier for me to avoid cats entirely.
adaisadais 7y ago
Could this also possibly do to an increasing rate of global temperatures? One would think we would simply evolve towards a lower body temp in order to survive in a warm world.
- ryanmercer 7y ago
  You're being downvoted but I can certainly see why someone might make this mental leap. Instead of downvoting you and driving along without comment let's think about this. CO2 levels for example can negatively impact cognitive function [1], perhaps this could have some impact on energy expenditure in the brain which might reduce body temperature some. Bodies will absolutely adjust to temperature changes as well (to some extent). Plausible but probably not a large percentage of a body temperature. I could see people being exposed to higher CO2 levels though due to the fact there are more and more indoor jobs, and less due to climate change. Even with HVAC systems, a quick Google query makes it seem that CO2 levels are generally higher in offices than outside [2] [3] [4] [5]. And while we're on that brain line of thinking... perhaps the increased consumption of television and mindless scrolling of social media feeds also results in far lower cognitive engagement which also decreases energy expenditure shrugs. Also worth looking at I suspect. For me I immediately thought of the thermic effect of food. Legumes, many spices, nuts, seeds etc all tend to have higher thermic effects. Perhaps eating a highly refined carbohydrate diet has caused a lowering in body temerapture by having lower thermic effects (I don't know, this was just my first mental leap). I suspect there is something here but probably not a major percentage of the difference. [1] = https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037 https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037 [2] - https://www.businessinsider.com/office-air-co2-levels-making-workers-tired-2017-11 https://www.businessinsider.com/office-air-co2-levels-making... [3] - https://www.ncbi.nlm.nih.gov/pubmed/26273786 https://www.ncbi.nlm.nih.gov/pubmed/26273786 [4] - https://www.planteriagroup.com/blog/co2-levels-in-offices-are-damaging-uk-productivity/63 https://www.planteriagroup.com/blog/co2-levels-in-offices-ar... [5] - https://www.washingtonpost.com/news/energy-environment/wp/2015/10/27/why-your-office-air-could-be-crimping-your-productivity/ https://www.washingtonpost.com/news/energy-environment/wp/20...
  - hwillis 7y ago
Spooky23 7y ago
I’d say the bigger elephant in the room is that thermometers have moved from an accurate standard (Mercury glass thermometers) to a hodge podge of alternatives. Some of these alternatives, like temporal scan thermometers vary dramatically.
bstar77 7y ago
As an adult, my body temp has always been low, around 97.2*. I also never get fevers. I'm also very athletic- I bike 3-4 times a week. Maybe there is a correlation with sedentary life, but I don't think it's a factor in my case nor many others.
- hwillis 7y ago
  People who exercise have lower temperatures during sleep, similar or higher temperatures otherwise, and the same maximum temperature, which occurs during the evening. http://www.altmedrev.com/archive/publications/11/4/278.pdf http://www.altmedrev.com/archive/publications/11/4/278.pdf
hwillis 7y ago
> A sedentary lifestyle with minimal exercise has become the norm. The people being studied were in their 20s- obesity has increased 4-5x among children since 1980, but it's still only 20-25% for people in their 20s. Since then we've gotten gym class and advil- they had barely gotten aspirin. Selection bias probably plays a very large part. They may have been able to measure temperatures but I doubt they were rigorous about taking representative cross-sections in 1910. Additionally the bias towards obesity has roughly switched- wealthier people were more likely to be obese in the 1900s, and now poorer people are more likely to be obese. That said, muscle mass correlates almost directly with energy consumption. Muscles literally require energy to stay limp. Rigor mortis is caused by the supply of energy being cut off. The majority of the body's energy requirement is spent just keeping your muscles in working order- not even moving.
chiefalchemist 7y ago
My first reaction was to agree. However, if exercise ultimately makes the body more efficient, wouldn't that drop your body temp as your heart is beating less. That aside, the brain burns a significant percentage of calories burned. Perhaps on whole we are thinking less?
- hwillis 7y ago
  People who exercise have lower temperatures during sleep, similar or higher temperatures otherwise, and the same maximum temperature, which occurs during the evening. http://www.altmedrev.com/archive/publications/11/4/278.pdf http://www.altmedrev.com/archive/publications/11/4/278.pdf
  - chiefalchemist 7y ago
    So it's a wash then. Correct? Which leaves the possibility of less it being a brain issue. Lower temps means less calories burned. There are many ways to accomplish that. Whatever happen to HN being a space where a legit "what if?" was explored, not knocked?
    - hwillis 7y ago
      It's almost certainly not a wash, unless all of the people in the records are having their temperatures taken while they sleep. People who are physically fit will tend to have very slightly higher body temperatures (less than what was found in the OP) when measured.
koheripbal 7y ago
Additionally, adipose tissue (fat) is slightly colder than internal tissue. The more fat content you have, the lower your average body temperature.
ljm 7y ago
Isn't the real elephant in the room obesity? And a culture around lifestyle and low-quality food that actively promotes it? If you're sitting on your ass all day and then going out to drink a gallon of HFCS-infused coke (free refills) and a low-budget meal that could satisfy a starving family, of course you're gonna get to this point. My personal thought with the US is "why does everything have to be so big?"
readhn 7y ago
> Let's not ignore the elephant in the room. A sedentary lifestyle with minimal exercise has become the norm. Huh? fitness industry is booming! Gym attendance is near all time highs! More and more people are eating healthier and switch to healthier and more active lifestyle.
- gbear605 7y ago
  Assuming this wasn’t satirical, but it’s hard to tell sometimes. The rates of intentional exercise - going to a gym and working out - are certainly on the rise, but the actual rate of exercise is more lower than it was a hundred years ago. The job market has switched in large part to sedentary jobs from active jobs. And diets are much less healthy today than they were then because the only diets available (to anyone other than the rich) were relatively healthy. It’s hard to become overweight without the presence of junk food. Not impossible, certainly, but hard.
JamesBarney 7y ago
Sure I guess people in the 1800's who worked on farms were far less sedentary but my parents, and my grandparents and my great grandparents all worked jobs fairly similar to mine and drove to work. And none of them went to the gym like my generation (born in the 80's).
- Broken_Hippo 7y ago
  I think that by the time we get to great grandparents, they did get more exercise. Sure, they might have been able to afford a single car, but lots of living had more activity. Housework, for example, took way more work while our great grandparents were young adults and children. Cars themselves were harder to drive with no power steering or brakes (and the early power-assists were very poor by today's standards). Office jobs had a lot more 'work' by their very nature simply because everything was on paper - there is a lot of little back and forth walking, bending, and lifting there. As children, they would have played outside lots and helped around the house (since house chores were more work). I think there were a lot of these little things that mean that yes, our 'sedentary' grandparents and great-grandparents were a lot more active just because of how life was.

BoiledCabbage 7y ago

So the summary is they aren't certain why, but it seems like it's due to people being a lot more sedentary, having lower metabolisms and being in climate controlled buildings a lot more. Unfortunately, it seems pretty predictable given the changes in our lifestyles...

plopz 7y ago
Why is it unfortunate? The article didn't seem to say whether this change was good or bad, although I would assume a decrease in inflammation would be good?
- kempbellt 7y ago
  > I would assume a decrease in inflammation would be good I'd be careful with that assumption. Context means everything. It depends on what caused the inflammation, and what is causing its decrease.
  - jonas21 7y ago
    Here's the relevant context from the study: > Economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age together are likely to have decreased chronic inflammation since the 19th century. For example, in the mid-19th century, 2–3% of the population would have been living with active tuberculosis (Tiemersma et al., 2011). This figure is consistent with the UAVCW Surgeons' Certificates that reported 737 cases of active tuberculosis among 23,757 subjects (3.1%). That UAVCW veterans who reported either current tuberculosis or pneumonia had a higher temperature (0.19°C and 0.03°C respectively) than those without infectious conditions supports this theory. I would assume that less tuberculosis is a good thing (though, this being Hacker News, someone will probably show up to question that assumption too).
    - kempbellt 7y ago
      Inflammation is one of the body's natural defense mechanisms to issues like infection, or injury. Treating inflammation like it is the "bad thing", while ignoring (or not understanding) the underlying cause of it is not good, and potentially hazardous. People do this all the time by taking ibuprofen to treat headaches or minor pains that are natural indicators that something is wrong (dehydration, infection, etc). Tuberculosis is a disease, and widely accepted as detrimental to human health. I agree, less tuberculosis = a good thing. This being a medically related post, more information, and less assumptions is better for everyone. Thank you for adding context.

idclip 7y ago

We are a snake world after all! Damnit morty! Ssssssssssssss (I welcome the downvotes! Ssssssss)

moralsupply 7y ago

This has obviously been planned by the cold-blooded Reptilians

jriri93 7y ago

The warming effects of carbon emissions on the atmosphere was scientifically known and measured back in the 1800s. Seems reasonable that as the climate warmed by fractions, we cooled by fractions.

chrisco255 7y ago
Uh, you know people who live in the northern part of the United States experience temps that are on average 10-20 degrees cooler than the southern part of the United States? If what you said were true we would notice a latitudinal difference in body temps. But we don't. In fact many parts of the U.S. have cooled on average in the past couple decades.
- cujo 7y ago
  Do you have some data on this?
  - hwillis 7y ago
    It's false[1]; everywhere in the US is 2-4 F warmer than it was prior to 2000. He may have this impression from looking at 2002, which was a particularly warm year. Some parts of the midwest have been cooler than they were in 2002. The general thing about the person he was responding to being totally wrong was obviously correct. [1]: https://climate.nasa.gov/vital-signs/global-temperature/ https://climate.nasa.gov/vital-signs/global-temperature/
    - chrisco255 7y ago
      From your link the baseline average is from "relative to 1951-1980 average". Which was the coldest period of the 20th century. It got so cold in the 70s they were predicting an incoming ice age. It's very dishonest and very wrong to cherry pick the coldest modern period of temperature and then say we have increased by 0.8C from there. Climate is cyclical and there are many Multi-decadal Oscillations in oceans that impact global temperature, rainfall patterns, and overall climate conditions. The AMO, the PDO, not to mention ENSO. As far as anamolies go, which area is experiencing "cooler than average" (which, as mentioned above, is difficult to do) depends on the year, but here's a map from NOAA showing 2013 temps and clearly shows the Western U.S. experiencing below average temps (from a 1980-2010 baseline): https://www.ncdc.noaa.gov/sotc/service/global/map-blended-mntp/201301.gif https://www.ncdc.noaa.gov/sotc/service/global/map-blended-mn... And to underscore the situation in the 1970s I'm going to link to a documentary that starred Leonard Nemoy as narrator in 1978. Quotes below and link below to clips from: “In Search of…The Coming Ice Age”, narrated by Leonard Nimoy (Spock from Star Trek): “…sea coasts long free of summer ice, are now blocked year round…” “…the data shows temperatures in the arctic have fallen dramatically over the last 30 years…” “…in most locations the drop has been about 2 degrees Centigrade…” https://youtu.be/1kGB5MMIAVA https://youtu.be/1kGB5MMIAVA https://youtu.be/mOC7ePWCHGk https://youtu.be/mOC7ePWCHGk GISS also claims to have global temperature data from 1884 that doesn't exist. They interpolate and make up numbers when they go back that far, as we don't have records from much of Asia, Africa, eastern Europe and south America during that time, even huge swaths of Australia were not covered by temperature gauges. We didn't really start getting quality global temperature data until the satellite era.

trhway 7y ago

i'd guess that given the antibiotics, better nutrition, wide availability of warm clothes/shoes, etc. natural selection pressure for higher temperature has naturally decreased (in such historically short period that decrease mostly manifested itself in much lower child mortality). People also became bigger during the last century which results in better thermodynamics, ie. surface/volume ratio, thus less need for burning of the internal fuel, i.e metabolic rate can be lower. Compare - elephant's 96.6 vs. cat's 101.5 body temp.

deleted 7y ago

[deleted]

dmitryminkovsky 7y ago

No mention of high prevalence of cold beverage and ice consumption. Couldn’t possibly be related?

yakshaving_jgt 7y ago
I don’t think that’s how the human body works.

danbr 7y ago

WSJ article referencing this research: https://www.wsj.com/articles/98-6-degrees-fahrenheit-isnt-the-average-any-more-11579257001 https://www.wsj.com/articles/98-6-degrees-fahrenheit-isnt-th...

mechhacker 7y ago

The original average was set in 1868. Isn't it likely that this is just a measurement/calibration/methodology error?

pseudoramble 7y ago
They do mention this in the article: > As part of the study, the authors investigated the possibility that the decrease could simply reflect improvements in thermometer technology; thermometers used today are far more accurate than those used two centuries ago. “In the 19thcentury, thermometry was just beginning,” Parsonnet said. > To assess whether temperatures truly decreased, the researchers checked for body temperature trends within each dataset; for each historical group, they expected that measurements would be taken with similar thermometers. Within the veterans dataset, they observed a similar decrease for each decade, consistent with observations made using the combined data.
- mikedilger 7y ago
  I'm unconvinced by their method to assess whether temperatures truly decreased. Why wouldn't a methodological error not also apply to the veterans dataset? E.g. all thermometers of an era reading slightly hot (rather than them all being less accurate in any direction)
  - pseudoramble 7y ago
    Yeah, fair point! I'm not well versed in this kind of stuff. So I'm not sure. Maybe the original paper discusses the point though? Perhaps they have a way to normalize temperatures to a baseline across all data sets and evaluate that way.

juskrey 7y ago

Just look inside any US pharmacy

freeone3000 7y ago
For what, exactly?
- hoka-one-one 7y ago
  Love

deleted 7y ago

[deleted]

nostrademons 7y ago

Interesting. 100F is supposed to be normal human body temperature, by definition. (Fahrenheit set 100F as normal human body temperature and 0 as the coldest temperature he could achieve, using a mixture of ice, water, and ammonium chloride.) For years I'd heard that the reason normal body temperature is 98.6 is because Fahrenheit was running a slight fever at the time he made his scale, but this article suggests that it might've been accurate, but body temperature has been decreasing. If you extrapolate the numbers in the article out (a drop of just over a degree since the 1800s) to when Fahrenheit made his scale in 1724, it's possible that normal body temperature actually was very close to 100F then.

jefftk 7y ago
Thermometers weren't very accurate initially, and the scales were defined multiple times in the early years. Here's what Wikipedia has on this: According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[10] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power). Fahrenheit soon after observed that water boils at about 212 degrees using this scale. The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98.2° (sic) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale). https://en.wikipedia.org/wiki/Fahrenheit#History https://en.wikipedia.org/wiki/Fahrenheit#History
DenisM 7y ago

cheschire 7y ago

I would love to see some research that attempts to correlate this to other species that have local declines in birth rate. Maybe it’s a mammalian response to over population.

hwillis 7y ago
No, that's silly. Unless mammals are magic, the only way a species could possibly know about population is by the number of individuals it sees locally, and the number they see. That would cause there to be a huge and noticeable difference between eg rural and urban populations.
- cheschire 7y ago
  Well, I didn't write an entire introduction paragraph for a research paper, sure, but outright dismissing as "silly" seems rather closed minded.

CamelCaseName 7y ago

I found this passage interesting (about the impact of climate controlled environments on resting metabolic rate) > Changes in ambient temperature may also explain some of the observed change in body temperature over time. Maintaining constant body temperature despite fluctuations in ambient temperature consumes up to 50–70% of daily energy intake (Levine, 2007). > Resting metabolic rate (RMR), for which body temperature is a crude proxy, increases when the ambient temperature decreases below or rises above the thermoneutral zone, that is the temperature of the environment at which humans can maintain normal temperature with minimum energy expenditure (Erikson et al., 1956). > ... Thus, the amount of time the population has spent at thermoneutral zones has markedly increased, potentially causing a decrease in RMR, and, by analogy, body temperature. Source: https://elifesciences.org/articles/49555 https://elifesciences.org/articles/49555

rhacker 7y ago

I wonder if they simply looked at the antibiotic use. For example when that was introduced specifically, and more so when we started "over-prescribing" it. That's got to have had an effect of persistent low grade fevers that exist in just about everyone.

hwillis 7y ago
Body temperatures are currently lower, so the opposite of what you're suggesting with low grade fevers from overprescription of antibiotics. However, fevers are caused by a subset of the interleukin family, which as a whole causes inflammation. Inflammation was the author's suggestion. Also, low grade fevers aren't a thing. Fever is caused by the immune system. You can only have a continuous infection with diseases that avoid or supress the immune system. There are a small number of brain-affecting infectious diseases like meningitis that can raise body temperature on their own. Chronically recurring stuff will also give you intermittent fevers, but there's no low-grade. You have it or you don't.

deleted 7y ago

[deleted]

mattkrause 7y ago

Link to the actual study: https://elifesciences.org/articles/49555 https://elifesciences.org/articles/49555 Protsiv, M., Ley, C., Lankester, J., Hastie, T., & Parsonnet, J. (2020). Decreasing human body temperature in the United States since the industrial revolution. eLife, 9, e49555.

hopia 7y ago

The latest temperature data was measured from patients visiting hospital. Older people are naturally more prone to health problems and would therefore be visiting hospital more than younger people, on average. Our average lifespan is longer than it used to be. I'd assume older people have a lower base temperature. This would skew the results statistically.

RhodesianHunter 7y ago
I would assume that a well constructed study would account for this.
- hopia 7y ago
  Yes, I have to admit I haven't read the actual study so this was purely speculation.
- cosmotic 7y ago
  In my experience, studies are typically not well constructed. See the numerous studies that cannot be replicated, the below-the-surface iceberg of unpublished (unfavorable) studies paid for by for-profit institutions, or the shockingly small sample set or biased sample set in most studies. Most studies expose this information implicitly but it's up to the reader to determine the bias or replicate the study.
  - hwillis 7y ago
    The study compared people born after 1990, so if there were any old people in that cohort this study would be much bigger news.
hwillis 7y ago
The study compared people born after 1990, so if there were any old people in that cohort this study would be much bigger news.

therealx 7y ago

I've noticed that my temp is always 1 degree lower than it should be. It's never been a problem and has been that way since birth.

hwillis 7y ago
The normal range of resting body temperatures is anywhere from 95 to 100 F. People vary a lot.

pandaman 7y ago

I was always confused how 37 C was a normal temperature in the US. In the USSR where I grew it was a fever and the normal was 36.6. Could it be the way it's measured?

comicjk 7y ago
Temperatures of 37 C and 36.6 C are barely distinguishable with an ordinary thermometer, and both are within the normal range of human body temperatures (37.32-38.76 C). www.ncbi.nlm.nih.gov/pmc/articles/PMC6456186
elric 7y ago
Not sure about any US/USSR differences, but there can be pretty big differences between people individually, between measurements in the same person throughout the day (or month for women), and between how it's measured. 37°C is an average. Axillary (armpit) measurements, for example, are a lot colder than oral or rectal measurements. Perhaps the Russians favoured the former, while the Americans preferred the latter? I suspect there's a nice little bell curve with 37°C in the middle.
- pandaman 7y ago
  Yes, Russia measures temperature in the armpit. Is it really that much colder than in the mouth? Edit: A 37 temperature would automatically give you an excuse from school when I was a kid and, obviously, children always were finding ways to cheat. If just putting the thermometer in your mouth worked then either I was in the dark or nobody has discovered this.
  - elric 7y ago
    Yes, the armpit is roughly 0.5°C colder than the mouth.

ZeroFries 7y ago

When I shovel the driveway, I'm sweating wearing no jacket, but I freeze sitting on the porch in a parka.

deleted 7y ago
[deleted]

bobloblaw45 7y ago

I'm leaning strongly on the side of thermometers were less accurate and gave a higher reading in the early 1800s.

hwillis 7y ago
The study was on measurements taken in the early 1900s, not 1800s. Also, it's not like technology suddenly started in the 30s or something. Liquid nitrogen was first produced in 1883. The periodic table was published in 1869. Cells were discovered in 1665. Science was a lot more than banging rocks together. You would expect the opposite of what you're suggesting, if anything. If water was used for calibrating temperature then there would be fewer good ways to control the impurity level, which would lower its freezing point. Not to mention Fahrenheit originally defined body temperature as 96 F, and it was later corrected higher. All of the above is totally moot because we have plenty of medical thermometers from the 1900s and earlier, and they are remarkably accurate and the error is not particularly biased in either way. This is a highly researched area because the accuracy of whether thermometers is important to historical and climate research. Medical thermometers from the 1800s are good to at least 1/5th of a degree and instrumentation thermometers were good to hundredths.

redwood 7y ago

Seems conceivable that higher proportion of body fat aka more insulation could also contribute

hwillis 7y ago
Fat would do the opposite. The core body temperature would be the same, because otherwise it would be too hot. The distal body temperature would be insulated from the sources of heat, so the inside of your mouth, forehead, rectum etc would be cooler.

julius_set 7y ago

I’m not sure how much this matters but I’ve been on TRT therapy for a while now and I remember before I started my limbs would get so cold, and hands would be so cold to touch. After therapy my significant other tells me I’m like a body heater constantly radiating heat possibly due to high synthesis and metabolism. I’m curious but there was a chart I saw as well regarding men’s testosterone levels declining over the last century I wonder how related that is to lowered body temperatures

mrfusion 7y ago

This could simply be a result of nationwide iodine deficiency. Our main source is fortified salt and everyone is cutting back on their sodium or using fancier salts that don’t add iodine. I make sure to put a pinch of iodized salt in everything I cook.

hwillis 7y ago
This study is from before iodine was added supplementally (1924 in the US). You are correct that iodine deficiency leads to low body temperature due to hyperthyroidism. Dairy and grain are the biggest sources of iodine. To get your iodine from salt alone would require over 3 grams per day, which is quite a lot. The average American consumes 3.4 g, DV recommendation is 2.3 g.

pattusk 7y ago

Could some of it be explained by demographic changes (immigration)? iI remember always being taught growing up than 37.5°C was the average human body temperature. However after moving to East Asia I met plenty of people who consider 37.5 a light fever and 36 the normal temp. On my phone so no data to back it up for now though...

jl2718 7y ago

A lot of comments here blame obesity/sedentary lifestyles/junk food for low body temperature. Let’s look at this: Obesity: raises temperature exercise: lowers resting temperature junk food: raises temperature What if it’s the reverse? What if your desire to eat and not exercise had a lot to do with being cold? Frankly I’m not buying the arguments in the article. Occam’s razor says it’s a common nutritional deficiency or environmental toxin affecting the thyroid.

jl2718 7y ago
Anecdote: I’ve been getting noticeably colder every year for no natural reason, so I’ve tried many things: fish oil, iodine etc. The only thing that worked was iron. I took 600mg ferrous gluconate with 5g vitamin C, and I was sweating hot and felt amazing for the next 24 hours. Iron overdose can be deadly and irreversible, so I have not repeated this and do not recommend it.