7 ms·

The Mysterious Aging of Astronauts

152 points by avani 11y ago

dennisnedry 11y ago
Perhaps there needs to be more studies done on the effect of gravity and human health? Conversely, are there other things in our air (pollutants) that are in fact causing slower aging when on Earth?
- caio1982 11y ago
  Well, as to your first question, that's exactly the purpose of https://www.nasa.gov/content/one-year-crew https://www.nasa.gov/content/one-year-crew
eveningcoffee 11y ago
I like the comment from petero: Perhaps the effect is due to lack of grounding.
username3 11y ago
Certain bacteria in bodies die in space?
- dogma1138 11y ago
  If they absorbed sufficient radiation to kill that much bacteria they would be dead a week later. If you get a dose high enough to give you "radiation high" you are a goner.
kayadx83 11y ago
This is interesting. You feel gravity less when you are in fluids. Does this mean all babies feel gravity differently because we all experience different amounts of fluid in the womb (not to mention the variations in baby sizes)? The impact is probably miniscule but I wonder if it has any effect on development of babies in the womb.
- amelius 11y ago
  I guess you feel it less only because the support (pressure) is distributed more evenly along your skin. Inside your body, almost everything is fluid, so there it does not matter much, I'd say.
- hydrogen18 11y ago
  How exactly do you think buoyancy works? It's not like its anti-gravity anymore than the chair I'm sitting in is.
dogma1138 11y ago
So the dawn of the 20th century radium spas are going to make a come back? https://en.wikipedia.org/wiki/History_of_radiation_therapy#Joachimsthal_radium_spa_hotel https://en.wikipedia.org/wiki/History_of_radiation_therapy#J...
deleted 11y ago
[deleted]
- notacoward 11y ago
  That's a nice theory, but I'm going to call [citation needed] anyway. Can you cite any explanations of how weightlessness would cause something like cataracts or insulin resistance, or even of whether there's a statistically significant correlation focusing on the single variable of weightlessness vs. others that might be involved?
  - taconacho 11y ago
    The symptoms match health effects caused by a sedentary lifestyle: https://en.wikipedia.org/wiki/Sedentary_lifestyle#Health_effects https://en.wikipedia.org/wiki/Sedentary_lifestyle#Health_eff... . In a gravitational environment, just moving around is a form of exercise since one has to move about the entire weight of one's body. In space, where everything is weightless, it takes much less effort to move around and you see the same effects (even with rigorous exercise routines). Imagine exercising for an hour or two and then sitting down for the other 22 hours. You'd end up with similar health effects.
    - notacoward 11y ago
      Your own source contradicts that last claim. "those that exercise at least 4 hours per week are as healthy as those that sit fewer than 4 hours" Readable copy of the paper on which that article is based: http://www.researchgate.net/publication/46255258_Occupational_Sitting_and_Health_Risks http://www.researchgate.net/publication/46255258_Occupationa... The authors found a "convincing" correlation between sedentary behavior and health risks only for for cancer and CVD (see the "discussion" section). They specifically looked for such a correlation to insulin resistance, but didn't find any; they didn't look for other symptoms that have been mentioned (e.g. cataracts) at all. It's not at all clear that weightlessness is the same as sitting at a desk in terms of the conditions we're talking about, but there is evidence that their rigorous exercise programs should counteract any such effects anyway. I'm not saying your theory is invalid, but you've done anything but provide evidence for it. It's certainly not the kind of "slam dunk" that would have justified your haughty dismissal of the OP.
taconacho 11y ago
Is there a citation for the following claim? I've never heard of such a thing: "But then more results started coming back. Not only do astronauts come back with weak muscles and frail bones… But they also suffer from skin thinning, atherosclerosis (stiffer arteries), resistance to insulin and they suffer from loss of vision due to cataracts many years earlier than expected given their chronological age. These symptoms look a lot like skin aging, cardiovascular aging, age-related diabetes and so forth. In fact, it is pretty accurate to say that astronauts age at an accelerated rate."
- kbenson 11y ago
  There's a slew of references ("further reading") listed at the bottom, some of them look like they are the source of at least some of these claims.
- danesparza 11y ago
  In addition to the references in the article, Wikipedia (surprisingly) has a nice article on the effects of spaceflight on the human body (with all sorts of references): https://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_human_body https://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_h...
  - taconacho 11y ago
    Looks like my mistake was in thinking that the stated effects were occurring after astronauts had returned to Earth. At least that's what the title sounds like. If these symptoms only apply to humans while they are in a weightless environment then it sounds very much like sedentary disease (aka sitting disease). Even rigorous exercise routines can't fully match the effects of gravity on the human body.
- toomuchtodo 11y ago
  They're not aging at an accelerated rate, they're exhibiting similar symptoms of aging from their microgravity environment (weak muscles, frail bones) and from there being no shielding from cosmic rays (cataracts).
mmastrac 11y ago
Cache since it appears to be dead: http://webcache.googleusercontent.com/search?q=cache:SYsBpU-28V4J:lemire.me/blog/2015/12/01/the-mysterious-aging-of-astronauts/&hl=en&gl=us&strip=1&vwsrc=0 http://webcache.googleusercontent.com/search?q=cache:SYsBpU-...
jimrandomh 11y ago
Maybe there's a diet-related problem? Astronaut food has some pretty intense constraints that Earth food doesn't, and has almost certainly been optimized according to the false discoveries of the field of nutrition. They should have a few people with different contrarian positions look over the food logs, and see if there's anything really wrong there.
- pc86 11y ago
  > false discoveries of the field of nutrition I would love to hear about some of these.
  - Evgeny 11y ago
    My guess is that he meant things like "fat makes you fat and causes heart disease", or "fruit juice is good for you", or "margarine is better for you than butter" or "meat causes cancer" etc.
    - jimrandomh 11y ago
      Yes, these are all examples or tentative examples of the sort of thing I'm talking about. (I don't know much about what they're eating up on the ISS, though, so I don't know if they're applicable.)
S_A_P 11y ago
Sounds to me that its related to the "exercise" related to living in 1G. I wonder if the air mixture oxidizes the body more quickly as well.
LordKano 11y ago
Maybe it's attributed to the rigorousness of the selection process but I have noticed the longevity of so many astronauts. John Glenn, Neil Armstrong, Buzz Aldrin, Michael Collins and Edgar Mitchell all lived beyond the average life expectancy of American males born when they were born. Our bodies have incredibly complex feedback loops and we evolved here, with a constant 1G of gravity. It's not surprising to me that exposure to Zero-G can have long lasting and unexpected consequences.
- Retric 11y ago
  Selection bias. Life expectancy at birth has little impact when astronauts are all selected much latter in life. At the extreme edge, the average age of people in nursing homes is much older than life expectancy at birth. That does not mean nursing homes are good for you.
  - LordKano 11y ago
    I certainly concede the possibility. People who are healthiest in their mid to late 30s being more likely to live into old age than those who are not is a plausible explanation for what I have observed.
    - Retric 11y ago
      I think we are talking past each other. People who are alive at 30 can't die at 5, but people at birth could die at 5. So, just by being 30+ or 60+ a populations life expectancy increases. Which is why actuarial tables include ages. So, to see if Astronauts are living unusually longer than other people you need to look at life expectancy's of people who where 30 around 1960's. Now, they might sill be living longer than that group. But, it does not seem like that's the comparison your making.
      - nilkn 11y ago
        https://www.ssa.gov/oact/STATS/table4c6.html https://www.ssa.gov/oact/STATS/table4c6.html This suggests a life expectancy of ~78 years old for someone 30 years old today. Of course, as you stated, we'd really need statistics for someone who was 30 years old in the 60s. John Glenn, Neil Armstrong, Buzz Aldrin, Michael Collins and Edgar Mitchell are all at least several years beyond 78, with Glenn at an impressive 94. By the way, the life expectancy at birth in that table is 76, so evidently reaching age 30 doesn't actually count for as much as I thought it would.
deleted 11y ago
[deleted]
deleted 11y ago
[deleted]
- DaveMebs 11y ago
  Please read the article before posting. The author specifically discusses the fact that astronauts show signs of aging more rapidly despite the fact that small doses of radiation can be good for your health.
- tantalor 11y ago
  Huh? They aren't long lived... that's the concern!
zeristor 11y ago
I attended a talk [1] in which the made a case for the a British manned space programme as another angle on investigating ageing [2]. Radiation, boneloss, and a number of aspects. Ironically my memory of the talk is fading... [1] http://www.bis-space.com/2014/03/04/12501/uk-space-life-and-biomedical-sciences-a-launchpad-for-british-human-space-flight http://www.bis-space.com/2014/03/04/12501/uk-space-life-and-... [2] http://www.ukspacelabs.co.uk/about/5-strategy-r-d-themes http://www.ukspacelabs.co.uk/about/5-strategy-r-d-themes
pcl 11y ago
They are also followed medically more closely than just about anyone on Earth: they don’t indulge in regular fast food I wonder what they mean by that. Are astronauts explicitly banned from eating fast food, and somehow monitored? Or are they just less likely to eat fast food, since they pay close attention to their fitness and health?
- derekp7 11y ago
  As far as I know, they haven't installed a McDonald's module on the ISS yet.
stephengoodwin 11y ago
On the reverse side, I've always wondered if being in a weightless environment makes your muscles feel great[0], since they aren't working against gravity. Over the years, gravity can create lots of problems for posture, which is why swimming (which lessen the effects of gravity) feels great. [0] I'm using "Feel" in a relative context, since muscle weakness/wasting will not feel good once you're back in a non-weightless environment.
- kbutler 11y ago
  My experience with swimming is that the drag from the resistant medium outweighs the perceived "lift" from buoyancy. I expect the disorientation, nausea, etc., would outweigh any short term muscle-feel effects. For how weightlessness feels: http://science.howstuffworks.com/weightlessness2.htm http://science.howstuffworks.com/weightlessness2.htm
jostmey 11y ago
One hypothesis: Solar and cosmic ionizing radiation ?
Joof 11y ago
Microgravity is like alcohol; it effects so many systems in your body that it's really difficult to pin down exactly what is causing problems where. I imagine this question won't be seriously answered until we have an artificial gravity system.
bizarref00l 11y ago
It seems strange aging also affects other things. http://www.japantimes.co.jp/news/2014/04/11/national/sakura-from-space-blooms-early/ http://www.japantimes.co.jp/news/2014/04/11/national/sakura-...
thieving_magpie 11y ago
I love this sentence, cracks me up: "They are also followed medically more closely than just about anyone on Earth: they don’t indulge in regular fast food."
tullianus 11y ago
I'll repost the comment I made over there: Have you guys heard about the entire field of study that is aerospace medicine? I’m taking a course on it this semester (I’m a masters student in aerospace engineering)–let me summarize some of the problems that your body goes through during space travel. Humans spend about 70% of their time either standing or sitting. That means the human body is optimized for a hydrostatic pressure gradient like the one illustrated here (http://wiki.sdstate.edu/@api/deki/files/999/=1-BP_Change.png http://wiki.sdstate.edu/@api/deki/files/999/=1-BP_Change.png). Blood pressure is much higher at your feet than at your head. In space, however, there is no gravity to produce this gradient, so the cardiovascular system equalizes its pressure. That’s why astronauts suffer from “puffy face” (higher-than-usual fluid pressures in head) and “chicken legs” (lower-than-usual fluid pressures in legs). In their first couple days in space, astronauts lose about 1L of leg volume from each leg. The CV system relies on internal pressure sensors to figure out how to operate, and the new pressure distribution confuses it. Astronauts lose a lot of blood plasma–it sort of ends up absorbed into the surrounding tissues. This increases the relative concentration of red blood cells, which triggers the body to slow down production of new ones. Also, the heart atrophies because it doesn’t need to pump as hard to move liquid around the body. When you come back from space, your body needs to rapidly readapt from microgravity to one gee. It is not very good at doing that. That’s why 63% of astronauts are unable to stand for ten minutes straight just after their return from short-duration space missions (see video: https://www.youtube.com/watch?v=TPDST7EePXQ https://www.youtube.com/watch?v=TPDST7EePXQ). There are other problems: the cells that are constantly building and destroying your bones fall out of alignment when you’re in microgravity, causing astronauts’ bones to change structure in a way that looks a lot like accelerated aging. Why? Not clear, but possibly related to the lack of repeated loading, as happens when you stand/walk in normal gravity. Astronauts end up with huge concentrations of calcium in their blood, which causes kidney stones. Astronauts in space average around 4 hours of sleep per night, and very few of them eat enough calories to maintain their body weight, so they lose muscle mass. Aerospace medicine is about half medical studies of astronauts and half studies of people on earth. It turns out that you can make most of these body changes happen by having people lie on their backs with the bed tilted down six degrees (head downward). Fascinating field. If you want to know more, I recommend the textbook “Space Physiology” by Jay Buckey (amazon link here: http://smile.amazon.com/Space-Physiology-Jay-C-Buckey/dp/0195137256?tag=s4charity-20 http://smile.amazon.com/Space-Physiology-Jay-C-Buckey/dp/019...).

152 points by avani 11y ago

Perhaps there needs to be more studies done on the effect of gravity and human health? Conversely, are there other things in our air (pollutants) that are in fact causing slower aging when on Earth?

caio1982 11y ago
Well, as to your first question, that's exactly the purpose of https://www.nasa.gov/content/one-year-crew https://www.nasa.gov/content/one-year-crew

eveningcoffee 11y ago

I like the comment from petero: Perhaps the effect is due to lack of grounding.

username3 11y ago

Certain bacteria in bodies die in space?

dogma1138 11y ago
If they absorbed sufficient radiation to kill that much bacteria they would be dead a week later. If you get a dose high enough to give you "radiation high" you are a goner.

kayadx83 11y ago

This is interesting. You feel gravity less when you are in fluids. Does this mean all babies feel gravity differently because we all experience different amounts of fluid in the womb (not to mention the variations in baby sizes)? The impact is probably miniscule but I wonder if it has any effect on development of babies in the womb.

amelius 11y ago
I guess you feel it less only because the support (pressure) is distributed more evenly along your skin. Inside your body, almost everything is fluid, so there it does not matter much, I'd say.
hydrogen18 11y ago
How exactly do you think buoyancy works? It's not like its anti-gravity anymore than the chair I'm sitting in is.

dogma1138 11y ago

So the dawn of the 20th century radium spas are going to make a come back? https://en.wikipedia.org/wiki/History_of_radiation_therapy#Joachimsthal_radium_spa_hotel https://en.wikipedia.org/wiki/History_of_radiation_therapy#J...

deleted 11y ago

[deleted]

notacoward 11y ago
That's a nice theory, but I'm going to call [citation needed] anyway. Can you cite any explanations of how weightlessness would cause something like cataracts or insulin resistance, or even of whether there's a statistically significant correlation focusing on the single variable of weightlessness vs. others that might be involved?
- taconacho 11y ago
  The symptoms match health effects caused by a sedentary lifestyle: https://en.wikipedia.org/wiki/Sedentary_lifestyle#Health_effects https://en.wikipedia.org/wiki/Sedentary_lifestyle#Health_eff... . In a gravitational environment, just moving around is a form of exercise since one has to move about the entire weight of one's body. In space, where everything is weightless, it takes much less effort to move around and you see the same effects (even with rigorous exercise routines). Imagine exercising for an hour or two and then sitting down for the other 22 hours. You'd end up with similar health effects.
  - notacoward 11y ago
    Your own source contradicts that last claim. "those that exercise at least 4 hours per week are as healthy as those that sit fewer than 4 hours" Readable copy of the paper on which that article is based: http://www.researchgate.net/publication/46255258_Occupational_Sitting_and_Health_Risks http://www.researchgate.net/publication/46255258_Occupationa... The authors found a "convincing" correlation between sedentary behavior and health risks only for for cancer and CVD (see the "discussion" section). They specifically looked for such a correlation to insulin resistance, but didn't find any; they didn't look for other symptoms that have been mentioned (e.g. cataracts) at all. It's not at all clear that weightlessness is the same as sitting at a desk in terms of the conditions we're talking about, but there is evidence that their rigorous exercise programs should counteract any such effects anyway. I'm not saying your theory is invalid, but you've done anything but provide evidence for it. It's certainly not the kind of "slam dunk" that would have justified your haughty dismissal of the OP.

taconacho 11y ago

Is there a citation for the following claim? I've never heard of such a thing: "But then more results started coming back. Not only do astronauts come back with weak muscles and frail bones… But they also suffer from skin thinning, atherosclerosis (stiffer arteries), resistance to insulin and they suffer from loss of vision due to cataracts many years earlier than expected given their chronological age. These symptoms look a lot like skin aging, cardiovascular aging, age-related diabetes and so forth. In fact, it is pretty accurate to say that astronauts age at an accelerated rate."

kbenson 11y ago
There's a slew of references ("further reading") listed at the bottom, some of them look like they are the source of at least some of these claims.
danesparza 11y ago
In addition to the references in the article, Wikipedia (surprisingly) has a nice article on the effects of spaceflight on the human body (with all sorts of references): https://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_human_body https://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_h...
- taconacho 11y ago
  Looks like my mistake was in thinking that the stated effects were occurring after astronauts had returned to Earth. At least that's what the title sounds like. If these symptoms only apply to humans while they are in a weightless environment then it sounds very much like sedentary disease (aka sitting disease). Even rigorous exercise routines can't fully match the effects of gravity on the human body.
toomuchtodo 11y ago
They're not aging at an accelerated rate, they're exhibiting similar symptoms of aging from their microgravity environment (weak muscles, frail bones) and from there being no shielding from cosmic rays (cataracts).

mmastrac 11y ago

Cache since it appears to be dead: http://webcache.googleusercontent.com/search?q=cache:SYsBpU-28V4J:lemire.me/blog/2015/12/01/the-mysterious-aging-of-astronauts/&hl=en&gl=us&strip=1&vwsrc=0 http://webcache.googleusercontent.com/search?q=cache:SYsBpU-...

jimrandomh 11y ago

Maybe there's a diet-related problem? Astronaut food has some pretty intense constraints that Earth food doesn't, and has almost certainly been optimized according to the false discoveries of the field of nutrition. They should have a few people with different contrarian positions look over the food logs, and see if there's anything really wrong there.

pc86 11y ago
> false discoveries of the field of nutrition I would love to hear about some of these.
- Evgeny 11y ago
  My guess is that he meant things like "fat makes you fat and causes heart disease", or "fruit juice is good for you", or "margarine is better for you than butter" or "meat causes cancer" etc.
  - jimrandomh 11y ago
    Yes, these are all examples or tentative examples of the sort of thing I'm talking about. (I don't know much about what they're eating up on the ISS, though, so I don't know if they're applicable.)

S_A_P 11y ago

Sounds to me that its related to the "exercise" related to living in 1G. I wonder if the air mixture oxidizes the body more quickly as well.

LordKano 11y ago

Maybe it's attributed to the rigorousness of the selection process but I have noticed the longevity of so many astronauts. John Glenn, Neil Armstrong, Buzz Aldrin, Michael Collins and Edgar Mitchell all lived beyond the average life expectancy of American males born when they were born. Our bodies have incredibly complex feedback loops and we evolved here, with a constant 1G of gravity. It's not surprising to me that exposure to Zero-G can have long lasting and unexpected consequences.

Retric 11y ago
Selection bias. Life expectancy at birth has little impact when astronauts are all selected much latter in life. At the extreme edge, the average age of people in nursing homes is much older than life expectancy at birth. That does not mean nursing homes are good for you.
- LordKano 11y ago
  I certainly concede the possibility. People who are healthiest in their mid to late 30s being more likely to live into old age than those who are not is a plausible explanation for what I have observed.
  - Retric 11y ago
    I think we are talking past each other. People who are alive at 30 can't die at 5, but people at birth could die at 5. So, just by being 30+ or 60+ a populations life expectancy increases. Which is why actuarial tables include ages. So, to see if Astronauts are living unusually longer than other people you need to look at life expectancy's of people who where 30 around 1960's. Now, they might sill be living longer than that group. But, it does not seem like that's the comparison your making.
    - nilkn 11y ago
      https://www.ssa.gov/oact/STATS/table4c6.html https://www.ssa.gov/oact/STATS/table4c6.html This suggests a life expectancy of ~78 years old for someone 30 years old today. Of course, as you stated, we'd really need statistics for someone who was 30 years old in the 60s. John Glenn, Neil Armstrong, Buzz Aldrin, Michael Collins and Edgar Mitchell are all at least several years beyond 78, with Glenn at an impressive 94. By the way, the life expectancy at birth in that table is 76, so evidently reaching age 30 doesn't actually count for as much as I thought it would.

deleted 11y ago

[deleted]

deleted 11y ago

[deleted]

DaveMebs 11y ago
Please read the article before posting. The author specifically discusses the fact that astronauts show signs of aging more rapidly despite the fact that small doses of radiation can be good for your health.
tantalor 11y ago
Huh? They aren't long lived... that's the concern!

zeristor 11y ago

I attended a talk [1] in which the made a case for the a British manned space programme as another angle on investigating ageing [2]. Radiation, boneloss, and a number of aspects. Ironically my memory of the talk is fading... [1] http://www.bis-space.com/2014/03/04/12501/uk-space-life-and-biomedical-sciences-a-launchpad-for-british-human-space-flight http://www.bis-space.com/2014/03/04/12501/uk-space-life-and-... [2] http://www.ukspacelabs.co.uk/about/5-strategy-r-d-themes http://www.ukspacelabs.co.uk/about/5-strategy-r-d-themes

pcl 11y ago

They are also followed medically more closely than just about anyone on Earth: they don’t indulge in regular fast food I wonder what they mean by that. Are astronauts explicitly banned from eating fast food, and somehow monitored? Or are they just less likely to eat fast food, since they pay close attention to their fitness and health?

derekp7 11y ago
As far as I know, they haven't installed a McDonald's module on the ISS yet.

stephengoodwin 11y ago

On the reverse side, I've always wondered if being in a weightless environment makes your muscles feel great[0], since they aren't working against gravity. Over the years, gravity can create lots of problems for posture, which is why swimming (which lessen the effects of gravity) feels great. [0] I'm using "Feel" in a relative context, since muscle weakness/wasting will not feel good once you're back in a non-weightless environment.

kbutler 11y ago
My experience with swimming is that the drag from the resistant medium outweighs the perceived "lift" from buoyancy. I expect the disorientation, nausea, etc., would outweigh any short term muscle-feel effects. For how weightlessness feels: http://science.howstuffworks.com/weightlessness2.htm http://science.howstuffworks.com/weightlessness2.htm

jostmey 11y ago

One hypothesis: Solar and cosmic ionizing radiation ?

Joof 11y ago

Microgravity is like alcohol; it effects so many systems in your body that it's really difficult to pin down exactly what is causing problems where. I imagine this question won't be seriously answered until we have an artificial gravity system.

bizarref00l 11y ago

It seems strange aging also affects other things. http://www.japantimes.co.jp/news/2014/04/11/national/sakura-from-space-blooms-early/ http://www.japantimes.co.jp/news/2014/04/11/national/sakura-...

thieving_magpie 11y ago

I love this sentence, cracks me up: "They are also followed medically more closely than just about anyone on Earth: they don’t indulge in regular fast food."

tullianus 11y ago

I'll repost the comment I made over there: Have you guys heard about the entire field of study that is aerospace medicine? I’m taking a course on it this semester (I’m a masters student in aerospace engineering)–let me summarize some of the problems that your body goes through during space travel. Humans spend about 70% of their time either standing or sitting. That means the human body is optimized for a hydrostatic pressure gradient like the one illustrated here (http://wiki.sdstate.edu/@api/deki/files/999/=1-BP_Change.png http://wiki.sdstate.edu/@api/deki/files/999/=1-BP_Change.png). Blood pressure is much higher at your feet than at your head. In space, however, there is no gravity to produce this gradient, so the cardiovascular system equalizes its pressure. That’s why astronauts suffer from “puffy face” (higher-than-usual fluid pressures in head) and “chicken legs” (lower-than-usual fluid pressures in legs). In their first couple days in space, astronauts lose about 1L of leg volume from each leg. The CV system relies on internal pressure sensors to figure out how to operate, and the new pressure distribution confuses it. Astronauts lose a lot of blood plasma–it sort of ends up absorbed into the surrounding tissues. This increases the relative concentration of red blood cells, which triggers the body to slow down production of new ones. Also, the heart atrophies because it doesn’t need to pump as hard to move liquid around the body. When you come back from space, your body needs to rapidly readapt from microgravity to one gee. It is not very good at doing that. That’s why 63% of astronauts are unable to stand for ten minutes straight just after their return from short-duration space missions (see video: https://www.youtube.com/watch?v=TPDST7EePXQ https://www.youtube.com/watch?v=TPDST7EePXQ). There are other problems: the cells that are constantly building and destroying your bones fall out of alignment when you’re in microgravity, causing astronauts’ bones to change structure in a way that looks a lot like accelerated aging. Why? Not clear, but possibly related to the lack of repeated loading, as happens when you stand/walk in normal gravity. Astronauts end up with huge concentrations of calcium in their blood, which causes kidney stones. Astronauts in space average around 4 hours of sleep per night, and very few of them eat enough calories to maintain their body weight, so they lose muscle mass. Aerospace medicine is about half medical studies of astronauts and half studies of people on earth. It turns out that you can make most of these body changes happen by having people lie on their backs with the bed tilted down six degrees (head downward). Fascinating field. If you want to know more, I recommend the textbook “Space Physiology” by Jay Buckey (amazon link here: http://smile.amazon.com/Space-Physiology-Jay-C-Buckey/dp/0195137256?tag=s4charity-20 http://smile.amazon.com/Space-Physiology-Jay-C-Buckey/dp/019...).