7 ms·

Infection inflicts a persistent decrease in IQ: study with 180,000 participants

83 points by mocha-rain 11y ago

demylinateme 11y ago
Why do viral infections have a stronger effect on IQ than bacterial?
- fleitz 11y ago
  My guess would be viruses more easily pass the blood/brain barrier?
  - eru 11y ago
    Viruses are also fought differently by the immune system.
- IndianAstronaut 11y ago
  Parasites seem to also have a significant impact on IQ and poverty as well. http://www.economist.com/node/16479286/print http://www.economist.com/node/16479286/print
- IndianAstronaut 11y ago
  Parasites seem to also have a significant impact on IQ and poverty as well. http://www.economist.com/node/16479286/print http://www.economist.com/node/16479286/print
farresito 11y ago
This sort of news really scare me. Your brain defines who you are and what capabilities you have, and damaging it can completely change you. The brain is very responsible for a big part of your success and losing it can have a big impact in your life.
- madaxe_again 11y ago
  Cognitive decline happens whether you like it or not, I'm afraid to say. I've hit my early 30s and I've started noticing that I'm far more prone to inappropriately replaced words, can't memorise long strings of digits as well as I used to be able to, and so-forth.
  - unclebucknasty 11y ago
    >I've hit my early 30s and I've started noticing that I'm far more prone... That's a really young age to have any sort of marked age-related cognitive decline. It might be explained by something else--even something as "simple" as insufficient quality sleep or stress, both of which can wreak havoc on cognitive ability.
  - melted 11y ago
    This could be because you're not getting enough sleep (or aren't sleeping well due to e.g. apnea or something). Set up a simple experiment: go to bed 1-1.5 hours earlier than you usually do for a couple of weeks and see if your "cognitive decline" disappears. As you age you might find you need more sleep.
    - jacquesm 11y ago
      > As you age you might find you need more sleep. This is very true for me, much to my surprise. I used to get by on 3 to 4 hours every night but that seems to have really caught up with me. If I don't get 8 hours minimum now I'm woozy the rest of the day.
      - unclebucknasty 11y ago
        Same here. And "buzzy" when I'm really sleep-deprived. It literally feels like low-level electrical interference running through my head and my thinking and focus are nowhere near as sharp. It is like some sort of intoxication, which is fitting, because one of the things sleep does for us is clear toxins from our brains.
madaxe_again 11y ago
Interesting study, but as the authors concede, one can't quite rule out that the causal flow is in the opposite direction to that which they propose - that is, people with lower cognitive ability are more likely to end up with infections, and people with much lower cognitive ability are more likely to end up with severe infections. I mean, consider people with dementia, sat in their own faeces (at the severely diminished/severe infection end of the scale), or people with lower intellect lower on the socio-economic scale engaging with jobs where they're more likely to end up with infections - construction, handling hazardous waste, etc. etc.
- unclebucknasty 11y ago
  >this reverse association could not account for the observed temporal correlations or the correlations with the severity of infection. Moreover, the correlation between infections and cognitive ability retained significance even after adjustment for other parameters known to influence general cognitive ability...which are also associated with socio-economic gradients. Could possibly be both.
- mocha-rain 11y ago
  I'm sympathetic to your point of view; in some cases it seems nearly impossible to rigorously exclude reverse-associations when there are so many complexities. The authors respond to this objection as follows: The finding that infections are associated with decreased general cognitive ability after a latency period might be an epiphenomenon and not a biologically-mediated relationship. For instance, a reverse association could have existed so that lower cognitive ability may be a risk factor for acquiring infections. Furthermore, studies have indicated that immune related genes might be implicated in cognition [34], and individuals with genetic liability towards a lower general cognitive ability might also be more genetically vulnerable towards infections. However, although a genetic or reverse association could have partly explained some of the observed associations, this probably does not account for the observed temporal associations or the associations with severity of the infection. The association between infections and cognitive ability remained significant after adjusting for other factors known to influence a decrease of general cognitive ability, such as gestational age, birth weight [35], and having more older siblings (i.e. being later in a sibship), which often correlate with socio-economic gradients [36]. ..Nevertheless, the findings remained significant also after adjustment for an individual or family history of psychiatric disorders and substance abuse which could be associated with several of these unmeasured risk factors as well as socio-economic factors. Furthermore, the possible effect of maternal smoking during pregnancy should to some degree be captured by the included birth weight and gestational age in the adjustments. Moreover, there may be diseases that are associated with both increased susceptibility to infections and somewhat lower cognition (either the disease itself or its treatment).
BoardsOfCanada 11y ago
The p-value (a function used for testing a statistical hypothesis) corresponding to these results was less than 0.001, indicating that the probability that the findings were due to chance alone (or that the null hypothesis is true) is less than 0.1%. Actually, I think it means that IF the null hypothesis is true, there is only a 0.1% chance that we would get this much deviation (or more) from it due to chance. Which isn't the same thing. Still, seems like a significant result of course, but let's be correct about these things.
- axonopathy 11y ago
  It looks like the author took this comment to heart.
- eru 11y ago
  axonopathy, it seems you are hell-banned for some reason..
- solve 11y ago
  The whole science industry should follow the lead of those scientific journals who've banned p-values from their publications. P-values just lead to so much confusion and nonsense. And that's without even considering the scientists who cheat the p-values, which is actually just a tiny part of the problem with p-values.
  - _-__--- 11y ago
    I think that the outright banning of p-values is not the right way to go. The researchers that misuse them and the reviewers that apparently don't understand them are a much bigger problem than the p-value metric itself. What's needed is a better understanding of empirical conditional statistics and the application of that understanding to the degign of experiments and the analysis of the results produced therefrom.
    - solve 11y ago
      And the best way to do that is to eliminate the crutch. Many of the more data-centric fields did away with p-values long ago in favor of far more robust approaches to establishing the value of a paper. Look at papers in the data science field. Using p-values in a paper there would get you laughed out of the industry fast. Only problem that p-values ever solved was allowing journal reviewers to be lazier, helping scientists to be lazier, and making writing more sensational press releases easier.
stefantalpalaru 11y ago
Here's the scientific article: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124005 http://journals.plos.org/plosone/article?id=10.1371/journal....
ExpiredLink 11y ago
It's merely correlation, not causation. P.S.: Why do most articles about the 'brain' try to dumb down people?
danieltillett 11y ago
Interesting study. Intelligence and the immune system share a common property in that they are have a very large number of genes influencing them (several thousand). I would not be surprised if there is quite a bit of overlap in the genes that contibute to both intelligence and immunity. What we might be seeing here is the effect of null mutations in genes that effect both immunity and intellegence.
artnep 11y ago
I've only read the abstract, but it looks like the actual effect isn't huge. People with 10 hospitalizations scored lower by .37 SD = 6 iq points.
- felixbraun 11y ago
  > Cognitive ability score (Børge Prien’s Prøve Test) has here been converted to parallel conventional IQ scaling, with a mean of 100 and an SD of 15, to give a more familiar metric of effect size. I have no idea what 6 points mean in this setting.
  - abandonliberty 11y ago
    I would assume a normal distribution where 68% of the population land between 85 and 115. Or a movement of .4 SD. [0] Nearly 16% of people would lie between 97 and 103. [1] It's 40% of a full letter grade[2] [0]http://en.wikipedia.org/wiki/Standard_deviation http://en.wikipedia.org/wiki/Standard_deviation [1]http://www.wolframalpha.com/input/?i=area+e%5E%28-1%2F450+%28-100%2Bx%29%5E2%29%2F%2815+sqrt%282+%CF%80%29%29%2C+x%3D97+to+103 http://www.wolframalpha.com/input/?i=area+e%5E%28-1%2F450+%2... [2]http://en.wikipedia.org/wiki/Academic_grading_in_the_United_States#Rank-based_grading http://en.wikipedia.org/wiki/Academic_grading_in_the_United_...
Madmallard 11y ago
It's probably not the infection itself, but the fluoroquinolones or other bacteriocidal antibiotics that they give people, that are causing mitochondrial dysfunction in the brain. -_-
- gus_massa 11y ago
  Never thought bout this, but it's clear that it's possible to have an "antibiotic" that target the mitochondria but leave the rest of the cell alive (for a while). That will be a poison, and be not useful as a actual antibiotic. I there a well know substance like this?
leeleelee 11y ago
This is a premature conclusion. There was no measurement of IQ before and after infection, so no such conclusion can be made. There could be other, unknown, factors that happen to affect BOTH: a person's IQ and their likelihood to be infected, along with severity of infection. For example some genetic, environmental, or other variable that affects your IQ as well as infection-resistance. It very well might be true, that infection does have the ability to lower IQ. But this study does not prove it. I wish scientists would be more straightforward about conclusions. The title of the article should read: "Study finds that individuals who have suffered infection have a lower IQ than the general population" or something along those lines. Much different than saying that "infection lowers IQ". This is beginner-level confusion of causation and correlation.
- pdabbadabba 11y ago
  The title of the article is, in fact "The Association between Infections and General Cognitive Ability in Young Men - A Nationwide Study." And as others have pointed out elsewhere, the authors controlled for some (though not every) conceivable common causes of infection and reduced IQ. Though, as a criticism of the author of the blog post, I would agree with your comment.
  - leeleelee 11y ago
    Ah, you are correct. I missed that.

83 points by mocha-rain 11y ago

demylinateme 11y ago

Why do viral infections have a stronger effect on IQ than bacterial?

fleitz 11y ago
My guess would be viruses more easily pass the blood/brain barrier?
- eru 11y ago
  Viruses are also fought differently by the immune system.
IndianAstronaut 11y ago
Parasites seem to also have a significant impact on IQ and poverty as well. http://www.economist.com/node/16479286/print http://www.economist.com/node/16479286/print
IndianAstronaut 11y ago
Parasites seem to also have a significant impact on IQ and poverty as well. http://www.economist.com/node/16479286/print http://www.economist.com/node/16479286/print

farresito 11y ago

This sort of news really scare me. Your brain defines who you are and what capabilities you have, and damaging it can completely change you. The brain is very responsible for a big part of your success and losing it can have a big impact in your life.

madaxe_again 11y ago
Cognitive decline happens whether you like it or not, I'm afraid to say. I've hit my early 30s and I've started noticing that I'm far more prone to inappropriately replaced words, can't memorise long strings of digits as well as I used to be able to, and so-forth.
- unclebucknasty 11y ago
  >I've hit my early 30s and I've started noticing that I'm far more prone... That's a really young age to have any sort of marked age-related cognitive decline. It might be explained by something else--even something as "simple" as insufficient quality sleep or stress, both of which can wreak havoc on cognitive ability.
- melted 11y ago
  This could be because you're not getting enough sleep (or aren't sleeping well due to e.g. apnea or something). Set up a simple experiment: go to bed 1-1.5 hours earlier than you usually do for a couple of weeks and see if your "cognitive decline" disappears. As you age you might find you need more sleep.
  - jacquesm 11y ago
    > As you age you might find you need more sleep. This is very true for me, much to my surprise. I used to get by on 3 to 4 hours every night but that seems to have really caught up with me. If I don't get 8 hours minimum now I'm woozy the rest of the day.
    - unclebucknasty 11y ago
      Same here. And "buzzy" when I'm really sleep-deprived. It literally feels like low-level electrical interference running through my head and my thinking and focus are nowhere near as sharp. It is like some sort of intoxication, which is fitting, because one of the things sleep does for us is clear toxins from our brains.

madaxe_again 11y ago

Interesting study, but as the authors concede, one can't quite rule out that the causal flow is in the opposite direction to that which they propose - that is, people with lower cognitive ability are more likely to end up with infections, and people with much lower cognitive ability are more likely to end up with severe infections. I mean, consider people with dementia, sat in their own faeces (at the severely diminished/severe infection end of the scale), or people with lower intellect lower on the socio-economic scale engaging with jobs where they're more likely to end up with infections - construction, handling hazardous waste, etc. etc.

unclebucknasty 11y ago
>this reverse association could not account for the observed temporal correlations or the correlations with the severity of infection. Moreover, the correlation between infections and cognitive ability retained significance even after adjustment for other parameters known to influence general cognitive ability...which are also associated with socio-economic gradients. Could possibly be both.
mocha-rain 11y ago
I'm sympathetic to your point of view; in some cases it seems nearly impossible to rigorously exclude reverse-associations when there are so many complexities. The authors respond to this objection as follows: The finding that infections are associated with decreased general cognitive ability after a latency period might be an epiphenomenon and not a biologically-mediated relationship. For instance, a reverse association could have existed so that lower cognitive ability may be a risk factor for acquiring infections. Furthermore, studies have indicated that immune related genes might be implicated in cognition [34], and individuals with genetic liability towards a lower general cognitive ability might also be more genetically vulnerable towards infections. However, although a genetic or reverse association could have partly explained some of the observed associations, this probably does not account for the observed temporal associations or the associations with severity of the infection. The association between infections and cognitive ability remained significant after adjusting for other factors known to influence a decrease of general cognitive ability, such as gestational age, birth weight [35], and having more older siblings (i.e. being later in a sibship), which often correlate with socio-economic gradients [36]. ..Nevertheless, the findings remained significant also after adjustment for an individual or family history of psychiatric disorders and substance abuse which could be associated with several of these unmeasured risk factors as well as socio-economic factors. Furthermore, the possible effect of maternal smoking during pregnancy should to some degree be captured by the included birth weight and gestational age in the adjustments. Moreover, there may be diseases that are associated with both increased susceptibility to infections and somewhat lower cognition (either the disease itself or its treatment).

BoardsOfCanada 11y ago

The p-value (a function used for testing a statistical hypothesis) corresponding to these results was less than 0.001, indicating that the probability that the findings were due to chance alone (or that the null hypothesis is true) is less than 0.1%. Actually, I think it means that IF the null hypothesis is true, there is only a 0.1% chance that we would get this much deviation (or more) from it due to chance. Which isn't the same thing. Still, seems like a significant result of course, but let's be correct about these things.

axonopathy 11y ago
It looks like the author took this comment to heart.
eru 11y ago
axonopathy, it seems you are hell-banned for some reason..
solve 11y ago
The whole science industry should follow the lead of those scientific journals who've banned p-values from their publications. P-values just lead to so much confusion and nonsense. And that's without even considering the scientists who cheat the p-values, which is actually just a tiny part of the problem with p-values.
- _-__--- 11y ago
  I think that the outright banning of p-values is not the right way to go. The researchers that misuse them and the reviewers that apparently don't understand them are a much bigger problem than the p-value metric itself. What's needed is a better understanding of empirical conditional statistics and the application of that understanding to the degign of experiments and the analysis of the results produced therefrom.
  - solve 11y ago
    And the best way to do that is to eliminate the crutch. Many of the more data-centric fields did away with p-values long ago in favor of far more robust approaches to establishing the value of a paper. Look at papers in the data science field. Using p-values in a paper there would get you laughed out of the industry fast. Only problem that p-values ever solved was allowing journal reviewers to be lazier, helping scientists to be lazier, and making writing more sensational press releases easier.

stefantalpalaru 11y ago

Here's the scientific article: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124005 http://journals.plos.org/plosone/article?id=10.1371/journal....

ExpiredLink 11y ago

It's merely correlation, not causation. P.S.: Why do most articles about the 'brain' try to dumb down people?

danieltillett 11y ago

Interesting study. Intelligence and the immune system share a common property in that they are have a very large number of genes influencing them (several thousand). I would not be surprised if there is quite a bit of overlap in the genes that contibute to both intelligence and immunity. What we might be seeing here is the effect of null mutations in genes that effect both immunity and intellegence.

artnep 11y ago

I've only read the abstract, but it looks like the actual effect isn't huge. People with 10 hospitalizations scored lower by .37 SD = 6 iq points.

felixbraun 11y ago
> Cognitive ability score (Børge Prien’s Prøve Test) has here been converted to parallel conventional IQ scaling, with a mean of 100 and an SD of 15, to give a more familiar metric of effect size. I have no idea what 6 points mean in this setting.
- abandonliberty 11y ago
  I would assume a normal distribution where 68% of the population land between 85 and 115. Or a movement of .4 SD. [0] Nearly 16% of people would lie between 97 and 103. [1] It's 40% of a full letter grade[2] [0]http://en.wikipedia.org/wiki/Standard_deviation http://en.wikipedia.org/wiki/Standard_deviation [1]http://www.wolframalpha.com/input/?i=area+e%5E%28-1%2F450+%28-100%2Bx%29%5E2%29%2F%2815+sqrt%282+%CF%80%29%29%2C+x%3D97+to+103 http://www.wolframalpha.com/input/?i=area+e%5E%28-1%2F450+%2... [2]http://en.wikipedia.org/wiki/Academic_grading_in_the_United_States#Rank-based_grading http://en.wikipedia.org/wiki/Academic_grading_in_the_United_...

Madmallard 11y ago

It's probably not the infection itself, but the fluoroquinolones or other bacteriocidal antibiotics that they give people, that are causing mitochondrial dysfunction in the brain. -_-

gus_massa 11y ago
Never thought bout this, but it's clear that it's possible to have an "antibiotic" that target the mitochondria but leave the rest of the cell alive (for a while). That will be a poison, and be not useful as a actual antibiotic. I there a well know substance like this?

leeleelee 11y ago

This is a premature conclusion. There was no measurement of IQ before and after infection, so no such conclusion can be made. There could be other, unknown, factors that happen to affect BOTH: a person's IQ and their likelihood to be infected, along with severity of infection. For example some genetic, environmental, or other variable that affects your IQ as well as infection-resistance. It very well might be true, that infection does have the ability to lower IQ. But this study does not prove it. I wish scientists would be more straightforward about conclusions. The title of the article should read: "Study finds that individuals who have suffered infection have a lower IQ than the general population" or something along those lines. Much different than saying that "infection lowers IQ". This is beginner-level confusion of causation and correlation.

pdabbadabba 11y ago
The title of the article is, in fact "The Association between Infections and General Cognitive Ability in Young Men - A Nationwide Study." And as others have pointed out elsewhere, the authors controlled for some (though not every) conceivable common causes of infection and reduced IQ. Though, as a criticism of the author of the blog post, I would agree with your comment.
- leeleelee 11y ago
  Ah, you are correct. I missed that.