collision detection: Does the month of your birth affect your risk of mental illness?

February 22, 2007

Does the month of your birth affect your risk of mental illness?

Does the time of year you're born affect your mental state -- and your potential for developing some form of mental illness? According to this interesting piece in the New Scientist, researchers are beginning to think so. The idea actually goes back all the way to 1929, when the Swiss scientist Moritz Tramer noted that people born in late winter were much more likely to develop schizophrenia later in life; indeed, that correlation has been verified in so many followup studies that one study argued "the increased risk of schizophrenia that comes with a winter birthday is almost twice the increase in risk linked to having a parent or sibling with the disorder."

But assuming the connection is true, why would it occur? The obvious culprit is sunlight, the major time-of-year variable. Since sunlight affects levels of everything from melatonin to vitamin D and various neurotransmitters, these could be causing changes in a pregnant mother that have carryover effects on a fetus and its development.

Obviously, this is pretty subtle stuff, and still pretty conjectural. But one of the more fasinating hypotheses is that one's likelihood of becoming anorexic could be linked to the time of year in which you're born. Here's a longish excerpt:

Beth Watkins, an eating disorder researcher at St George's Hospital Medical School in London, has suggested a more subtle reason for the season-of-birth link to anorexia, which follows a similar pattern to that for suicide. Her idea is not that the seasons cause changes in the fetus, but rather that seasonal effects allow babies vulnerable to the condition to be conceived and born only at certain times of the year. People with anorexia are eight times as likely as the general population to have a parent or sibling with the disorder. Often that relative is the mother, and this got Watkins thinking. Was there something about overly thin mothers that might vary by season? "Their actual fertility is on a knife-edge," she says, and babies born in the months most strongly linked to anorexia were conceived in July to September -- which follow the northern hemisphere's warmest months. Could the higher temperature allow an anorexic mother to conserve just enough energy to tip her into a fertile state?
Watkins and her colleague Kate Willoughby looked at a sample of nearly 400 women in the UK with anorexia and other eating disorders. In the UK, only in the summer months of July and August does the average monthly temperature tend to rise above 15 °C, and in keeping with Watkins's hypothesis, significantly more people with anorexia had been conceived during these warmest months. They then collected data on 200 patients in Australia living in and around Sydney, where average temperatures drop below 15 °C only in the winter months of June, July and August. Sure enough, they found that fewer had been conceived in these cooler months. Finally, they looked at a sample of people with anorexia from Singapore, where the temperature remains constant at over 25 °C all year round. There they found no season-of-birth effect at all.

Intriguing stuff, to be sure. Also check out that chart above: It lets you calculate what sort of disorders are correlated to what parts of the year. Click on here for a larger version!

Posted by Clive Thompson at February 22, 2007 12:14 PM

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Comments

Wait...... dyslexia is a mental illness? I don't know about that.

Posted by: BWJones at February 22, 2007 4:58 PM

Yeah, good point -- it's rarely referred to as an illness, is it? "Learning disability," more precisely, is the way I see it described.

Posted by: Clive at February 22, 2007 7:25 PM

So where do you have to live for this to be right?

After having my boyfriend leave me a week before what you posted as the worst day of the year, you now tell me I'm oh, rather likely to develop schizofrenia? Yikes, reading this blog is getting risky.

Thank God I'm a hot chick with superpowers.

Posted by: eke at February 23, 2007 4:22 AM

Superpowers! It sounds like this research is mostly European, so I'm suspecting that chart applies to folks living in mid-northern climes.

Posted by: Clive at February 23, 2007 12:06 PM

What about microbes? I believe that their presence/absence is seasonal. In my physiological psych class (circa 1989), my prof displayed the seasonal fluctuations in the incidences of several viruses and then the seasonal fluctuations in the number of births where the child goes on to develop schizophrenia. It looked like a correlation could have been made. He conjectured that early fetal development might be hampered by a virus but in non-obvious ways, laying the groundwork for the development of later problems.

I also came across a newsitem that grew out of the correlation between the presence of cats in a household where a child who later developed schizophrenia was born. Apparently there is a link. The author suggested that microbes associated with cats or cats' faeces could contribute to problems with the developing child. And the microbes would have the seasonally-fluctuating occurence mentioned above. The author noted that schizophrenia seems only to have become frequent in Europe and N.America since the industrial revolution and the adoption of cats as housepets rather than professional rat killers around the farm.

All speculations and correlations, but there ya go.

Erik

Posted by: Cultureraven at February 27, 2007 7:22 AM

Sounds like this idea could be used to explain other date/characteristics correlation’s such as the Horoscope. Although absolutely no evidence exists to prove the horoscope, and therefore I am incredibly sceptical, I have to admit my Libra tag fits me very well. ....Just sayin’.

Posted by: Flyingbiscuit at February 27, 2007 11:59 AM

Er, the website from which you posted the chart (http://www.thecivicplatform.com) is a white supremacist loony farm. Just sayin'.

Posted by: Mark Lerner at February 27, 2007 3:14 PM

There is a study quoted in this month's Economist that talks about the specious nature of this kind of statistical research [article here http://www.economist.com/science/displaystory.cfm?story_id=8733754, study abstract here http://tinyurl.com/2lwd8s].

In a study of all 10 million+ residents of Ontario, they discovered that "Residents born under Leo had a higher probability of gastrointestinal hemorrhage..., while Sagittarians had a higher probability of humerus fracture."

Their conclusion: "Our analyses illustrate how the testing of multiple, non-prespecified hypotheses increases the likelihood of detecting implausible associations."

Posted by: vespaboy at February 27, 2007 11:45 PM

Their conclusion: "Our analyses illustrate how the testing of multiple, non-prespecified hypotheses increases the likelihood of detecting implausible associations."

Posted by: vespaboy at February 27, 2007 11:46 PM

There is a study quoted in this month's Economist that talks about the specious nature of this kind of statistical research (article here http://www.economist.com/science/displaystory.cfm?story_id=8733754, study abstract here http://tinyurl.com/2lwd8s).

Their conclusion: "Our analyses illustrate how the testing of multiple, non-prespecified hypotheses increases the likelihood of detecting implausible associations."

Posted by: vespaboy at February 27, 2007 11:47 PM

(Sorry for the triple-post -- the form wasn't working properly and I guess I got overzealous. F^%$ing newbie.)

Posted by: vespaboy at February 28, 2007 3:22 PM

So if I'm reading this correctly, because my birthday is in September, I am more likely to have both panic disorder and alcoholic tendencies?

Really, don't they just kind of cancel each other out? I find that a good stiff drink cures my anxieties.

Posted by: Scott at March 5, 2007 1:24 PM

The NYT also notes that star soccer players are more likely born earlier in the year, so they can be the most mature players in youth leagues. http://www.nytimes.com/2006/05/07/magazine/07wwln_freak.html?ex=1304654400&en=2cf57fe91bdd490f&ei=5090&partner=rssuserland&emc=rss

Posted by: Glenn Kelman at March 10, 2007 12:10 AM

Hah! That's great. I love it that August and January are totally risk free. I know a few people who kinda prove that wrong ...

Posted by: Rebecca Skloot at March 17, 2007 12:43 AM