In a large study of American adolescents, the AddHealth project, teens who carried the long form of the 5HTTLPR locus were more likely to say they were satisfied or very satisified with their lives (at age 18 to 26). People with two long variants were the most cheerful, with short/long carriers in the middle and short/short being the least so.
The effect was significant controlling for ethnicity (p=0.013), however looking at the data shows that this effect was largely driven by the unhappy teens who reported being "Dissatisfied" or "Neither" on the 5 point scale of life satisfaction - but there were only a small number of these, because the great majority said they were "Satisfied" or "Very Satisfied". Still, there you go.
Incidentally, Neuroskeptic readers may remember AddHealth because of its role in the "black women are ugly" race row from earlier this year.
This study is the latest in a long, long line of attempts to correlate 5HTTLPR with happiness, depression, stress and so on. A few months ago I discussed the history of this busy little gene and covered a meta-analysis of no fewer than 54 papers which claimed that there was indeed a link, with the short allele increasing the risk of depression in response to stressful events.
However many studies failed to find one, and worryingly the three largest studies were all negative which is a classic tell-tale sign of publication bias - maybe people were only bothering to publish smaller studies if they did find a link and hence were "exciting findings". This is quite possible because so many researchers collect DNA as part of psychology studies these days. When the 5HTTLPR story got big (about 5 years ago) I know a lot of people decided to jump on the bandwagon by looking at it in the context of their old data.
Personally I have no idea whether 5HTTLPR is associated with anything. I used to think it probably did, but now I'm just confusion. There have been so many studies and so much inconsistency that it's very hard to know. What worries me is that I'm not sure whether we'll ever get a consensus. We've already had a gigantic study (over 80,000 people) showing no link and many meta-analyses coming to different conclusions.
What will it take to settle the issue? An even bigger study? Would 200,000 people do it? A million? I don't know.
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