An early post generated some interesting comments. It got me thinking about just how large a part genetics (nature) and environment (nurture) play in eating disorders
I delved into the more recent journals.
The sensible thing to do is to look at twin studies. Ideally, identical twins. This will mean that the influence of genetics is constant.
Ross (2006) looked at the literature on twin studies and found that the level of both identical twins having anorexia was 35%. This is called the concordance rate and means that, if one twin had anorexia, there was a 35% likelihood that the other one would too. He also found that 97% of relatives of these twins do not have the disorder.
If the disorder was purely, or even predominantly, genetic, Ross claims you would expect a concordance rate in excess of 80% and that you would also expect the level of anorexia in relatives to be higher than 3%.
Wade et al. (2007) found that family functioning had a large impact on the differences between discordant twins (ie one has anorexia, one doesn't) with recollection of parental comments about their weight and the amount of food related to the likelihood of developing anorexia. Interestingly, considering the popular image of the mother affecting the onset of the disorder, Wade et al found a quite strong link to paternal protection. (An effect size of 1.6, for the statistically minded.).
An aside to this, the researcher who gave the lecture last week said that he would never start an in-patient treatment program for someone unless it also included a family therapy component. So he clearly thinks environment is critical.
Overall, my view is that, as with so much that is associated with the brain, the true answer will be an interaction between both nature and nurture.
But all genetic? No, I don't think the evidence supports that stand.
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Ross, C.A. (2006). Overestimates of the genetic contribution to eating disorders, Ethical Human Psychology and Psychiatry, 8, (2), 123-131.
Wade, T.D., Gillespie, N., Martin, N.G. (2007) A comparison of early family life events amongst monozygotic twin women with lifetime anorexia nervosa, bulimia nervosa, or major depression. International Journal of Eating Disorders, 40 (8), 679-686.
Just saw a report in NY Times on a study that showed a statistical corrolation between female sex hormones in the womb and anorexia. http://www.nytimes.com/2007/12/11/health/research/11insi.html
ReplyDeleteIt was published in the Dec issue of The Archives of General Psychiatry. Given the huge upswing in hormone disruptors in the food supply, there could be a link.
Were the identical twins reared-apart or together? If they were reared together, could you make an argument that if one twin had anorexia it might act as a signal to the parents to put a lot of effort into preventing anorexia in the other twin? That might deflate the concordance rate a bit...maybe... just to be annoying ;-)
ReplyDeleteHayden: Possibly. But I would like to see the original research. The media is notoriously bad at interpreting scientific papers.
ReplyDeleteMark: As far as I can ascertain they were not reared apart. I suspect sufficient numbers would be difficult to collect - once you allow for the probability of twins, then the probability of being reared apart and then the probability of anorexia. But you are right, it would be nicer, and neater, if possible. But it shouldn't affect the genetic component, which was not as strong as some people suggest.
There are two distinct approaches to family therapy in eating disorders. The old "family systems" approach looked at family dysfunction as causal.
ReplyDeleteThe family therapy now recommended for AN and BN (sometimes called "Maudsley") is almost the opposite. In this approach the illness is believed to be the problem, the family is seen as the best tool to help the patient fight the illness.
This is the same type of family therapy offered to patients with cancer and heart disease and ADHD - help to cope with what is a real organic disease with emotional and cognitive symptoms and impact.
Environment obviously IS a factor in EDs, but it is probably nutritional and even uterine environment more than social or familial.