Tuesday, 18 December 2007
A relook at eating disorders.
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.
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.