month of birth

You might have heard that individuals born between the months of June – August (or sometimes March – August) have a higher chance of developing anorexia nervosa. But is it true? A lot of studies have been done to investigate the question of whether a season of birth (or a month) correlates with a higher risk of anorexia or bulimia nervosa. The results are inconsistent, weak, and fraught with methodological problems.

But first, how could seasons (or the average temperature during birth, or conception) have an effect on the etiology of eating disorders? What’s the hypothesis?

There seem to be two main ideas (summarized in Winje et al., 2012):

1. alterations in neuropsychological function as a result of sunlight exposure during gestation or postpartum, maternal infections during pregnancy, or nutritional changes (seasonal variation in nutrients, vitamins)
2. alterations in fertility/reproductive patterns of the parents due to cultural influences, disordered eating in the