Our aim was to investigate whether there is a season-of-birth effect in
anorexia nervosa. In a meta-analysis, we compared the distribution of
anorexia births (n = 1293) from four independent UK cohorts
to that of the general UK population (n = 21 914 037),
using both the Walter & Elwood seasonality and chi-squared tests. We
found an excess of anorexia births from March to June (odds ratio (OR) =
1.15, 95% CI 1.03–1.29, P = 0.012) and a deficit from
September to October (OR = 0.8, 95% CI 0.68–0.94, P =
0.007). These results indicate that environmental risk factor(s) are
operative during gestation or immediately after birth and their
identification will be important for disease prevention strategies.