Season of birth and bulimia nervosa

OBJECTIVE: Previous studies suggest season of birth variation in eating disorders akin to those of psychoses. We studied season of birth variation in bulimia nervosa. METHOD: Season of birth variation in 935 patients was examined after adjustment for population trends. Variation was also examined for subgroups by age and previous anorexia nervosa. RESULTS: Season of birth did not differ significantly from population norms among bulimics (p >.30), contrasting with studies of other eating disorders. With a history of anorexia nervosa (n = 227), peak season of birth was in March (p <.05). This is consistent with previous studies and also with seasonal birth variation for psychoses. DISCUSSION: Overall, we find no evidence of season of birth variation in bulimia nervosa, and suggest any positive findings be treated with caution. We discuss a number of confounding influences and argue that one explanation remains shared trait vulnerability between anorexia nervosa and psychoses.