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.