Season of birth bias in eating disorders--fact or fiction?

OBJECTIVE A season of birth (SoB) bias is said to be present if the SoB pattern for a particular group varies from the pattern within the normal population. Significant biases have been found for several disorders including eating disorders (EDs). This article critically reviews the existing literature on SoB in ED in order to inform future hypothesis-based research. METHOD A literature search identified 12 papers investigating SoB in ED. RESULTS Despite methodological differences, the studies consistently show a SoB bias for anorexia nervosa (AN) in the spring months, in both the northern and southern Hemispheres. This is especially strong for early-onset and restrictive subtype of AN. CONCLUSION These findings suggest that SoB is a risk factor for AN. However, none of the studies have been methodologically satisfactory. Future research needs to overcome numerous methodological challenges and to explore specific hypotheses to explain this bias.