Pattern of birth in anorexia nervosa. I: Early-onset cases in the United Kingdom.

Objectives: Previous studies suggest that adults with anorexia nervosa are more likely to be born in spring and early summer. This study examines whether this pattern of birth is true of early-onset anorexia nervosa, and whether there is a relationship between environmental temperature at assumed time of conception and a later diagnosis of anorexia nervosa.

Method: The population were children and adolescents with diagnoses of anorexia nervosa (N = 259) or "other eating disorders" (N = 149). Distribution of births across the year was compared between groups and relative to standard population norms. Temperature at assumed time of conception was taken from meteorological records.

Results: There was a significant preponderance of births among those with anorexia nervosa between April and June, compared with the other months of the year and with the "other eating disorders" group. Anorexia nervosa was also associated with higher environmental temperature at assumed time of conception.

Conclusions: Among early-onset cases in the United Kingdom, patients with anorexia nervosa are more likely to be born between April and June, and to be conceived during warmer months. A tentative "temperature at conception" hypothesis is advanced to explain these findings and to generate further research.