Objective: In the northern hemisphere, people with anorexia nervosa are more likely to be born in the spring and early summer, particularly when environmental temperature at assumed time of conception is warmer. This study investigates whether there is a comparable effect in the southern hemisphere (Australia), where seasonal and temperature patterns are reversed.
Method: Date of birth and temperature at assumed time of conception were collected for 199 Australian and 259 UK patients with early-onset anorexia nervosa. Analyses determined patterns of birth and links to temperature at conception.
Results: There was little change across the year in the birth patterns of young people with anorexia nervosa in the southern hemisphere. However, there was a significant link between temperature at assumed time of conception and diagnostic subtype. Compared with anorexics of the binge/purge subtype, restrictive anorexics from the southern hemisphere were less likely to be conceived in relatively cool weather.
Conclusions: The findings support a temperature at conception hypothesis (modified for local temperature ranges), rather than suggesting a simple seasonal pattern of birth.