A new study in the British Journal of Psychiatry suggests that, of all the factors that lead to eating disorders, at least one may be totally out of our hands: When we were born. Lahiru Handunnetthi at Oxford's Wellcome Trust Centre for Human Genetics and colleagues found that a significantly higher percentage of anorexia patients were born between March and June, while fewer than expected were born in September and October. What might your birthday have to do with developing anorexia nervosa?

What's the evidence?
Handunnetthi's team looked at 1,293 anorexia patients, comparing their birthday patterns to those of the general population. The results provide "clear evidence" that birth season affects anorexia, he said. Among those born in the spring, there were eight cases of anorexia for every seven expected cases. The researchers also noted some anecdotal evidence, says Julie Gerstein in The Frisky: "Several celebrities who have struggled with eating disorders — including Karen Carpenter, Alanis Morissette, and Victoria Beckham — were all born in the spring."

What's the problem with spring births?
It's as much to do with when you were conceived as when you were born, the researchers say. If a woman is pregnant in the fall and winter, she and her developing fetus may not get as much sun and vitamin D, may be exposed to more infections, and may not eat as well, Handunnetthi suggests. Figuring out which factors matter will provide clues to the disorder, and maybe even help prevent it.

Was this a surprise?
Not entirely. Previous, smaller investigations had found possible links between season of birth and eating disorders, but nothing statistically significant. However, "a number of previous studies have found that mental illnesses such as schizophrenia, bipolar disorder, and major depression are more common among those born in the spring," Handunnetthi says.

Is everyone convinced?
No. Anorexia is "a very complex, multifaceted disorder," says Terence Dovey at the Centre for Research into Eating Disorders, Loughborough University. Screening people by season of birth "leaves too much margin of error, and the potential significant difference is only small." Other anorexia specialists recommend that mothers expecting spring babies eat well, don't smoke, and try to avoid getting sick — which is probably good advice, regardless.

Sources: BBC News, Medical News Today, The Frisky, Daily Mail