Risk of Anorexia Greater For Those Born in Spring

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Why would being born in spring increase one’s risk of anorexia? Scientists are not certain, but the results of a new study offer evidence of an association between anorexia risk and when people are born.

Causes of anorexia are unknown

An estimated 0.5 to 3.7 percent of women will suffer from anorexia nervosa at some point during their lives, according to the US National Institute of Mental Health and other statistics, and about 0.3 percent of men may develop this eating disorder as well.

The causes of and risk factors for anorexia, which has one of the highest mortality rates of any mental illness, are unknown, although a number of possibilities have been proposed, including genetics, brain dysfunction, neurotransmitter imbalance, maternal depression, societal pressure to be thin, poor self-esteem, perfectionism, and childhood abuse, among others.

A new study from researchers at the Wellcome Trust Centre for Human Genetics, University of Oxford, proposes that the time of year when someone is born may predispose him or her to develop anorexia. The authors say theirs is the “largest study to date” on this question, as previous studies have included too few subjects.

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Investigators gathered data, including birth dates, on 1,293 people with anorexia and found that a greater number than normal (15% excess) were born between March and June, while fewer than expected (20% deficit) were born in September and October. According to the lead investigator, Dr. Lahiru Handunnetthi, “we found that susceptibility to anorexia nervosa is significantly influenced by a person’s season of birth, being higher in those people born in the spring and lower in those born in the autumn.”

Other studies have indicated that when a person is born may play a role in the development of mental disorders. A new study from Wright State University and published in Medical Hypotheses, for example, notes that season of birth may be a factor in schizophrenia, with people born in the spring and fall seeming to be at higher risk.

In addition, Dr. Handunnetthi noted that other mental illnesses, such as major depression and bipolar disorder, “are more common among those born in the spring—so this finding in anorexia is perhaps not surprising.” The question, however, is why season of birth could have such an impact, and the study’s authors ventured several possibilities.

Dr. Handunnetthi explained that environmental factors could play a part. “Seasonal changes in temperature, sunlight exposure and vitamin D levels, maternal nutrition and exposure to infections are all possible risk factors.” The challenge now is to identify the factors that can explain why the risk of anorexia is greater for people who are born in the spring.

SOURCES:
Oxford University
Schwartz P. Medical Hypotheses 2011 Mar 5

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