Spring babies face anorexia risk

Embargoed until 28 April 2011

Anorexia nervosa is more common among people born in the spring,
according to
new study published in the May issue of the British Journal
of Psychiatry. The researchers say their study – which is the
largest to date – provides “clear evidence” of a season of birth
effect in anorexia.

The research team, led by Dr Lahiru
Handunnetthi, of the Wellcome Trust Centre for Human Genetics at
the University of Oxford, examined the birth dates of 1,293
patients with anorexia and compared their distribution to the
general population using the Walter and Elwood seasonality test and
Chi Square test. They found an excess of anorexia births between
March and June, and a deficit from September to October.

Although some previous studies have suggested
a link between season of birth and eating disorders, these involved
much smaller numbers of patients and did not reach statistical
significance.

Dr Handunnetthi said: “We meta-analysed four
cohorts of anorexia nervosa patients from the UK, making this the
largest ever study to assess the presence of a season of birth
effect in anorexia. 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.

Dr Handunnetthi said: “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 – so this finding in anorexia is perhaps not
surprising. However, our study only provides evidence of an
association. Now we need more research to identify which factors
are putting people at particular risk.”

The researchers believe that environmental
factors around the time of conception or when the baby is
developing in the womb may be responsible. Dr Handunnetthi said:
“Seasonal changes in temperature, sunlight exposure and vitamin D
levels, maternal nutrition and exposure to infections are all
possible risk factors. Identifying these risk factors is important
in helping us understand and maybe even prevent illness in
future.”