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.”
Telephone: 020 7235 2351 Extensions. 6298 or 6127
Disanto G, Handel AE, Para AE, Ramogopalan SV and Handunnetthi L. Season of birth and anorexia nervosa. British Journal of Psychiatry 2011; 198: 404-405