The timing of birth may increase the risk of developing multiple sclerosis (MS) with people born in May most at risk, research published today shows.
The study, which included over 42,000 patients with MS from Canada, the UK, Denmark and Sweden, found the month of birth and the risk of developing MS are associated, especially where there is a family history of the condition.
Published in the British Medical Journal on-line edition today, the research sought to determine if the risk of MS is associated with the month of birth in countries in the northern hemisphere and if factors related to month of birth interact with genetic risk.
It is already known that susceptibility to MS is influenced by genetic and environmental factors. An association with latitude has also been shown in migrants from regions of differing risk. However, this new study shows that in northern countries the risk of MS is greater for people born in May and is lowest for those born in November. The study found the effect to be greater in Scotland where the population prevalence of MS is the highest.
These findings support suggestions from previous studies in twins and half-siblings that environmental factors both before and immediately after birth alter the risk of MS in later life. Commenting on the results, the authors note that the May/November birth ratio in MS sufferers living in the northern hemisphere may "hold the key to disease prevention".