Lack of ambient sunshine during pregnancy linked to MS risk

The risk of developing multiple sclerosis (MS) later in life is higher for children born in November-December compared with those born May-June, according to a new Australian study.
The results are consistent with previous research that found a reciprocal pattern in the northern hemisphere, where there were more cases of multiple sclerosis among people born in May and fewer in those born in November.

According to background information in the study, low vitamin D levels have been linked with a higher risk of MS. The researchers suspect that variations in exposure to sunlight during pregnancy may influence the development of the central nervous system or immune system and determine the risk for MS in adult life.
Researchers analysed data on the number of patients with multiple sclerosis born in Australia compared to other births for each birth-month of every year, from 1920 to 1950, by sex and region of birth.
They used the large regional and seasonal variation in ambient ultraviolet radiation in Australia to explore the relation between a mother’s exposure to ambient ultraviolet radiation during pregnancy and subsequent risk of multiple sclerosis in their offspring. They found that the risk of MS was around 30 per cent higher for those born in the early summer months of November and December compared to the winter months of May and June.
No association between daily ultraviolet radiation levels at the time of birth (or one to four months before birth) and subsequent risk of multiple sclerosis was found. However, maternal exposure to low ultraviolet radiation levels between five and nine months before birth predicted a higher risk of multiple sclerosis. This effect persisted after adjustment for region of birth and appeared more important than the month of birth.
Region of birth was also related to risk, suggesting that offspring postnatal exposure to sunlight during childhood and early adulthood is also important.
These findings clearly show that region of birth and low maternal exposure to ultraviolet radiation in the first trimester are independently associated with subsequent risk of multiple sclerosis in offspring in Australia, the study’s authors concluded.
The team also recommended that vitamin D supplementation during pregnancy be evaluated as a means to help prevent multiple sclerosis.
BMJ Online, available at http://www.bmj.com/cgi/doi/10.1136/bmj.c1640