Children whose mothers had low exposure to sunlight during their first three months of pregnancy may have a higher risk of developing multiple sclerosis later in life, a study in Australia has found.
Low vitamin D levels have long been linked to a higher risk of MS. Experts suspect an expectant mother's lack of exposure to sunlight - the main source of vitamin D - may affect the foetus's central nervous system or immune system, and predispose it to developing MS later in life.
The research, by Judith Staples and Lynette Lim of the Australian National University in Canberra and Professor Anne-Louise Ponsonby of the Murdoch Childrens Research Institute, appears in the British Medical Journal.
In the study, researchers combed birth records of 1524 MS patients born between 1920 and 1950, and found there were more born in the months of November and December.
This means their first trimester occurred during the winter months of April to June, a time when expectant mothers in the southern hemisphere may prefer to be indoors to escape the cold.
Conversely, there were far fewer MS patients who were born in May and June - meaning their first trimesters were in the early summer months of September to November.
"The risk of multiple sclerosis was around 30% higher for those born in the early summer months of November and December compared to the months of May and June," the researchers write.
They add, vitamin D may be particularly important for the development of the foetus's central nervous system.
"Vitamin D supplementation for the prevention of multiple sclerosis might also need to be considered during in-utero development."
Their findings are supported by previous studies conducted in the northern hemisphere, which found more cases of MS among people born in May, whose mothers probably had little exposure to sunlight in their first trimester during the colder months of September to November.
MS, which is more prevalent in regions further away from the equator, can cause permanent disability with symptoms such as numbness or weakness in one or more limbs, partial or complete loss of vision, tremours and an unsteady gait.
According to the Murdoch Childrens Research Institute it affects an estimated 18,000 people in Australia.