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 fetus's central nervous system or immune system, and predispose it to developing MS later in life.
In the Australian study, researchers combed birth records of 1,524 MS patients born between 1920 and 1950, and found there were more of them 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 percent higher for those born in the early summer months of November and December compared to the months of May and June," the researchers wrote in a statement.
The research, by Judith Staples and Lynette Lim at the Australian National University in Canberra and professor Anne-Louise Ponsonby at the Murdoch Childrens Research Institute, was published in the British Medical Journal on Friday.
Vitamin D may be particularly important for the development of the fetus's central nervous system, the investigators wrote.
"Vitamin D supplementation for the prevention of multiple sclerosis might also need to be considered during in utero development," they wrote in the paper.
Their findings were 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 — more prevalent in regions that are 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, tremors and an unsteady gait.