Multiple sclerosis is a disease of the central nervous system in which the specialized lining that surrounds nerve fibers (myelin) is damaged. As a result, nerve impulses cannot be transmitted effectively from one part of the nervous system to another. This leads to a variety of symptoms including numbness, paralysis, and blindness. These symptoms tend to come and go, can range from mild to severe, and can be brief or prolonged. MS is thought to be an autoimmune disorder, meaning that the body's own immune system attacks the nerve cell lining and destroys it.

Genetics, environment, and infections are also suspected of playing a part in the process that starts and/or perpetuates the destructive immunologic response. Because where one lives early in life has been associated with one's risk of MS and because the risk has been seen to increase in parts of the world that receive less sun, a possible role for exposure to sunlight has been the subject of intense research interest.

They concluded that MS risk increased when exposure to sunlight during early pregnancy decreased. This exposure was impacted both by location (distance from the equator) and season (amount of available daily sunlight).

A recent study, published in The British Medical Journal (BMJ) has added to the growing evidence that prenatal sunlight exposure influences a baby's risk of developing multiple sclerosis. The researchers calculated the amount of available ultraviolet radiation by using information about the average amount of sunlight received in different regions of Australia during different months of the year. By knowing where the mother was living during the months of her pregnancy and at the time of delivery they determined how much sunlight exposure a pregnant women and a newborn infant had likely received. They compared this information about 1524 people who had MS to 2,468,779 who did not, who were born in Australia between 1920-1950 and looked at both where they lived and during which months they were pregnant.

They found that the risk of multiple sclerosis was lower for people born closer to the equator and higher for those born farther away. They also found that the risk was highest for those born in the early summer and lowest for those born in the early winter. This corresponded to a higher risk for those whose first trimesters had occurred in winter and a lower risk for the summer. They concluded that MS risk increased when exposure to sunlight during early pregnancy decreased. This exposure was impacted both by location (distance from the equator) and season (amount of available daily sunlight).

Since sunlight acts to produce vitamin D in our skin, the amount of vitamin D available to the developing fetus is thought to be the important factor in changing the risk of developing disease. This suggests that vitamin D supplementation be considered for women whose early trimesters will occur in environments or seasons that are unfavorable for adequate sunlight exposure to produce sufficient vitamin D.

There have been other studies that have linked infant health and positive pregnancy outcomes with maternal exposure to sunlight or maternal vitamin D levels. One study showed an increase in the birth weight of infants whose first trimester occurred during peak sun exposure. Another showed improved bone mineral density in nine years olds whose mothers had high sunlight exposure in the third trimester. Other studies have looked at the role of low maternal vitamin D levels during pregnancy and the risk of neurologic, immune, and mental health disorders. There has also been research at the cellular level that has begun to explore why and how vitamin D affects these diverse functions. Research on animals has shown that maternal vitamin D levels influence the development of nerve tissue in animal fetuses as well as brain development itself.

The investigators also point out that adequate vitamin D throughout the life cycle has potential positive health benefits. Vitamin D deficiency in children and adults is being widely recognized and balancing the role of diet, sunlight, and concerns about the negative health effects of excessive sun exposure is most safely achieved with the counsel of a health care provider. Especially during pregnancy, any changes in diet, vitamins or nutritional supplements, or health habits should be discussed with a physician. Since many women don't seek prenatal care until well into their first trimester, those women who are contemplating pregnancy may benefit from preconception counseling (meeting with a care provider before the pregnancy) to ensure that the earliest weeks of pregnancy are maximally healthy for their growing fetus. For further information about multiple sclerosis, see: