Vitamin D, which the body makes when exposed to sunlight, may help prevent multiple sclerosis and rheumatoid arthritis, two studies suggest.
The findings may help explain why the two autoimmune diseases are more common in northern climes, where sunlight is often scarce, the researchers said.
In a study released Monday for the Jan. 13 issue of Neurology, the researchers found women who take multivitamins containing vitamin D are 40 percent less likely to develop multiple sclerosis than women who do not take supplements.
“Because the number of cases of MS increases the farther you get from the equator, one hypothesis has been that sunlight exposure and high levels of vitamin D may reduce the risk of MS,” said Kassandra Munger of the Harvard School of Public Health in Boston, who led the study.
“These results need to be confirmed with additional research, but it’s exciting to think that something as simple as taking a multivitamin could reduce your risk of developing MS.”
Multiple sclerosis is a crippling disease caused when the immune system, for unknown reasons, mistakenly damages the myelin, the protective fatty sheath around nerves.
Symptoms range from tremors to paralysis to memory loss and vary from person to person. There are treatments that help, but no cure.
Munger’s team looked at two studies of 187,000 nurses that followed what the women eat and do in their lives, then chronicled their health. Out of all the women, 173 developed MS over a 20-year period.
The nurses with the highest intake of vitamin D from supplements, 400 IU or more a day, were 40 percent less likely to develop MS than those who used no supplements. The women who only got vitamin D from food such as fortified milk did not lower their risk of MS.
A second study, published in the journal Arthritis & Rheumatism, showed that vitamin D may prevent rheumatoid arthritis, another autoimmune disease in which the joints are attacked and destroyed.
The 11-year study of 29,368 women aged 55 to 69 involved detailed questions about eating habits, use of vitamin pills and other lifestyle choices. In this group, 152 women developed rheumatoid arthritis.
The women whose diets were highest in vitamin D had the lowest occurrence of the disease, the researchers at the University of Iowa, the University of Alabama at Birmingham and elsewhere found. Again, supplements seemed to be a better source than food, they reported.
The vitamin may somehow affect the immune system, the researchers said.