"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 study author Kassandra Munger, MSc, of Harvard School of Public Health in Boston, MA. "This is the first prospective study to look at this question.
"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."
The researchers examined data from two large studies involving women, the 20-year Nurses' Health Study and the 10-year Nurses' Health Study II. The women's diets and use of multivitamin supplements were assessed as the studies began and then again every four years. Women with MS symptoms starting before beginning the study were not included in the results. There were 187,563 women in the study. Of those, 173 women developed MS during the course of the study.
The women were divided into groups based on vitamin D use. Those with the highest intake of vitamin D from supplements (400 IU or more per day) were 40 percent less likely to develop MS than those who used no supplements.
The risk of developing MS was lower both for those high in intake of vitamin D from supplements only and for those high in intake from both supplements and food. However, those whose intake of vitamin D was from food only did not have any lesser risk of developing MS.
The researchers also analyzed the data while adjusting for smoking and latitude at birth, but the results did not change.
Since supplemental vitamin D intake was mainly from multivitamins, it is difficult to isolate the effects of vitamin D from the potential effects of other vitamins found in multivitamins, according to Munger.
"However, none of these vitamins was itself significantly associated with risk of MS after adjusting for total vitamin D intake or vitamin D from supplements," Munger said.
Earlier research also points to the role of vitamin D in MS. Studies with mice with experimental autoimmune encephalomyelitis (EAE), an autoimmune disease in animals that is used as a model of MS, have shown that vitamin D supplements can prevent or favorably affect the course of the disease. Other studies have shown that people with MS tend to have insufficient levels of vitamin D, and that periods of low vitamin D occur before times of high disease activity, and periods of high vitamin D precede times of low disease activity.
Munger said that future prospective studies should measure the levels of vitamin D in the blood prior to the onset of MS.
The study was supported by grants from the National Institutes of Health.
The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, autism and multiple sclerosis.
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