Vitamin D may cut MS risk

CHICAGO — The risk of developing multiple sclerosis, one of the more common neurological diseases in young adults, may be significantly reduced with higher blood levels of vitamin D, according to the findings of the first large-scale study of the vitamin and MS.

The study, based on stored blood samples from more than 7 million U.S. military personnel, found that young people who had the highest levels of vitamin D had a 62 percent lower risk of developing MS than people with the lowest level. The report appears in today's Journal of the American Medical Association.

Multiple sclerosis is an autoimmune disorder that causes the disintegration of the protective myelin sheath surrounding nerve cells, leading to gradual loss of function and disability. It affects 350,000 people in the U.S. and 2 million around the world.

The results of the study suggest vitamin D could be used to prevent thousands of cases of a serious, incurable illness, said the study's principal author, Alberto Ascherio, associate professor of nutrition and epidemiology at the Harvard School of Public Health.

"But to know whether that's true or not, we need to do a large, controlled, randomized trial in which some people will get vitamin D and some people will not," Ascherio said.

The main source of vitamin D is sunlight, which stimulates the skin to produce the vitamin. Smaller amounts of the vitamin are found in oily fish such as salmon and in cod liver oil, egg yolks, liver and vitamin D supplements. Milk was fortified with vitamin D in the early 1900s, which ended endemic rickets.

Scientists first linked vitamin D deficiency to MS more than 30 years ago when they noticed the disease was more prevalent in northern latitudes, where sunlight is sparse during winter months.

More recent animal studies have shown that vitamin D injections prevent MS from developing in mice, which can be induced in a laboratory setting to develop the myelin destruction characteristic of multiple sclerosis.

Vitamin D affects almost every type of tissue and is believed to play a major role in keeping the body's immune system on an even keel. Some experts theorize that insufficient vitamin D levels may lead the immune system to malfunction in ways that allow it to attack the body's own tissue. Insufficient vitamin D is a factor in osteoporosis and also has been linked to an increased risk of cancer, chronic pain, high blood pressure and other disorders.

The Harvard study adjusted for the geographic differences in sunlight exposure by comparing vitamin D levels among people living in the same latitudes. Between 1992 and 2004, 257 U.S. Army and Navy personnel were diagnosed with MS. The vitamin D content of their stored blood was compared to the levels in the blood of similar service personnel without MS living in the same latitudes. The findings applied to white service personnel only, as sufficient data were not available for blacks and Hispanics.

Some researchers believe the current recommended daily allowances of vitamin D are probably too low to maintain optimum health. The recommendations are 200 international units for infants, children and adults up to 50 years old; 400 IU for men and women from 50 to 70; and 600 IU for people older than 70.

Vitamin D supplements are generally considered safe except for megadoses, Ascherio said. But a large trial to determine if a severalfold increase in the intake of vitamin D supplements can reduce the risk of MS is needed before recommendations can be made for people to take higher doses of the vitamin, he said.