Taking a multivitamin containing vitamin D may help protect against multiple sclerosis, a new study suggests.

Researchers found women who took vitamin D supplements were less likely to develop MS, a disease that attacks the nervous system. It can cause paralysis and sometimes blindness.

Scientists have known for decades that people who live in cold, dreary climates like Canada's are at higher risk of developing MS.

Dr. Paul O'Conner

They hypothesized that exposure to sunshine, and the higher levels of vitamin D it brings, is somehow protective. Research in animals pointed to a link between vitamin D and MS.

Giving vitamin D to mice with MS makes the disease less severe, said Dr. Paul O'Conner, a neurologist at St. Michael's Hospital in Toronto. "As well, if you give vitamin D to that same animal before it gets the disease it'll prevent MS from happening."

To see if the supplement works in humans, scientists at Harvard School of Public Health in Boston, Mass., looked at data from two studies of more than 180,000 nurses over a 20-year period.

They noticed women who took a daily supplement with at least 400 units of vitamin D were 40 per cent less likely to develop MS than those who didn't take supplements. Other vitamins in the supplement didn't make a statistical difference.

There was no protective effect for women who got their vitamin D from foods such as fortified milk. The study appears in the Jan. 13 issue of the journal Neurology.

The study did not look at whether vitamin D would slow progression of MS in patients who already have the disease. Some are taking the supplement.

"I said this makes sense, it's low cost, it's not going to hurt me," said MS patient Andre Breault, who says he used to avoid the sun religiously.

Vitamin D specialist Reinhold Vietch says most Canadians don't get enough vitamin D, and the recommended daily allowance of 200 units is far too low, given the country's seasons.

"I think dermatologists should be the biggest proponents of vitamin D supplementation," said Vietch, a clinical biochemist at Toronto's Mount Sinai Hospital.

More studies are needed to show conclusively that vitamin D prevents MS. The study's authors suggest measuring vitamin D levels in the blood prior to the onset of MS, for example.

In the meantime, doctors say taking 400 or even up to 2,000 units a day is safe. Other research shows vitamin D may also help rheumatoid arthritis, another autoimmune disease that's more prevalent in cold climates.