The study, published in the U.S. journal JAMA Neurology, found that levels of vitamin D were strongly associated with disease severity and speed of progression in early-stage MS patients.

"Because low vitamin D levels are common and can be easily and safely increased by oral supplementation, these findings may contribute to better outcomes for many MS patients," said lead author Alberto Ascherio, professor of epidemiology and nutrition at the Harvard School of Public Health.

Multiple sclerosis is a central nervous system disease that causes problems with muscle control and strength, vision, balance, feeling, and thinking. The World Health Organization estimated that roughly 2.5 million people in the world have the disease.

The researchers analyzed data from 465 MS patients from 18 European countries, as well as Israel and Canada who enrolled in 2002 and 2003 in a trial looking at the effectiveness of the drug interferon beta-1b in treating the disease.

Vitamin D levels were measured at the onset of their symptoms and at regular intervals over a 24-month period. The results were then correlated with their disease symptoms and progression over a period of five years.

They found that early-stage MS patients who had adequate levels of vitamin D had a 57 percent lower rate of new brain lesions, a 57 percent lower relapse rate, and a 25 percent lower yearly increase in lesion volume than those with lower levels of vitamin D.

Loss in brain volume, which is an important predictor of disability, was also lower among patients with adequate vitamin D levels.

The results suggest that vitamin D has a strong protective effect on the disease process underlying MS, and underscore the importance of correcting vitamin D insufficiency, which is widespread in Europe and the U.S., the researchers said.

"The benefits of vitamin D appeared to be additive to those of interferon beta-1b, a drug that is very effective in reducing MS activity," said Ascherio.

"The findings of our study indicate that identifying and correcting vitamin D insufficiency should become part of the standard of care for newly diagnosed MS patients."