CHICAGO — An abundance of vitamin D seems to help prevent multiple sclerosis, according to a study in more than 7 million people that offers some of the strongest evidence yet of the power of the "sunshine vitamin" against MS.

The research found that white members of the U.S. military with the highest blood levels of vitamin D were 62 percent less likely to develop multiple sclerosis than people with low levels.

There was no such connection in blacks or Hispanics, possibly because there were so few in the group studied. Also, the body makes vitamin D from sunlight, and the pigmented skin of blacks and other dark-skinned ethnic groups doesn't absorb sunlight as easily as pale skin.

The new research echoes findings in smaller studies that examined why the nerve-damaging disease historically has been more common in people who live in regions farther from the equator where there is less intense year-round sunlight.

"This is the first large prospective study where blood levels are measured in young adults and compared to their future risk. It's definitely different and much stronger evidence," said Dr. Alberto Ascherio, the senior author and an associate professor of nutrition at Harvard's School of Public Health.

The study appears in a recent Journal of the American Medical Association.

"If confirmed, this finding suggests that many cases of MS could be prevented by increasing vitamin D levels," Ascherio said.

Still, he said the findings don't prove that a lack of vitamin D can cause MS.

Vitamin D also is found in fortified milk and oily fish, but it's hard to get enough just from diet. Sunlight is the biggest source of vitamin D, which is needed for strong bones. Other studies have linked high levels of vitamin D in the blood to lower risks of a variety of cancers.