People with high levels of vitamin D in their blood have shown a lower risk of developing multiple sclerosis, according to results of a Swedish study released Monday.

The new study adds to a growing body of research suggesting a link between vitamin D and MS, an autoimmune disease that affects the brain and spinal cord that is believed to afflict more than a quarter-million Americans. The research will be published in Tuesday's edition of the medical journal Neurology.

Vitamin D is made by the body in response to sun exposure and is found naturally in some foods such as fatty fish. The so-called "sunshine vitamin" is also added to milk and other foods in the U.S., though doctors say it is difficult to get the recommended amount of vitamin D from food alone.

Researchers have speculated that low vitamin D levels increase risk for developing a number of chronic health problems, including diabetes, heart disease, various cancers—and MS.

The new study looked at blood samples collected since 1975 from 164,000 people living in northern Sweden that were taken as part of other health studies. The bulk of the samples came from pregnant women.