Research has shown that maintaining enough vitamin D in the body may lower the risk of multiple sclerosis (MS). Several studies have shown that people who get more sun exposure and vitamin D in their diets are less likely to have MS. Taking vitamin D supplements is considered an important way to modify your risk of the disease.

Some studies also suggest that vitamin D may benefit people who already have MS. People who have MS and take vitamin D supplements may have symptoms that aren't as bad as they would be if they didn't take vitamin D. Also, symptoms may occur less often, which may improve quality of life.

Taking vitamin D also may lower the risk of relapse and may decrease new scarring in the nervous system. New scarring can be seen on MRI and are known as radiographic lesions. Taking the supplement also may lengthen the time it takes to progress from relapsing-remitting multiple sclerosis to the secondary-progressive phase. But the evidence isn't conclusive. More research is needed to determine whether vitamin D supplements are helpful. While vitamin D supplements appear to be safe for people with MS, high doses can lead to changes in calcium levels.

MS develops when the immune system attacks the coating that protects the nerve cells, known as myelin. Research suggests that vitamin D has a positive effect on the immune system. Experts need to better understand how vitamin D might affect MS.

There's also an association between sunlight exposure and the risk of MS. Sunlight is the body's most efficient source of vitamin D. The farther away from the equator a person lives, the higher the risk of MS. This suggests that exposure to sunlight may offer protection from MS.

The National Academies of Sciences, Engineering, and Medicine recommends that adults up to age 70 get 600 international units (IU) of vitamin D a day. The recommendation increases to 800 IU a day for adults age 71 and older. The recommendation for people who are pregnant or breastfeeding is 600 IU a day. However, the National Academies of Sciences, Engineering, and Medicine recommends against taking more than 4,000 IU a day.

Research studies have shown that taking 400 IU or more of vitamin D a day lowers the risk of MS in women. But if you're diagnosed with vitamin D deficiency, it may be appropriate to take up to 50,000 IU a week for up to three months. Once you've reached the recommended level of vitamin D, switch to a maintenance dose. The maintenance dose varies but is usually between 2,000 and 5,000 IU a day.

Very large doses of vitamin D over a long period can result in bad side effects. Symptoms include nausea, vomiting, constipation, poor appetite, weakness and weight loss. Very large doses of vitamin D also can lead to high levels of calcium in the blood, which can result in kidney stones.

If you're considering vitamin D to reduce your risk of MS or to help manage MS, talk with your health care provider. Discuss what's safe and helpful for you.