Correcting vitamin D deficiency early in the course of the disease is important, according to the report, published online Jan. 20 in JAMA Neurology.
But some experts say it's too soon to recommend giving vitamin D supplements to people with the central nervous system disorder.
"No one knows what the connection between MS and vitamin D is," said Nicholas LaRocca, vice president for health care delivery and policy research at the National Multiple Sclerosis Society. "What they suspect is that vitamin D has some effect on the immune system."
Also, what dose of the vitamin might be appropriate isn't clear, he said. "We don't know what a good level would be. There is no scientific consensus on a treatment protocol. We may get to that point eventually," LaRocca said.
However, the lead researcher of the study, Dr. Alberto Ascherio, a professor of epidemiology and nutrition at the Harvard School of Public Health, is convinced that vitamin D -- often called the "sunshine vitamin" -- can be a real benefit to MS patients.
"These findings, combined with previous evidence that vitamin D deficiency is a risk factor for MS, and [research on] the immunological effects of vitamin D strongly suggest that maintaining an adequate vitamin D status is important in the treatment of MS," he said.
In the study, vitamin D levels at the time of the first MS symptoms predicted the progression of the disease over the following five years, Ascherio said.
People with lower vitamin D levels -- below 50 nanomoles per liter (nmol/L) -- were more likely to develop new brain lesions and had a worse prognosis than those with higher levels, Ascherio said. "Individuals who present with symptoms suggesting MS should be screened for possible vitamin D deficiency, and this should be corrected by vitamin D supplementation," he said.
MS is a chronic, debilitating disease. In many cases, symptoms are mild, but sometimes people with MS become unable to walk, write or speak.
Dr. Emmanuelle Waubant, director of the Regional Pediatric MS Center at the University of California, San Francisco, is among those urging caution regarding vitamin D supplementation.
"Although these data are exciting, these are just studies of association," Waubant said. "We still need to do a randomized clinical trial of vitamin D supplementation to confirm that supplementation improved MS outcomes."
Another expert agreed.
"The results are exciting because they confirm our own prior work," said Dr. Ellen Mowry, an assistant professor of neurology at Johns Hopkins University School of Medicine in Baltimore.
However, she added that no study has yet established whether taking vitamin D supplements helps reduce new symptoms and disability from occurring in people with MS. "It's possible that the effects we have seen in this and the prior studies are actually due to something else, and not to vitamin D insufficiency," she said.
Also, even though vitamin D is sold over the counter, it doesn't necessarily mean it's safe to take a lot. "Like any medication, it may have negative effects of which we are not aware," Mowry added.
Vitamin D is also obtained from sunlight and through certain foods, such as fatty fish and fortified dairy products.
Mowry and Waubant are heading up a large clinical trial of vitamin D in MS patients. Similar trials are underway in Europe and Australia, Waubant noted.
"It is my belief that these trials will help answer the important question of whether it is safe and effective to recommend high-dose vitamin D supplementation to people with MS," Mowry said.
For the study, researchers measured vitamin D levels in 465 patients with signs of MS who took part in a trial designed to study interferon beta-1b treatment. For the next five years, patients underwent MRI scans so the researchers could track brain lesions associated with the disease.
During the first year of follow-up, increases of 50 nmol/L of vitamin D were associated with a 57 percent lower risk of developing new brain lesions, the study findings showed.
In addition, patients had a 57 percent lower risk of relapse, the researchers found. They also had a 25 percent lower yearly increase in T2 lesion size (these hallmarks of MS appear as bright spots on an MRI) and a 0.41 percent lower yearly loss in brain size over the course of the study.
For more information on multiple sclerosis, visit the National Multiple Sclerosis Society.