WEDNESDAY, Dec. 30, 2015 (HealthDay News) -- High-dose vitamin D appears safe for people with multiple sclerosis, and it may help quiet the immune system hyperactivity that marks the disease, a small clinical trial finds.
The study, published online Dec. 30 in Neurology, bolsters evidence that vitamin D might benefit people with MS.
But clinical trials are still underway to answer the big question: Does taking vitamin D improve MS symptoms and alter the course of the disease?
The current study shows only that high doses -- 10,400 IU a day -- reduce the proportion of certain immune-system cells that have been implicated in the MS disease process.
"I'm not going to make any claims beyond that," said senior researcher Dr. Peter Calabresi, a professor of neurology at Johns Hopkins University in Baltimore.
"We don't have enough data here to guide clinical practice," he stressed.
Bruce Bebo, executive vice president of research for the National Multiple Sclerosis Society, echoed that caution.
"This study was not designed to look at efficacy against MS. It was too small and too short to do that," said Bebo, whose group helped fund the research.
Still, Bebo added, the findings are important for other reasons. For one, he said, "they give us some hints about the mechanisms that explain the higher MS risk associated with low vitamin D."
MS is caused by an abnormal immune system attack on the protective sheath surrounding nerve fibers in the brain and spine. That leads to symptoms such as muscle weakness, numbness, vision problems, and difficulty with balance and coordination.
Typically, MS symptoms flare up periodically, followed by periods of remission. Over time, the disease can cause worsening problems with walking and mobility.
The precise cause of MS is unknown, but researchers believe it involves a combination of genetic vulnerability and certain environmental triggers. Inadequate vitamin D -- a nutrient needed for normal immune function -- is considered one of the suspects.
That's partly based on studies showing an association between blood levels of vitamin D and the risk of developing MS. But there is also more-direct evidence, Bebo said. For example, research has shown that vitamin D can reduce the effects of an MS-like disease in lab mice.
The new findings suggest it may alter immune system activity in people with MS, too, Bebo said.
According to Calabresi, the results underscore another point: High doses of vitamin D are probably necessary.
His team tested two doses in 40 adults with MS. Over six months, one group took 10,400 IU of vitamin D a day -- about 17 times the amount that the U.S. government recommends for healthy adults (600 IU a day); the other group took 800 IU a day.
In the end, only the high-dose group showed changes in their immune system activity. The largest effect, Calabresi said, was a reduction in cells that produce an inflammatory protein called interleukin-17.
However, the study looked only at certain aspects of immune function. And MS is a "complicated disease immunologically," Calabresi noted.
He said it will be interesting to see whether vitamin D has additional immune system effects in people with MS, or possibly other autoimmune diseases.
Several clinical trials are now testing vitamin D against MS, including a U.S. study that's still recruiting patients. The trials are using doses ranging from 5,000 to 10,000 IU a day, Calabresi said.
Without those trial results, he said, it's too early to recommend that people with MS take vitamin D.
But, he added, since adequate vitamin D is important for overall health, people may want to be tested for deficiency in the nutrient.
With vitamin D supplements readily available, Calabresi also recognized that some people with MS will probably start taking it even in the absence of proof.
He encouraged them to use vitamin D only under medical supervision.
In this study, high doses appeared safe over six months. But, Calabresi said, high blood levels of vitamin D can send blood calcium concentrations soaring, which can cause kidney stones or other problems, such as poor appetite, weakness and constipation.
Bebo agreed. "Always speak to your [doctor] about any medications or supplements that you're thinking of taking," he said.
The National Multiple Sclerosis Society has more on the possible causes of MS.