For their study, Gocke and her colleagues simultaneously gave mice the rodent form of MS and a high dose of vitamin D and found that the mice showed no symptoms of the disease.

They also found a large number of T cells in the bloodstream of the mice, but very few in their brains and spinal cords.

"Vitamin D doesn't seem to cause global immunosuppression," Gocke said. "What's interesting is that the T cells are primed, but they are being kept away from the places in the body where they can do the most damage."

Gocke added vitamin D may slow a process of making a sticky substance that allows the T cells to grab onto blood vessel walls, which allows the T cells to remain in circulation and keeps them from migrating to the brain.

Once vitamin D is withdrawn, MS-like flare-ups in mice can occur very quickly, the researchers said.

"Vitamin D may be a very safe therapy," said Peter Calabresi, a professor of neurology at Johns Hopkins University and a co-author of the study. "But we still have to be careful with it. It's not just a vitamin. It's actually a hormone."

A clinical trial testing vitamin D supplements in multiple sclerosis patients is underway at Johns Hopkins University, the researchers said.