The small, preliminary study did not look at whether skin rashes, fatigue, fever, and other symptoms of lupus actually improved.
It's too soon to draw any conclusions about vitamin D's long-term safety and effectiveness in treating lupus, says Sam Lim, MD, a rheumatologist at Emory University School of Medicine in Atlanta who was not involved with the work.
Still, vitamin D is one of a number of experimental treatments targeting the disease process that shows promise, he says.
"More and more research is pointing to an immune-regulating role for vitamin D," Lim tells WebMD.
The findings were presented here at the American College of Rheumatology annual meeting.
Race to Develop Targeted Lupus Treatments
About 1.5 million Americans have lupus, a disease in which the immune system attacks healthy tissues, wreaking havoc on the joints, skin, and other organs.
In March, the FDA approved Benlysta, the first new lupus treatment in 50 years. But it only helped about 30% of people in the clinical trials that led to its approval. Benlysta comes with reports of serious side effects, including serious infections.
In people with frequent flare-ups, relatively safe antimalarial drugs or steroids, which can also have serious side effects, are often prescribed. But none of the drugs help everyone.
As a result, the race is on to find new treatments that target specific immune cells involved in causing lupus without harming the rest of the immune system.
Vitamin D Boosts Protective Immune Cells
The new study involved 20 people with no or mild disease activity and low levels of vitamin D.
They were given an injection of 100,000 international units (IU) of vitamin D3 once a week for four weeks. Following that, they received a monthly shot of the same dose of vitamin D for six more months.
The primary goal of the study was to show safety, and that goal was met, says researcher Benjamin Terrier, MD, of the Pitie-Salpetriere Hospital in Paris. The shots were well tolerated, and no one developed too much calcium in their blood or kidney stones, side effects associated with too much vitamin D.
Blood vitamin D levels increased, reaching normal values after two months.
Importantly, vitamin D boosted the number and activity of protective immune cells, he says. And it dampened some abnormal immune cells, calming down the immune system.
Terrier says he believes that if supplementation is stopped, vitamin D levels may drop again, with harm to the immune system.
"We see an initial [immune] signal that looks good for a short period of time. But it's too short and small a study to draw any conclusions about safety and effectiveness," Lim says.
He's particularly concerned about the long-term safety of such high doses of vitamin D. The recommended dietary allowance (RDA) of vitamin D is only 600 IU a day until age 70, he notes.
No one with lupus should try taking high-dose supplements on their own as a way of controlling their disease, Lim stresses.
The next step, Terrier says, will be a larger, longer study comparing vitamin D supplements to a placebo.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.