Taking daily vitamin D supplements does not reduce the pain of knee osteoarthritis, or OA, and it does not slow the disease’s progression, according to a study presented at a meeting of the American College of Rheumatology Annual Scientific Meeting.

“I think there’s a high level of enthusiasm for vitamin D currently. People think it will help in many medical areas,” says lead investigator Timothy McAlindon, MD, a professor of medicine in the division of rheumatology at Tufts New England Medical Center in Boston.

However, when it comes to the vitamin’s effect on knee OA, the recent findings are “not what we had hoped to have seen,” Dr. McAlindon says.

OA, the most common form of arthritis, is marked by the degeneration of cartilage in and around joints, which causes pain that can severely limit people’s mobility.

Vitamin D is needed to properly absorb calcium. If you aren’t getting enough of it – by absorbing it through sunlight, taking supplements or getting it from foods like oily fish, fortified milk, eggs and cheese – your bones can become weak and fracture. Some earlier studies have indicated that vitamin D helps slow the progression of knee OA, but those findings weren’t supported in this latest study conducted by researchers at Tufts New England Medical Center.

“There have been some observational studies looking at vitamin D levels and knee OA. At the time we started this study there were only one or two and they were positive. During the course of our study, others came out that were more negative,” Dr. McAlindon says. “My assumption was that [vitamin D] would work, but the body of evidence changed from being positive to more negative.”

Dr. McAlindon and his research team studied 146 people – mostly white women, with an average age of 62 – who had symptomatic and radiographic knee OA. Researchers split participants into two groups. One group took vitamin D every day, starting with a dose of 2,000 IU, which was increased as needed for patients to reach levels of 30 ng/ml or higher. The other group took a placebo. For all participants, researchers measured pain, physical function, damage visible through X-rays and damage visible on MRIs at the start of the study and one year later.

When the study ended, the group taking supplements had higher vitamin D levels than the placebo group, but “we found really no significant differences in any [OA-related] outcomes between the two groups,” Dr. McAlindon says.

He says that for now, these results should only be applied to people who represent the study sample, as more research is needed to confirm the findings. And he points out that supplemental vitamin D has other benefits, such as improving bone health.

“The osteoporosis physicians are recommending vitamin D. So if people take vitamin D for that reason, nothing needs to change,” Dr. McAlindon says. “If they are taking it for osteoarthritis, they should probably talk to their doctors.”

Katherine Temprano, MD, is an assistant professor of internal medicine in the division of rheumatology at Saint Louis University. She says you could argue, given this study’s limited sample, that more research is needed to look at males and different ethnicities. But she also says this is a very well done and important study.

“There was a definite need to do this. There have been multiple studies that have found a low serum level of vitamin D has been associated with OA, particularly of the knee but other joints too,” Dr. Temprano says. “So you would think that if you took more vitamin D that you might be able to inhibit the disease progression. That had not really been effectively looked at before.”

Still, she recommends people taking vitamin D continue to do so because, as a rheumatologist, she’s always concerned about bone quality.

“We know that for osteoporosis and osteopenia that you do need adequate vitamin D supplementation,” Dr. Temprano says. “So it doesn’t mean you shouldn’t take your vitamin D supplements by any means. It’s just that osteoarthritis is a separate disease and so it may not be the treatment or cure-all for OA, but it still has many other roles for bone health.”