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.