Winter 2016

Do Your Knees Need D?

Vitamin may protect your joints from arthritis

By Jacqueline Mitchell

People who are lacking in vitamin D could be doubling their risk for progressive osteoarthritis, the cartilage-eroding joint disease that leads to achy knees and mobility problems.

Fang Fang Zhang, an assistant professor of epidemiology at the Friedman School, and her colleagues tracked 418 people who already had some evidence of knee osteoarthritis, which affects as many as 50 percent of adults at some point, according to the Arthritis Foundation. They discovered a relationship between low blood levels of vitamin D and osteoarthritis that worsened over time.

300W Knee

Arthritis of the knee. Photo: © Dr. P. Marazzi,

The observational study, published in the Journal of Nutrition, included patients who had complained of knee pain, or whose X-rays showed early signs of the disease. Zhang and her colleagues examined subsequent X-rays taken over the course of four years to determine whether the osteoarthritis got worse. The researchers also monitored the patients’ blood levels of vitamin D.

The researchers saw “almost double the risk of progression in people with low vitamin D levels compared with those with adequate vitamin D status,” says Zhang.

Zhang saw the doubling of risk only in people who were clinically deficient in vitamin D, so she emphasizes her findings don’t mean that everyone should start taking supplements. “When we see a positive association like this, people tend to get all excited,” she says. “But only people with vitamin D deficiency would benefit—not everyone.”

Zhang’s observational study follows a clinical trial conducted by Tim McAlindon, a professor of medicine at Tufts, and Bess Dawson-Hughes, M75, a senior scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts. That two-year study of 146 people sought to determine whether vitamin D supplementation could halt or actually reverse the progression of osteoarthritis of the knee. The researchers found no evidence to support that; their findings were published in the Journal of the American Medical Association in 2013.

But that doesn’t mean the two studies contradict each other.

McAlindon says that a limitation of his clinical trial “is that for ethical reasons, we could not enroll people who are medically deficient in D, so none of the participants was really deficient. Therefore, we couldn’t rule out the possibility that people who are extremely deficient in D might experience some benefit from vitamin D.”

Jacqueline Mitchell can be reached at

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