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Q: I was thinking about taking chondroitin for my arthritis pain. But I recently read it might cause melanoma. Should I avoid it?

A: Chondroitin sulfate is among the most popular supplements in the world. It’s often taken in combination with glucosamine for joint disease. Some take it for prevention, others to treat pain.

And yet, evidence that it actually works at all is limited at best. One review of the evidence suggested that of the few studies of chondroitin that were positive, nearly all were funded by makers of the supplement.

Despite this, millions of people take it, many of my patients swear by it, and the lack of evidence doesn’t seem to be much of a concern to them. A frequent comment I hear is: “Well, I’m not sure if it’s doing much, but it can’t hurt, right?”

A new study suggests that maybe it can.

Researchers publishing in the medical journal Molecular Cell are raising concerns that chondroitin sulfate may encourage the development or recurrence of melanoma, a potentially deadly form of skin cancer.

Here’s what they found:

• The growth of human melanoma cells with a particular mutation (called V600E) that had been grafted onto the skin of mice was promoted when the mice consumed chondroitin sulfate. About half of human melanomas contain this mutation.
• Among mice fed chondroitin sulfate, these melanoma tumors were more resistant to an antitumor drug, vemurafenib, than those without the mutation.

Although this research did not actually study human beings with melanoma, the study authors speculate that for people with precancerous skin growths containing the V600E mutation, taking chondroitin might be a bad idea because it could speed up tumor growth. And if a person had melanoma in the past, taking chondroitin might make recurrence more likely.

More study needed

It’s important to point out that this is preliminary research. Although the tumor cells studied came from humans, a link between chondroitin sulfate use and melanoma in humans has not yet been established.

It’s possible that these results aren’t relevant to actual people: For example, the doses or metabolism of chondroitin sulfate may be so different in humans (vs. mice) that these results do not apply to humans. It is not rare that studies in animals do not translate directly to people.

Here’s my take: This research is quite preliminary, and might turn out to have little relevance to human disease.

But if chondroitin sulfate may promote melanoma growth — and it’s not clear that this supplement is particularly helpful anyway — I’d advise against its use, at least until we know more.

Robert H. Shmerling, M.D., is associate professor of medicine at Harvard Medical School and clinical chief of rheumatology at Beth Israel Deaconess Medical Center in Boston. For additional consumer health information, please visit www.health.harvard.edu.

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