Researchers say you can add higher levels of lead in the blood to the list of risk factors for developing knee osteoarthritis (OA).

In a new study, published in the March 2011 issue of Arthritis Research & Therapy, scientists from the Thurston Arthritis Research Center at the University of North Carolina at Chapel Hill analyzed nearly 1,700 rural North Carolinians with and without OA. All participants had lead levels within a normal range. But every one-unit increase of lead levels in the blood translated to 20 percent higher odds that a person had knee OA visible on X-rays – and made it 25 percent more likely that the OA was more severe.

Researchers say lead is potentially toxic to bone and could be contributing to structural damage of the knee through effects on bone and cartilage remodeling.

The blood levels of the North Carolina population study primarily reflected past exposure to lead, before regulatory changes removed it from such commonplace items as gasoline and paint, explains study author Amanda Nelson, MD, an assistant professor at University of North Carolina at Chapel Hill.

But, she adds, “The knowledge that lead levels well below any threshold of toxic exposure are still potentially harmful – associated with high blood pressure, renal disease, and now OA – provides further impetus to continue efforts to reduce population lead levels in the interest of public health.”

Eric Matteson, MD, a consultant in rheumatology at the Mayo Clinic in Rochester, Minn., says this is the first time a lead-OA link has been evaluated this extensively in a large cohort of patients with OA. The findings are interesting, he adds, but he doesn’t believe lead exposure should top the list of concerns when it comes to OA risk.

“The relative contribution of lead levels to development of osteoarthritis is very low, although they did achieve statistical significance,” Dr. Matteson says. “There are many other factors that possibly can contribute to the development of osteoarthritis that the authors recognized, such as body mass index, which have far greater impact on the risk of osteoarthritis. Some of these are difficult to separate from the possible lead effect on the development of osteoarthritis.”

These days, lead can be found in paint in old houses, especially those built or painted before 1955, some cosmetics and toys, and at workplaces where lead is used. Dr. Matteson says people should try to avoid these exposure points, but in the United States, these levels generally are considered very low, and lead exposure has been on the decline.

He believes additional research would be helpful to discover whether these low levels of lead are capable of disrupting cartilage and bone metabolism and function, he adds.