High Rates of Knee Osteoarthritis May Be Related to Too Little Physical Activity

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A major assumption about knee osteoarthritis is being challenged by the results of a new study.

Medical professionals have long suspected that high numbers of osteoarthritis cases could be blamed on two factors that lead to increased wear and tear on the knee joint. The first factor is an aging population; and the second is increasing obesity levels in modern societies.

A study recently published in Proceedings of the Natural Academy of Sciences, however, suggests that aging and obesity might not have as large of an impact as we thought, and we might need to start looking elsewhere to understand what’s really driving the increase in osteoarthritis.

The study, which examined skeletal remains from the modern and early industrial areas — and some from much earlier — found that even accounting for age and obesity, osteoarthritis of the knee is twice as common today as it was before 1950. That’s a huge increase.

Ian Wallace, a co-author of the study, explained to NPR that he had expected earlier populations of hunter-gatherers and farmers would have had a higher rate of osteoarthritis because of their more physically demanding lifestyles. But what he found was the opposite.

“I was actually extremely surprised to find that [osteoarthritis] is much more common today” than it was in Americans long ago, he says.

So what could be driving the modern increase? We can’t say for sure without further study. But another co-author of the report, Daniel Lieberman, has a theory: physical activity. Rather than too much physical activity leading to wear and tear, though, he suspects the culprit could instead be the especially low levels of physical activity unique to modern lifestyles.

Rheumatologist Dr. Richard Loeser of the Thurston Arthritis Research Center at the University of North Carolina agrees, telling NPR: “Your joints aren’t just like your automobile tires that wear out as you use them.” Because exercise helps nutrients diffuse into cartilage, it helps keep the knee strong and healthy. If cartilage is formed and healthier when you’re younger, then your joints are more likely to be functioning better and have less osteoarthritis when you get older, he explains. Exercise also helps fully grown people. “By strengthening your muscles and by stimulating your cartilage you can still improve the health of your joint.”

Other factors may play a part as well, including dietary choices. But the bottom line is that this study is one more piece in the mounting pile of evidence telling us that exercise and physical activity are important for our overall health and well-being.