The notion that the wear and tear of running causes arthritic knees and ankles is not backed up by studies. (Bigstock)

While out on a run recently, I passed a hiker on the trail. “My knees hurt just watching you,” he told me, shaking his head. It was a variation on a comment I hear over and over: Keep running like that, and you’ll give yourself arthritic knees.

The notion that running causes wear and tear on the joints that could spur arthritis makes some intuitive sense. But is it true?

No — if anything, running probably offers protection from osteoarthritis, says Paul Williams, an exercise scientist at Lawrence Berkeley National Laboratory who leads the National Runners’ Health Study and the National Walkers’ Health Study. These projects have enlisted almost 90,000 runners and walkers and followed them since the studies began, in 1991 and 1997, respectively. In an analysis recently published in the journal Medicine & Science in Sports & Exercise, Williams calculated rates of osteoarthritis and hip replacement among participants in his studies and found that runners were approximately half as likely as walkers to develop osteoarthritis or need a hip replacement. Furthermore, runners who ran the most had the lowest risk of osteoarthritis.

“There’s a perception out there that somehow you’re wearing out your joints if you’re out there running,” Williams says, but the thousands of runners in his study show this just isn’t so. “I’ve recruited people who were doing 60 or 70 miles per week, and we’ve followed them over time,” he says. “If there had been an effect, we would have seen it.”

The notion that running causes osteoarthritis arises from a misperception about how joints work, says Alex Hutchinson, a science journalist who is author of the Sweat Science blog at Runner’s World and the book “Which Comes First, Cardio or Weights? Fitness Myths, Training Truths, and Other Surprising Discoveries from the Science of Exercise.” “People think the joint is just a static, inert hinge that wears down, but it’s actually a dynamic, living thing that can respond to stress and adapt and get stronger,” he says. Rather than wear down cartilage and other joint tissue, running appears to strengthen them, Hutchinson says.

The latest research shows that osteoarthritis isn’t just a result of wear and tear on your joints, says Patience White, vice president for public health policy and advocacy at the Arthritis Foundation. Instead, the disease arises from an interplay between environment and genetics. The strongest risk factors for osteoarthritis are obesity and family history, says White, who is also a professor or medicine and pediatrics at the George Washington University School of Medicine and Health Sciences.

Every extra pound you carry is akin to four pounds on your knees, White says: “If you lose five pounds, that’s like 20 pounds across your knees.” But obesity’s role in osteoarthritis isn’t confined to the extra stress it can put on joints. “People who weigh more also get more osteoarthritis in their wrists, so it’s not just about mechanical loading through the joint,” Hutchinson says. Fat tissue is metabolically active and secretes inflammatory hormones that interact with everything in the body, including cartilage and joints, he says.

Family history is another predictor of osteoarthritis, and researchers have identified several genes associated with a susceptibility to the disease. “If you have osteoarthritis in your family, you’re more likely to get it no matter what you do,” White says.

This sounds like bad news for me, since osteoarthritis runs in my family, and my dad recently had a hip replacement because of the disease. But White says I can delay or perhaps even prevent getting osteoarthritis by staying active and keeping my weight in check. Running accomplishes both.

Still, it’s important to run wisely, White says. If you try to go from the couch to a marathon without putting in the necessary training, you’re liable to get hurt. Injury ups the risk of osteoarthritis, although developing the disease takes the kind of traumatic injury that tears ligaments or tendons — problems that more commonly occur in sports that involve contact or require sudden changes in direction. Such injuries increase osteoarthritis risk by promoting abnormal mechanics or by creating scarring that can strain the joint, White says, and an injury can deliver a double whammy by forcing a decrease in physical activity that leads to weight gain.

More than 50 percent of people who have a serious knee injury such as a ligament or tendon tear will develop osteoarthritis within 10 years, White says. “If you’ve had a bad knee injury at age 15, chances are you’ll have osteoarthritis at 25.”

While running wasn’t associated with osteoarthritis in the Williams study, other types of exercise, such as soccer and hockey, were linked with a greater risk of developing the disease. “We’re trying to pursue that further,” Williams says.

Given that other activities seem to increase osteoarthritis risk, why does running get a bad rap? Some of it may be schadenfreude, Hutchinson says. “Every time a runner gets osteoarthritis in their knee, all their friends and family say, ‘See? I told you you shouldn’t have run. You did this to yourself,’ ” he says. “But when five non-runners get osteoarthritis, people just say, ‘Well, I guess you’re getting old.’ ”

I am getting older, and even after decades of running, my knees feel better now than they did when I was 20. I hope I never have to quit trail running, and Williams says that if I keep at it, chances are good that I won’t have to stop anytime soon.