Losing excess weight may not only help prevent knee arthritis, but also slow its progression in people who already have the condition, a recent study suggests.
Researchers found that among over 9,000 middle-aged and older adults, those who managed to shed some extra weight benefited their knees in two ways: They were less likely to develop knee arthritis over the next several years; and if they already had knee arthritis, the joint damage progressed more slowly.
It has long been known that excess pounds are a risk factor for developing knee arthritis. And when people with the condition are overweight or obese, they are encouraged to lose weight to help ease their pain.
Experts said the new findings suggest that weight loss may not only curb pain, but also help protect the integrity of the knee joint itself.
"Even in overweight and obese patients who already have some structural knee osteoarthritis damage, there is still a role for weight loss in preventing further harm," said Dr. Emily Carroll, a rheumatologist with the Mount Sinai Health System in New York City.
Dr. Linda Russell, a rheumatologist at the Hospital for Special Surgery, also in New York City, agreed.
"There's no doubt that when you have knee osteoarthritis and you lose weight, you'll have less pain," Russell said. "This suggests that losing weight also slows the progression of the joint damage."
The findings — from a team at the University of New South Wales in Australia — are not particularly surprising, according to Russell. In basic terms, excess weight places more pressure on the knees, especially the medial (or inner) side of the joint. In this study, Russell noted, weight changes were specifically related to the odds of joint space narrowing on the inner side of the knee.
"So this is confirming what we've suspected," she said.
But that confirmation is important, Russell added, since it may give patients more motivation to shed extra pounds.
"If you have knee osteoarthritis and lose weight, you might be able to either avoid knee replacement surgery or delay it," Russell said.
One point, though, is that it did take substantial weight loss to make a major difference. On average, the study found, people had to drop a whole body mass index (BMI) category — going from obese to overweight, for example — to reduce the odds of arthritis progression by 22%.
That is challenging, according to Russell. "The hard part is, patients with knee osteoarthritis often find it difficult to exercise because of pain," she said.
Still, both doctors said, there are low-impact forms of exercise that get the heart pumping and burn calories — like swimming, walking, cycling and using elliptical machines.
"I do encourage patients to find activities they can do, and that they enjoy," Russell said.
The Australian study included nearly 5,800 adults who were free of knee osteoarthritis, and just over 6,000 who already had the disease. Osteoarthritis refers to the common, "wear-and-tear" form of arthritis that involves a breakdown in the cartilage that cushions joints.
Overall, the study found, about one-fifth of participants managed to lower their BMI over four to five years. (BMI is an estimate of body fat based on height and weight.)
For each "unit" decrease in BMI, the risk of developing knee arthritis dipped by 5%, and the risk of further joint damage declined by a similar amount. When people with knee arthritis had a BMI decline of 5 units — enough to drop down to a new BMI category — their risk of progression decreased by 22%, the investigators found.
But while lesser weight loss brought a smaller benefit, it still matters, according to Carroll. "Every bit does count," she said.
To both lose weight and keep it off, Carroll noted, exercise is only part of the equation: Healthy eating habits that can be kept up for the long haul are key.
Both doctors recommended that people with knee arthritis talk to their health care providers for help with weight loss: Some might benefit from physical therapy to help them get active. And some, depending on their BMI and other health conditions, might qualify for weight-loss treatments.
The findings were recently published online in the journal Arthritis & Rheumatology. Lead author Zübeyir Salis is a doctoral candidate at the University of New South Wales, in Australia.
The Arthritis Foundation has more on knee osteoarthritis.
SOURCES: Emily Carroll, MD, internal medicine, rheumatology, Mount Sinai Health System, New York City; Linda Russell, MD, director, perioperative services, Hospital for Special Surgery, assistant professor, medicine, Weill Cornell Medical College, New York City; Arthritis & Rheumatology, Aug. 16, 2022, online