Low Muscle Mass Ups Risk of Knee OA

by Cooper B. Wilhelm

For years, doctors have been telling people that shedding extra pounds is a good way to curb their risk for osteoarthritis (OA) of the knee. A recent study out of Korea, however, suggests that it’s not that simple. If losing weight means losing muscle mass, it do more harm than good.

Research has long shown that being overweight contributes to OA symptoms. A lot of the focus has been on the extra weight itself. After all, more pounds put more pressure on load-bearing joints, such as the knees and hips, and it seems logical that would contribute to deterioration and damage. However, evidence has been building that adipose tissue (fat) has inflammatory properties, and studies have also linked being overweight to OA in the joints of the hand, where added weight would not necessarily create more biomechanical stress.

To determine the relationship between fat, weight, and OA, researchers looked into a phenomenon called sarcopenic obesity. In sarcopenic obesity, increased body fat is accompanied by low muscle mass (called sarcopenia).

Looking at data from the Fifth Korean National Health and Nutrition Examination Survey, researchers put 2,893 people into one of four categories: People with sarcopenic obesity, people who were obese but not sarcopenic, people who were sarcopenic but not obese, and people who were neither obese nor sarcopenic. Everyone in the study was 50 or older and had undergone dual x-ray absorptiometry (DXA) to determine how much muscle and fat they had, as well as radiographic examination to determine whether they had knee OA.

Researchers found that overall, the people in the study who were just obese weighed about the same as the people in the study who were obese and sarcopenic, and the two groups also had about the same average body-mass index. However, their risks of knee OA were vastly different.

Although people who were just obese were more likely to have knee OA than people who were just sarcopenic, people who were sarcopenic and obese had the highest knee OA rates of all — nearly twice those of people without obesity or low muscle mass. In people 65 or older, the difference was even more pronounced.

The study authors conclude that in addition to weight, body composition may also be an important risk factor for knee OA. Thus, simply losing weight may not be the best strategy for countering the condition. “Individuals with lower body weight may have a higher risk of OA if they have an unfavorable body composition, specifically an elevated fat mass,” the study authors wrote.

While sarcopenia can have many — and multiple — causes, the one way to retain or build muscle is to perform muscle-strengthening exercises.

Last Reviewed January 10, 2013

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Cooper B. Wilhelm is an Editorial Assistant at Arthritis Self-Management.

Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.

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