A study suggests that people with osteoarthritis who are also obese are three to four times more likely to require knee and hip replacements than those who maintain a normal weight.

A research team at Monash University in Melbourne, Australia followed more than 39,000 healthy volunteers for 15 years and found that increased weight, waist circumference and body mass index (BMI) were associated with a higher risk of joint replacements.

The study’s authors say that the additional weight not only puts stress on joints but that fatty tissues also release inflammatory proteins into the blood that may contribute to the destruction of cartilage.  

For their analysis, researchers stratified study participants into four groups based on their weight. Compared to the lightest group, of women who weighed less than 130 pounds and men who weighed less than 160, those in the heaviest quartile, of women who weighed at least 160 pounds and men who weighed at least 214 pounds, had, on average, 3.4 times the risk of having a knee or hip replaced 15 years after they entered the study.

The association between weight and joint replacements held even when researchers looked at other measures of obesity, like body mass index (BMI) or waist circumference.

Dr. Flavia Cicuttini, a physician in the departments of epidemiology and preventive medicine at Monash University, led the researchers. 

She says these findings have implications for weight loss strategies for people with osteoarthritis. “Weight loss alone may not be sufficient: losing total fat mass as well as decreasing waist fat should be targeted.” 

Lawrence Cheskin, MD, director of the Johns Hopkins Weight Management Center in Baltimore, Maryland, who was not involved in the study, says the report’s finding of a link between a higher BMI and joint replacements is not groundbreaking. But he, too, is intrigued by the research indicating that waist circumference is tied to an increase in joint replacements.

“That seems fairly new to me. The thought that you don’t even necessarily have to be obese,” he explains. He says patients can have a bigger waist circumference without technically being obese. “So the question is, could this be a risk factor independent of being obese if you have extra belly fat.”

Researchers say they expect demand for joint replacement to increase in the future because of the global obesity epidemic. Dr. Cheskin says that is yet another reminder of the benefits of maintaining a health weight.

“I think the bottom line is there is no evidence to the contrary. In other words, losing weight has lots of benefits,” he says. “And you don’t need to be a perfectionist. You don’t have to get to the weight you were at eighteen. Even if you get to a weight that’s half-way to your goal, it may ease your discomfort and the progression of your disease.”

Dr. Cicuttini agrees that regular exercise and avoiding weight gain must be the message. “If people are already obese, it is not too late to change their fate. There is evidence to suggest that weight loss reduces the risk of developing knee osteoarthritis.”

She says she is also planning further studies to try to understand the effect of fat mass on the joint because some of her early work suggests fat may be metabolically active and result in joint damage that could be a possible target for new therapies.