The weight of arthritis

Obesity is a major modifiable risk factor for osteoarthritis, a progressive joint disease that causes pain and decreased mobility. Osteoarthritis commonly affects the knee, alone or together with other joints. (Photo: UHN)

Researchers at UHN’s Schroeder Arthritis Institute have demonstrated that the relationship between high body mass index (BMI) and hand osteoarthritis may be explained by the presence of osteoarthritis in the knee.

It is well known that individuals who are overweight or obese – those who have a BMI greater than 25 kg/m2 – are more likely to develop osteoarthritis than normal weight individuals of the same age.

Although the negative impact of obesity is most apparent at weight-bearing joints, such as the knee, some studies have linked obesity to osteoarthritis in non-weight-bearing joints, such as the joints of the hand. This finding has led to suggestions that hand osteoarthritis may be linked to body-wide changes that result from being overweight or obese, such as hormone disruptions and inflammation, not just increased stress on joints.

“An issue with a lot of clinical and epidemiological osteoarthritis research is that it treats the disease as though it affects only a single joint,” cautions Dr. Elizabeth Badley, lead author of the study and a Senior Scientist at the Schroeder Arthritis Institute. “In reality, most people with osteoarthritis have symptoms at two or more different joint sites, and this needs to be taken into account in studies of the disease.”

To determine whether the apparent connection between obesity and hand osteoarthritis can be attributed to osteoarthritis at other joint sites, the researchers examined the relationships between BMI and osteoarthritis affecting the hand, hip or knee alone, and combinations of these joints.

Dr. Elizabeth Badley is a Senior Scientist at the Schroeder Arthritis Institute and Director of the Arthritis Community Research and Evaluation Unit. (Image: UHN StRIDe Team)

The research team leveraged the Canadian Longitudinal Study on Aging, which enabled them to analyze data from more than 6,000 individuals with osteoarthritis.

On first impression, high BMI appeared to be linked to a higher likelihood of having osteoarthritis affecting the knee, hip or hand. However, when the researchers examined individuals with all possible combinations of osteoarthritis at these joint sites, they found that BMI was linked only to osteoarthritis in the knee. This relationship was particularly strong for individuals with the highest BMI.

“Taken together, these findings suggest that the previously observed link between high BMI and hand osteoarthritis is likely explained by the presence of the disease at other joints, particularly the knee,” explains Dr. Badley. “The association between high BMI and knee osteoarthritis appears to be distinct from that between high BMI and osteoarthritis in other joints.”

The findings of this study highlight the importance of recognizing the multi-joint nature of osteoarthritis and considering multiple joints when studying the disease.

This work was supported in part by UHN Foundation donors.

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