Body weight and osteoarthritis

BY DAVID HUNTER - MAY 8TH 2015

Osteoarthritis (OA) is a chronic condition of the synovial joint. The disease develops over time and most commonly affects the knees, hips and hands, and less commonly the shoulder, spine, ankles, and feet. It’s a prevalent, disabling disease, and consequently has a formidable individual and social impact. Approximately 10-12% of the adult population have symptomatic OA, and knee OA alone is considered more responsible for increasing the risk of mobility disability (requiring help to walk or climb stairs) than any other medical condition in people aged 65 and over.

Osteoarthritis reduces the quality and quantity of life. By using Quality adjusted life Years (a measure of disease burden taking life quality into account) it can be said that the average, 50-84 year old, non-obese person with knee OA will lose 1.9 years. With obesity, this figure increases to 3.5, and estimated quality-adjusted life expectancy falls by 21% to 25%. Such an impact is similar to that of metastatic breast cancer, showing that OA of any kind should never be underestimated.

Studies like these show the importance of weight control in the management of osteoarthritis. Excess weight burdens weight-bearing joints like the back, hips, knees, ankles and feet, and when applied to joints with OA, increases stress and worsens symptoms. The relationship is also causal in the opposite direction. Abnormal loads on joints overwhelm their capacity for self-repair, and trigger cartilage mechanisms that produce harmful material, which can lead to the joint’s destruction.

While not everyone who has osteoarthritis is overweight, obesity is considered a great risk factor for its development. A body Mass Index of over 30 increases the risk of OA in women by fourfold, and in men by almost 5 times. Researchers have noted the increased risk in obese patients of OA in non-weight-bearing joints, for example, the thumb. Fat cells release molecules causing inflammation in the whole body, affecting all susceptible joints. These molecules not only increase risk of developing OA, but also its severity.

Luckily, even a few kilograms of weight loss can have a beneficial effect. Losing five kilograms has been shown to reduce the risk of developing osteoarthritis by half, and one study showed a 10% body weight reduction can result in up to a 50% reduction in pain. 38% of participants in the same study even reported no pain after they’d taken steps to lose weight.

Many health professionals use the body mass index (BMI in units of kg/m2) to assess patient’s weight, with a BMI of less than 25 indicating a normal weight, 25 to 29.9, overweight, and 30 or above, obese.

The relationship between obesity and osteoarthritis is undeniably complex, varying from patient to patient, but the bottom line is that joints react badly to excess weight. With the number of OA patients expected to double by the year 2020, due in large part to the prevalence of obesity, and the graying of the ‘baby boomer’ generation, OA’s impact on healthcare resources will inevitably increase. Most western countries already spend 1 to 2% of their gross domestic product on arthritis care. The good news, however, even for sufferers of OA, is that positive changes and efforts to lose weight can make an enormous difference to both joint and general health.

Professor David Hunter is a rheumatology clinician researcher whose focus is on clinical and translational research in osteoarthritis. He is Professor of Medicine at University of Sydney, the Florance and Cope Chair of Rheumatology, and staff Specialist at Royal North Shore Hospital, and the North Sydney Orthopaedic and Sports Medicine Centre. He is co-author of Osteoarthritis: The Facts.

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