Association of Body Composition with Disability in Rheumatoid Arthritis: Impact of Appendicular Fat and Lean Tissue Mass

Arthritis Care Research News Alerts. 2008;59(10):1407-1415. 

Body composition in terms of fat and muscle is one of many factors that contribute to limited function in rheumatoid arthritis (RA), a highly inflammatory disease of the joints. Loss of skeletal muscle may lead to a decreased ability to move around and perform manual tasks, while increases in fat mass may lead to greater disability. These changes in body composition have been linked to RA, however, little is known about how they affect disability, which amounts to billions of dollars in direct and indirect costs each year in the U.S.

Body composition is one of the RA factors that can potentially be modified, so interventions to improve it may hold promise for reducing disability and improving quality of life. The first study to explore relationships between body composition and physical functioning in RA patients is published in the October issue of Arthritis Care & Research (

Led by Jon Giles of The Johns Hopkins University School of Medicine, researchers conducted a study on the body composition of 197 patients with RA between the ages of 45 and 84. All subjects underwent a total body dual x-ray absorptiometry (DXA) scanning to analyze and measure fat, lean and bone mass. Disability was assessed in eight categories: dressing, rising, eating, walking, hygiene, reach, grip and errands/chores using the Health Assessment Questionnaire (HAQ). RA status was evaluated by examining 44 joints for swelling, tenderness, deformity and surgical replacement or fusion and disease activity was calculated using C-reactive protein (an indication of inflammation). Patients reported on their pain and overall health and x-rays of the hands and feet were obtained.

The results showed that increasing disability was associated with increasing fat and decreasing lean mass (skeletal muscle), with fat and lean mass on the arms and legs showing the greatest effect. The authors acknowledge that determining factors in the functional capacity of RA patients can be complex, and may be related to the patient's gender, his or her overall level of pain, joint swelling from inflammation, joint deformity and damage, and symptoms of depression. Now the distribution of fat and muscle can be added to that list, which is not surprising, given that good physical function requires muscular strength and physical fitness. As to why increasing amounts of fat, particularly in the arms and legs, should impair physical functioning, the authors propose several theories.

One possibility is that increasing fat may interfere with the normal range of motion of the arms and legs, while another is that fat may somehow biochemically interfere with muscular function. The most likely possibility, however, is that fat may be infiltrating the muscles of those with RA, reducing muscle quality. "Interestingly, in studies of the general population, increasing fat mass has also been more strongly linked to worsening functional capacity than decreasing lean mass, suggesting that efforts to improve physical function require a focus on fat reduction with at least as much emphasis, if not more, than increasing lean mass," the authors note.

The authors plan on conducting further studies to determine whether dietary and/or physical activity intervention may help reduce disability in patients with RA, even if they have inflammation and joint damage. They conclude: "In the absence of interventional trials, these findings suggest that practitioners should encourage muscle strengthening and fat loss in their patients with RA as a method of reducing disability."

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