Study illustrates contribution of obesity to decreased mobility in high functioning older women with osteoarthritis

Osteoarthritis, common among older adults, is strongly linked to late-life disability, but the process by which this happens has not been well studied.

A recent study published in the April 2006 issue of Arthritis Care & Research examined the impact of osteoarthritis in the lower extremities and found that women with this condition have a greater risk of developing decreased mobility, a risk which is further increased by being overweight.

Led by Shari M. Ling of Intramural Research Program, National Institute on Aging/NIH together with investigators in the Center on Aging and Health at the Johns Hopkins Medical Institutions in Baltimore, MD, researchers used data obtained from participants in the Women's Health and Aging Study II (WHAS II) to determine whether patients with osteoarthritis in their lower extremities were more prone to developing mobility limitations than women who did not have the disease. They also looked at whether limitations in mobility tended to develop before difficulty in activities of daily living. Their analysis included 199 women with lower extremity osteoarthritis who had no difficulty with mobility tasks at the beginning of the study and 140 women without osteoarthritis in the knee or hip, all of whom were between 70 and 79 years old. Patients were evaluated as to their osteoarthritis status, the presence of pain, knee strength, knee torque, and their level of mobility 18, 36 and 72 months following the initial evaluation.

The results showed that even though more women with osteoarthritis reported using arthritis medications, a greater proportion reported having pain most days and greater pain severity while walking and climbing stairs compared to women with no OA. In addition, 26% of the women with osteoarthritis were obese compared to 11% of the women without the disease, and an additional 40% were overweight. The two groups were similar, however, with regard to knee strength and torque. Overall, women with osteoarthritis were about 2.5 times more likely to develop difficulty in both lower extremity mobility and activities of daily living than those who did not have osteoarthritis. Greater knee strength reduced the risk of developing difficulty performing daily activities whether or not the woman had osteoarthritis, and greater knee torque had the same effect, although it did not reduce the risk for lower extremity difficulty.

"Despite numerous cross-sectional reports of the associations between OA [osteoarthritis], painful symptoms, low strength and obesity, existing studies have not been able to discern the relative contributions of these closely related factors to the development of specific mobility difficulty characteristics," the authors note. The current study demonstrates that lower extremity osteoarthritis is associated with painful symptoms, excess weight and obesity and that women with painful osteoarthritis are more likely to develop lower extremity limitations combined with limitations on their daily activities. The fact that this is affected by higher body mass is what lends novelty to the current study, according to the authors.

"Longitudinal observations of well-functioning women living in the community who are at risk of functional decline provide a unique perspective from which OA can be examined," the authors state. The findings of the current study are particularly relevant given the increase in the number of older Americans and the trend to higher rates of obesity among Americans in all age groups. The authors conclude: "The trends towards earlier onset of obesity observed between 1991 and 1998 would predictably translate into a higher proportion of adults who could develop painful symptoms and mobility difficulty at an earlier age."


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