Relationship of Interleukin-6 and Tumor Necrosis Factor- With Muscle Mass and Muscle Strength in Elderly Men and Women: The Health ABC Study

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Abstract
Background. A decline in muscle mass and muscle strength characterizes normal aging. As clinical and animal studies show a relationship between higher cytokine levels and low muscle mass, the aim of this study was to investigate whether markers of inflammation are associated with muscle mass and strength in well-functioning elderly persons. Methods. We used baseline data (1997–1998) of the Health, Aging, and Body Composition (Health ABC) Study on 3075 black and white men and women aged 70–79 years. Midthigh muscle cross-sectional area (computed tomography), appendicular muscle mass (dual-energy x-ray absorptiometry), isokinetic knee extensor strength (KinCom), and isometric grip strength were measured. Plasma levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were assessed by enzyme-linked immunosorbent assay (ELISA). Results. Higher cytokine levels were generally associated with lower muscle mass and lower muscle strength. The most consistent relationship across the gender and race groups was observed for IL-6 and grip strength: per SD increase in IL-6, grip strength was 1.1 to 2.4 kg lower (p < .05) after adjustment for age, clinic site, health status, medications, physical activity, smoking, height, and body fat. An overall measure of elevated cytokine level was created by combining the levels of IL-6 and TNF-α. With the exception of white men, elderly persons having high levels of IL-6 (>1.80 pg/ml) as well as high levels of TNF-α (>3.20 pg/ml) had a smaller muscle area, less appendicular muscle mass, a lower knee extensor strength, and a lower grip strength compared to those with low levels of both cytokines. Conclusions. Higher plasma concentrations of IL-6 and TNF-α are associated with lower muscle mass and lower muscle strength in well-functioning older men and women. Higher cytokine levels, as often observed in healthy older persons, may contribute to the loss of muscle mass and strength that accompanies aging.

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