Change in Muscle Strength Explains Accelerated Decline of Physical Function in Older Women With High Interleukin-6 Serum Levels

OBJECTIVES: To test whether accelerated sarcopenia in older persons with high interleukin (IL)‐6 serum levels plays a role in the prospective association between inflammation and disability found in many studies. DESIGN: Cohort study of older women with moderate to severe disability. PARTICIPANTS: Six hundred twenty older women from the Women's Health and Aging Study in whom information on baseline IL‐6 serum level was available. MEASUREMENTS: Self‐report of functional status, objective measures of walking performance, and knee extensor strength were assessed at baseline and over six semiannual follow‐up visits. Potential confounders were baseline age, race, body mass index, smoking, depression, and medical conditions. RESULTS: At baseline, women with high IL‐6 were more often disabled and had lower walking speed. After adjusting for confounders, women in the highest IL‐6 tertile (IL‐6>3.10 pg/mL) were at higher risk of developing incident mobility disability (risk ratio (RR) = 1.50, 95% confidence interval (CI) = 1.01–2.27), disability in activities of daily living (RR = 1.41, 95% CI = 1.01–1.98), and severe limitation in walking (RR = 1.61, 95% CI = 1.09–2.38) and experienced steeper declines in walking speed (P < .001) than women in the lowest IL‐6 tertile (IL‐6 ≤1.78 pg/mL). Decline in knee extensor strength was also steeper, but differences across IL‐6 tertiles were not significant. After adjusting for change over time in knee extensor strength, the association between high IL‐6 and accelerated decline of physical function was no longer statistically significant. CONCLUSIONS: Older women with high IL‐6 serum levels have a higher risk of developing physical disability and experience a steeper decline in walking ability than those with lower levels, which are partially explained by a parallel decline in muscle strength.