Handgrip strength and cause-specific and total mortality in older disabled women: Exploring the mechanism

OBJECTIVES: To examine the association between muscle strength and total and cause-specific mortality and the plausible contributing factors to this association, such as presence of diseases commonly underlying mortality, inflammation, nutritional deficiency, physical inactivity, smoking, and depression. DESIGN: Prospective population-based cohort study with mortality surveillance over 5 years. SETTING: Elderly women residing in the eastern half of Baltimore, Maryland, and part of Baltimore County. PARTICIPANTS: Nine hundred nineteen moderately to severely disabled women aged 65 to 101 who participated in handgrip strength testing at baseline as part of the Women's Health and Aging Study. MEASUREMENTS: Cardiovascular disease (CVD), cancer, respiratory disease, other measures (not CVD, respiratory, or cancer), total mortality, handgrip strength, and interleukin-6. RESULTS: Over the 5-year follow-up, 336 deaths occurred: 149 due to CVD, 59 due to cancer, 38 due to respiratory disease, and 90 due to other diseases. The unadjusted relative risk (RR) of CVD mortality was 3.21 (95% confidence interval (CI) = 2.00-5.14) in the lowest and 1.88 (95% CI = 1.11-3.21) in the middle compared with the highest tertile of handgrip strength. The unadjusted RR of respiratory mortality was 2.38 (95% CI = 1.09-5.20) and other mortality 2.59 (95% CI = 1.59-4.20) in the lowest versus the highest grip-strength tertile. Cancer mortality was not associated with grip strength. After adjusting for age, race, body height, and weight, the RR of CVD mortality decreased to 2.17 (95% CI = 1.26-3.73) in the lowest and 1.56 (95% CI = 0.89-2.71) in the middle, with the highest grip-strength tertile as the reference. Further adjustments for multiple diseases, physical inactivity, smoking, interleukin-6, C-reactive protein, serum albumin, unintentional weight loss, and depressive symptoms did not materially change the risk estimates. Similar results were observed for all-cause mortality. CONCLUSION: In older disabled women, handgrip strength was a powerful predictor of cause-specific and total mortality. Presence of chronic diseases commonly underlying death or the mechanisms behind decline in muscle strength in chronic disease, such as inflammation, poor nutritional status, disuse, and depression, all of which are independent predictors of mortality, did not explain the association. Handgrip strength, an indicator of overall muscle strength, may predict mortality through mechanisms other than those leading from disease to muscle impairment. Grip strength tests may help identify patients at increased risk of deterioration of health.