Muscle Strength and Body Mass Index as Long-Term Predictors of Mortality in Initially Healthy Men

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Abstract
Background. Muscle weakness, low body weight, and chronic diseases are often observed in the same people; however, the association of muscle strength with mortality, independent of disease status and body weight, has not been elucidated. The aim was to assess hand grip strength as a predictor of all-cause mortality within different levels of body mass index (BMI) in initially disease-free men. Methods. Mortality was followed prospectively over 30 years. Maximal hand grip strength tests and BMI assessments were done at baseline in 1965 to 1970. The participants were 6040 healthy men aged 45 to 68 years at baseline living on Oahu, Hawaii. Results. The death rates per 1000 person years were 24.6 in those with BMI <20, 18.5 in the middle BMI category, and 18.0 in those with BMI ≥25. For grip strength tertiles, the mortality rates were 24.8 in the lowest, 18.5 in the middle, and 14.0 in the highest third. In Cox regression models, within each tertile of grip strength, BMI showed only minimal effect on mortality. In contrast, in each category of BMI there was a gradient of decreasing mortality risk with increasing grip strength. Among those with BMI <20, the adjusted relative risks (RRs) of mortality over 30 years were 1.36 (95% confidence interval 1.14–1.63) for those in the lowest third of strength at baseline, 1.27 (1.02–1.58) in the middle, and 0.92 (0.66–1.29) in the highest third. Correspondingly, for those with BMI 20–24.99, the RRs of death were 1.25 (1.08–1.45), 1.14 (1.00–1.32), and 1.0 (reference) in the lowest, middle, and highest third of grip strength, respectively. In those with BMI ≥25, the RRs were 1.39 (1.16–1.65) in the lowest, 1.27 (1.08–1.49) in the middle, and 1.14 (0.98–1.32) in the highest third of grip strength. Models were adjusted for age, education, occupation, smoking, physical activity, and body height. Conclusions. In healthy middle-aged men, long-term mortality risk was associated with grip strength at baseline, independent of BMI. The possible interpretation of the finding is that early life influences on muscle strength may have long-term implications for mortality. Additionally, higher strength itself may provide greater physiologic and functional reserve that protects against mortality.