OBJECTIVES We examined the dose-response relationships of body composition indices with mortality and identified the best predictor. DESIGN AND SETTING Kusatsu Longitudinal Study and Hatoyama Cohort Study, Japan. PARTICIPANTS In total, 1977 community-dwelling Japanese adults age ≥65 years (966 men and 1011 women) participated. MEASUREMENTS Body mass index (BMI), fat mass index (FMI), fat-free mass index (FFMI), and skeletal muscle mass index (SMI) were determined by segmental multifrequency bioelectrical impedance analysis. The main outcome was all-cause mortality. We determined multivariate-adjusted hazard ratios for mortality relative to sex-specific medians of each body composition index and examined the association shapes. RESULTS During the median follow-up of 5.3 years, 128 (13.3%) men and 75 (7.4%) women died. Compared with median BMIs (23.3 kg/m2 in men and 22.8 kg/m2 in women), a BMI >23.3 and ≤26.1 kg/m2 was associated with significantly lower mortality risk in men, and a BMI <22.8 kg/m2 was associated with significantly higher mortality risk in women. The inverse dose-response relationship with mortality was clearer for FFMI [hazard ratios (95% confidence interval) of 10th and 90th percentiles: 1.58 (1.23-2.03) and 0.58 (0.44-0.79), respectively, in men and 1.56 (1.12-2.16) and 0.68 (0.51-0.91), respectively, in women] and SMI [1.57 (1.22-2.01) and 0.60 (0.45-0.80), respectively, in men and 1.45 (1.05-2.01) and 0.77 (0.61-0.96), respectively, in women] than for BMI [1.30 (0.92-1.83) and 0.65 (0.41-1.03), respectively, in men and 1.87 (1.18-2.95) and 0.88 (0.54-1.42), respectively, in women]. FMI was not associated with mortality in either sex. CONCLUSIONS AND IMPLICATIONS FFMI and SMI were more definitive predictors of mortality than were BMI and FMI. The lower mortality risk with higher FFMI, regardless of FMI, may explain the age-related weakening of the association between higher BMI and mortality (the "obesity paradox"). FFMI and SMI evaluation should be introduced to clinical assessments of older adults because mortality risk might be reduced by maintaining muscle mass.

中文翻译：

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日本老年人身体成分指数与全因死亡率之间的剂量反应关系

目标我们检查了身体成分指数与死亡率的剂量反应关系，并确定了最佳预测指标。设计和设置草津纵向研究和鸠山队列研究，日本。参与者 总共有 1977 名年龄≥65 岁的社区居民日本成年人（966 名男性和 1011 名女性）参与。测量 身体质量指数 (BMI)、脂肪质量指数 (FMI)、无脂肪质量指数 (FFMI) 和骨骼肌质量指数 (SMI) 通过分段多频生物电阻抗分析确定。主要结果是全因死亡率。我们确定了死亡率相对于每个身体成分指数的性别特异性中位数的多变量调整风险比，并检查了关联形状。结果 在中位随访 5.3 年期间，128 名（13.3%）男性和 75 名（7.4%）女性死亡。与中位数 BMI (23. 男性 3 kg/m2 和女性 22.8 kg/m2），BMI > 23.3 且≤ 26.1 kg/m2 与男性死亡风险显着降低相关，BMI <22.8 kg/m2 与死亡风险显着升高相关在女性中。对于 FFMI [第 10 个和第 90 个百分位数的风险比（95% 置信区间）：男性分别为 1.58 (1.23-2.03) 和 0.58 (0.44-0.79) 和 1.56 (1.12- 2.16) 和 0.68 (0.51-0.91)，女性] 和 SMI [1.57 (1.22-2.01) 和 0.60 (0.45-0.80)，男性和 1.45 (1.05-2.01) 和 0.77 (0.96)分别在女性中] 比 BMI [男性分别为 1.30 (0.92-1.83) 和 0.65 (0.41-1.03)，女性分别为 1.87 (1.18-2.95) 和 0.88 (0.54-1.42)]。FMI 与两种性别的死亡率均无关。结论和意义 FFMI 和 SMI 是比 BMI 和 FMI 更明确的死亡率预测因子。无论 FMI 是什么，FFMI 越高，死亡风险越低，这可能解释了 BMI 与死亡率之间的相关性随着年龄而减弱（“肥胖悖论”）。FFMI 和 SMI 评估应引入老年人的临床评估，因为通过保持肌肉质量可能会降低死亡风险。