Department of Medicine, Albert Einstein College of Medicine, Bronx, NY, United States of America.
Department of Epidemiology & Population Health, Albert Einstein College of Medicine, Bronx, NY, United States of America.
PLoS One. 2018 Apr 11;13(4):e0194697. doi: 10.1371/journal.pone.0194697. eCollection 2018.
The level of body-mass index (BMI) associated with the lowest risk of death remains unclear. Although differences in muscle mass limit the utility of BMI as a measure of adiposity, no study has directly examined the effect of muscle mass on the BMI-mortality relationship.
Body composition was measured by dual-energy x-ray absorptiometry in 11,687 participants of the National Health and Nutrition Examination Survey 1999-2004. Low muscle mass was defined using sex-specific thresholds of the appendicular skeletal muscle mass index (ASMI). Proportional hazards models were created to model associations with all-cause mortality.
At any level of BMI ≥22, participants with low muscle mass had higher body fat percentage (%TBF), an increased likelihood of diabetes, and higher adjusted mortality than other participants. Increases in %TBF manifested as 30-40% smaller changes in BMI than were observed in participants with preserved muscle mass. Excluding participants with low muscle mass or adjustment for ASMI attenuated the risk associated with low BMI, magnified the risk associated with high BMI, and shifted downward the level of BMI associated with the lowest risk of death. Higher ASMI was independently associated with lower mortality. Effects were similar in never-smokers and ever-smokers. Additional adjustment for waist circumference eliminated the risk associated with higher BMI. Results were unchanged after excluding unintentional weight loss, chronic illness, early mortality, and participants performing muscle-strengthening exercises or recommended levels of physical activity.
Muscle mass mediates associations of BMI with adiposity and mortality and is inversely associated with the risk of death. After accounting for muscle mass, the BMI associated with the greatest survival shifts downward toward the normal range. These results provide a concrete explanation for the obesity paradox.
与最低死亡率相关的身体质量指数（BMI）水平仍不清楚。尽管肌肉量的差异限制了 BMI 作为肥胖衡量标准的效用，但尚无研究直接检查肌肉量对 BMI 与死亡率关系的影响。
通过 1999-2004 年全国健康和营养调查（NHANES）的 11687 名参与者的双能 X 射线吸收法测量身体成分。使用四肢骨骼肌指数（ASMI）的性别特异性阈值定义低肌肉量。创建比例风险模型来对与全因死亡率相关的关系进行建模。
在任何 BMI≥22 的水平下，肌肉量低的参与者体脂肪百分比（%TBF）较高，糖尿病的可能性增加，且死亡率高于其他参与者。%TBF 的增加表现为与保留肌肉量的参与者相比，BMI 变化小 30-40%。排除肌肉量低的参与者或调整 ASMI 会减弱与低 BMI 相关的风险，放大与高 BMI 相关的风险，并将与死亡率最低相关的 BMI 水平向下转移。较高的 ASMI 与较低的死亡率独立相关。在从不吸烟者和曾吸烟者中，效果相似。进一步调整腰围消除了与较高 BMI 相关的风险。在排除意外体重减轻、慢性疾病、早期死亡以及进行肌肉强化运动或达到推荐体力活动水平的参与者后，结果保持不变。
肌肉量介导 BMI 与肥胖和死亡率的关联，并且与死亡风险呈负相关。在考虑肌肉量后，与最大生存相关的 BMI 向下移向正常范围。这些结果为肥胖悖论提供了一个具体的解释。
