研究发现，身体质量指数（BMI）与死亡率之间存在J形关联。然而，目前尚不清楚这种关联是否受到偏差的影响，特别是无脂肪体重的混杂作用。我们对153248名韩国成年人（年龄≥40岁）的三个队列进行个人层面的汇总分析。通过2019年12月的随访跟进死亡情况。基线时直接测量了人体测量数据。使用经过验证的预测模型预测脂肪和无脂肪质量。使用Cox比例风险模型，估计BMI和腰围与全因死亡和特定原因死亡的相关性。为了纠正偏差，排除了年龄≥70岁，随访期间死亡时间在5年以内的参与者以及吸烟者，并调整了无脂肪质量指数（FFMI）。在长达18年的随访期间，确认了6061例死亡病例。在没有癌症或心血管疾病史的韩国成年人中，我们观察到BMI的J形关联（22-26为最低点），以及WC与全因死亡、心血管和癌症死亡的单调正相关。在BMI分析中，排除吸烟者和调整FFMI可以减少体重过低参与者的过度死亡率，将J形关联转化为单调的正相关形态，表明BMI>22.0时死亡率增加。排除年龄≥70岁的参与者和随访期间死亡时间在5年以内的病例并不改变结果。在WC分析中，控制后单调的正相关仍然存在。在具有癌症或心血管疾病史的参与者中，观察到类似的结果。我们的数据表明，韩国成年人整体和腹部脂肪都与死亡率增加有关。©作者（2023年）；版权所有，由牛津大学出版社代表国际流行病学协会出版。

Studies found a J-shaped association between body mass index (BMI) and mortality. However, it is unclear whether the association is driven by biases, particularly confounding by fat-free mass.We conducted an individual-level pooled analysis of three cohorts of Korean adults (aged ≥ 40 years; n = 153 248). Mortality was followed up through December 2019. Anthropometric data were directly measured at baseline. Fat and fat-free mass were predicted using validated prediction models. Using Cox proportional hazards models, we estimated the associations of BMI and waist circumference (WC) with all-cause and cause-specific mortality. To account for biases, we excluded participants aged ≥ 70 years, deaths that occurred within 5 years of follow-up and ever smokers, and adjusted for fat-free mass index (FFMI).During the follow-up of up to 18 years, 6061 deaths were identified. We observed J-shaped association of BMI (nadir at 22-26) and monotonically positive association of WC with all-cause, cardiovascular, and cancer mortality among Korean adults without a history of cancer or cardiovascular disease. In the BMI analysis, excluding ever smokers and adjusting for FFMI attenuated the excess mortality in underweight participants and transformed the J-shaped association into a monotonically positive shape, suggesting an increased mortality at BMI > 22.0. Excluding participants aged ≥ 70 years and deaths that occurred within 5 years of follow-up did not change the results. In the WC analysis, the monotonic positive associations did not change after the control. Similar results were observed among participants with a history of cancer or cardiovascular disease.Our data suggest that both overall and abdominal body fat are associated with increased mortality in Korean adults.© The Author(s) 2023; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association.