Underweight and mortality

Abstract

OBJECTIVE: According to most prospective studies, being underweight (BMI<18.5 kg/m2) is associated with significantly higher mortality than being of normal weight, especially among smokers. We aimed to explore in a generally lean population whether being underweight is significantly associated with increased all-cause mortality. DESIGN: Prospective cohort study. SETTING: Korea Medical Insurance Corporation study with 14 years of follow-up. SUBJECTS: After excluding deaths within the first 5 years of follow-up (1993-1997) to minimize reverse causation and excluding participants without information about smoking and health status, 94 133 men and 48 496 women aged 35-59 years in 1990 were included. RESULTS: We documented 5411 (5.7 %) deaths in men and 762 (1.6 %) in women. Among never smokers, hazard ratios (HR) for underweight individuals were not significantly higher than those for normal-weight individuals (BMI=18.5-22.9 kg/m2): HR=0.87 (95 % CI 0.41, 1.84, P=0.72) for underweight men and HR=1.12 (95 % CI 0.76, 1.65, P=0.58) for underweight women. Among ex-smokers, HR=0.86 (95 % CI 0.38, 1.93, P=0.72) for underweight men and HR=3.77 (95 % CI 0.42, 32.29, P=0.24) for underweight women. Among current smokers, HR=1.60 (95 % CI 1.28, 2.01, P<0.001) for underweight men and HR=2.07 (95 % CI 0.43, 9.94, P=0.36) for underweight women. CONCLUSIONS: The present study does not support that being underweight per se is associated with increased all-cause mortality in Korean men and women.