Age-dependent associations of body mass index with myocardial infarction, heart failure, and mortality in over 9 million Koreans

AIMS: While obesity is a well-known cardiovascular risk factor, little is known whether age has a modifying effect. The aim of this study is to determine the age-dependent associations of body mass index (BMI) with cardiovascular outcomes. METHODS AND RESULTS: A population-based cohort of 9 278 433 Koreans without prior cardiovascular disease were followed up for the incidence of myocardial infarction (MI), heart failure (HF), and all-cause death. The effect of BMI with optimal normal weight (18.5-22.9 kg/m2) as reference was analysed according to age groups young (20-39 years), middle-aged (40-64 years), and elderly (≥65 years) and age decades. During 8.2 years, MI, HF, and all-cause death occurred in 65 607 (0.71%), 131 903 (1.42%), and 306 065 (3.30%), respectively. Associations between BMI and all outcomes were significantly modified by age (P-for-interaction < 0.001). There was a proportional increase in incident MI according to BMI in young subjects; this relationship became U-shaped in middle-aged subjects and inversely proportional/plateauing in elderly subjects. A U-shaped relationship between BMI and incident HF was observed, but the impact of obesity was stronger in young subjects while the impact of underweight was stronger in middle-aged and elderly subjects. Meanwhile, lower BMI was associated with higher all-cause mortality in all ages, although this association was attenuated at the young age, and pre-obesity was associated with the greatest survival benefit. These associations were independent of sex, smoking, physical activity, and comorbidities. CONCLUSION: The impact of BMI on cardiovascular risk differs according to age. Weight loss may be recommended for younger overweight subjects, while being mildly overweight may be beneficial at old age.