Obesity, defined by body mass index (BMI), is a well--established risk factor for atherosclerotic cardiovascular disease, heart failure (HF), and mortality. On the other hand, underweight was also reported to be associated with increased mortality in the general population and in patients with established cardiovascular disease. The controversy regarding the association between BMI and cardiovascular disease or mortality may be dependent on age. Previous studies have shown that the association between obesity and mortality weakens with age, and being underweight is a strong risk factor for mortality in the elderly. In addition to age, the optimal body weight in terms of all-cause mortality has gender differences. However, few studies have explored the effect of age on the association between BMI and cardiovascular events. On May 17, a new large-scale study aiming to investigate whether age modifies the associations of BMI with incident cardiovascular disease or all-cause mortality was published in the European Journal of Preventive Cardiology.
This study utilized data from the Korean National Health Insurance Service (NHIS) database. NHIS provides mandatory health insurance and health examinations for Korean citizens, which allowed to establish a population-based cohort of 9,278,433 Koreans without prior cardiovascular disease who were followed up for the incidence of myocardial infarction (MI), HF, and all-cause death. The effect of BMI with optimal normal weight (18.5–22.9 kg/m2) as reference was analyzed according to age groups [young (20–39 years), middle-aged (40–64 years), and elderly (≥65 years)] and age decades. The authors also investigated whether these associations were modified by sex, smoking status, physical activity level, or abdominal obesity.
During 8.2 years of follow-up, 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 young age, and pre-obesity was associated with the greatest survival benefit. These associations were independent of sex, smoking, physical activity, and comorbidities.
That is, 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.