Age-dependent relationships between body mass index and mortality: Singapore longitudinal ageing study

OBJECTIVES: The relationship between body mass index (BMI) with mortality risk, in particular the BMI category associated with the lowest all-cause and CVD-and-stroke mortality and the BMI threshold for defining overweight or obesity in older persons is controversial. This study investigated the age-dependent associations of BMI categories with all-cause and cardiovascular disease (CVD) and stroke mortality. METHOD: Prospective cohort study (Singapore Longitudinal Ageing Studies) of older adults aged 55 and above, followed up from 2003 to 2011. Participants were 2605 Chinese with baseline BMI and other variables. Outcome Measurement: Mortality hazard ratios (HR) for all-cause and CVD and stroke mortality. RESULTS: Overall, BMI showed a U-shaped relationship with all-cause and CVD and stroke mortality, being lowest at Normal Weight-II category (BMI 23.0–24.9 kg/m2). Most evidently among the middle-aged (55–64 years), all-cause mortality risks relative to Normal Weight-II were elevated for underweight (<BMI 18.5; HR = 4.92, p<0.0138), Normal Weight-I (BMI 18.5–22.9; HR = 3.41, p = 0.0149), and Overweight-Obese (BMI>30.0; HR = 4.05,p = 0.0423). Among the old (≥65 years), however, Overweight and Obese categories were not significantly associated with increased all-cause mortality (HR from 0.98 to 1.29), but Overweight-Obese was associated with increased CVD and stroke mortality (HR = 10.0, p = 0.0086). CONCLUSION: BMI showed a U-shaped relationship with mortality. Among older persons aged 65 and above, the overweight-or-obese category of BMI was not associated with excess all-cause mortality.