A prospective study of body mass index and mortality in Bangladesh

Abstract

Background: Body mass index (BMI) (kg/m(2)) has a U- or J-shaped relationship with all-cause mortality in Western and East Asian populations. However, this relationship is not well characterized in Bangladesh, where the BMI distribution is shifted towards lower values.

Methods: Using data on 11,445 individuals (aged 18-75 years) participating in the Health Effects of Arsenic Longitudinal Study (HEALS) in Araihazar, Bangladesh, we prospectively examined associations of BMI (measured at baseline) with all-cause mortality during approximately 6 years of follow-up. We also examined this relationship within strata of key covariates (sex, age, smoking, education and arsenic exposure). Cox proportional hazards models adjusted for these covariates and BMI-related illnesses were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for BMI categories defined by the World Health Organization.

Results: Low BMI was strongly associated with increased mortality in this cohort (P-trend < 0.0001). Severe underweight (BMI < 16 kg/m(2); HR 2.06, CI 1.53-2.77) and moderate underweight (16.0-16.9 kg/m(2); HR 1.39, CI 1.01-2.90) were associated with increased all-cause mortality compared with normal BMI (18.6-22.9 kg/m(2)). The highest BMI category (> or =23.0 kg/m(2)) did not show a clear association with mortality (HR 1.10, CI 0.77-1.53). The BMI-mortality association was stronger among individuals with <5 years of formal education (interaction P = 0.02).

Conclusions: Underweight (presumably due to malnutrition) is a major determinant of mortality in the rural Bangladeshi population.

Figure 1

HRs and 95% CIs for mortality, by BMI categories in the HEALS (Araihazar, Bangladesh). Multivariate estimates were adjusted for age, sex, smoking status, education and BMI-related symptoms experienced in the 6 months prior to baseline (weight loss and weakness). Robust standard errors were used to account for clustering on tube well.

Figure 2

The multivariate-adjusted cumulative hazard function (of mortality) plotted against time (in days) by BMI (kg/m²) category for the HEALS (Araihazar, Bangladesh; n = 11 445). Curves are adjusted to represent non-smoking males (age 18–30 years) with <5 years of formal education (experiencing no weight loss or weakness in the 6 months prior to baseline). Robust standard errors were used to account for clustering on tube well.