Sex-specific associations between body mass index and death before life expectancy: a comparative study from the USA and Sweden

Abstract

Background: Understanding the impact of obesity on premature mortality is critical, as obesity has become a global health issue.

Objective: To contrast the relationship between body mass index (BMI) and premature death (all-cause; circulatory causes) in New York State (USA) and Northern Sweden.

Methods: Baseline data were obtained between 1989 and 1999 via questionnaires (USA) and health exams (Sweden), with mortality data from health departments, public sources (USA) and the Swedish Death Register. Premature death was death before life expectancy based on sex and year of birth. Within country and sex, time to premature death was compared across BMI groups (18.5-24.9 kg/m² (reference), 25-29.9 kg/m², 30.0-34.9 kg/m², ≥35.0 kg/m²) using Proportional Hazards regression. Absolute risk (deaths/100,000 person-years) was compared for the same stratifications among nonsmokers.

Results: 60,600 Swedish (47.8% male) and 31,198 US subjects (47.7% male) were included. Swedish males with BMI≥30 had increased hazards (HR) of all-cause premature death relative to BMI 18.5-24.9 (BMI 30-34.9, HR = 1.71 (95% CI: 1.44, 2.02); BMI≥35, HR = 2.89 (2.16, 3.88)). BMI≥25 had increased hazards of premature circulatory death (BMI 25-29.9, HR = 1.66 (1.32, 2.08); BMI 30-34.9, HR = 3.02 (2.26, 4.03); BMI≥35, HR = 4.91 (3.05, 7.90)). Among US males, only BMI≥35 had increased hazards of all-cause death (HR = 1.63 (1.25, 2.14)), while BMI 30-34.9 (HR = 1.83 (1.20, 2.79)) and BMI≥35 (HR = 3.18 (1.96, 5.15)) had increased hazards for circulatory death. Swedish females showed elevated hazards with BMI≥30 for all-cause (BMI 30-34.9, HR = 1.42 (1.18, 1.71) and BMI≥35, HR = 1.61 (1.21, 2.15) and with BMI≥35 (HR = 3.11 (1.72, 5.63)) for circulatory death. For US women, increased hazards were observed among BMI≥35 (HR = 2.10 (1.60, 2.76) for all-cause and circulatory HR = 3.04 (1.75, 5.30)). Swedish males with BMI≥35 had the highest absolute risk of premature death (762/100,000 person-years).

Conclusions: This study demonstrates a markedly increased risk of premature death associated with increasing BMI among Swedish males, a pattern not duplicated among females.

Keywords: Obesity; all-cause mortality; circulatory disease mortality; longitudinal studies; premature mortality.

Figure 1.

Hazard ratio gradient across BMI strata for (a) males and (b) females. Solid lines indicate hazard ratios for all-cause premature death; dotted lines indicate hazard ratios for premature circulatory death. Shaded labels indicate p < 0.05 relative to BMI = 18.5–24.9.

Figure 2.

Incidence density of premature death (per 100,000 person-years) across BMI strata for (a) male nonsmokers and (b) female nonsmokers. Solid lines depict all-cause premature death, and dotted lines depict premature circulatory death.