Body mass index and risk of cardiovascular disease, cancer and all-cause mortality

Objectives: To determine the dose-response relationship between body mass index (BMI) and cause-specific mortality among Canadian adults. Methods: The sample includes 10,522 adults 18-74 years of age who participated in the Canadian Heart Health Surveys (1986-1995). Participants were divided into 5 BMI categories (<18.5, 18.5-24.9, 25-29.9, 30-34.9, and ≥35 kg/m²). Multivariate-adjusted (age, sex, exam year, smoking status, alcohol consumption and education) hazard ratios for all-cause, cardiovascular disease (CVD) and cancer mortality were estimated using Cox proportional hazards regression. Results: There were 1,149 deaths (402 CVD; 412 cancer) over an average of 13.9 years (range 0.5 to 19.1 years), and the analyses are based on 145,865 person-years. The hazard ratios (95% CI) across successive BMI categories for all-cause mortality were 1.25 (0.83-1.90), 1.00 (reference), 1.06 (0.92-1.22), 1.27 (1.07-1.51) and 1.65 (1.29-2.10). The corresponding hazard ratios for CVD mortality were 1.30 (0.60-2.83), 1.00 (reference), 1.57 (1.22-2.01), 1.72 (1.27-2.33) and 2.09 (1.35-3.22); and for cancer, the hazard ratios were 1.02 (0.48-2.21), 1.00 (reference), 1.14 (0.90-1.44), 1.34 (1.01-1.78) and 1.82 (1.22-2.71). There were significant linear trends across BMI categories for all-cause (p=0.0001), CVD (p<0.0001) and cancer mortality (p=0.003). Conclusions: The results demonstrate significant relationships between BMI and mortality from all causes, CVD and cancer. The increased risk of all-cause, CVD and cancer mortality associated with an elevated BMI was significant at levels above 30 kg/m²; however, overweight individuals (BMI 25-29.9 kg/m²) also had an approximately 60% higher risk of CVD mortality.