The association between BMI value and long-term mortality.

OBJECTIVES: To study total mortality in different categories of BMI values, with adjustments for important covariates in a population-based 26-year mortality follow-up. Special interest will be given to gender differences and low BMI values.

METHODS: From a stratified sample in 1969 of 32 185 individuals aged 18-64 years from Stockholm County, 2422 underwent a health examination, with complete data obtained for 1020 subjects. BMI was classified as underweight (<20), normal (20-24.9), overweight (25-29.9) or obesity (> or =30). Participants were followed up in the National Cause of Death Register until the end of 1996. Multivariate analysis was performed by Cox regression for men and women separately, with different models, with step-wise adjustment for age, care need category, heart rate, hypertension, blood glucose, alcohol intake and smoking, with hazard ratios (HR) and 95% confidence interval (CI) and with normal weight as reference.

RESULTS: Among men, the age-adjusted HR was 1.68 (95% CI 1.10-2.57) for underweight and 1.62 (95% CI 1.08-2.43) for obesity, and among women it was 0.93 (95% CI 0.58-1.51) for underweight and 1.88 (95% CI 1.26-2.82) for obesity. In men, the significantly increased mortality remained when also adjusting for care need category, but not when adjusting for other factors, whereas the opposite was found regarding obesity. For women, underweight was significantly associated with decreased mortality when adjusting for smoking and for all factors together, whereas obesity was associated with increased mortality when adjusting for the different factors except for all factors together.

CONCLUSIONS: Underweight was associated with higher mortality among men, but not when adjusting for covariates, whereas underweight was associated with lower mortality among women when adjusting for smoking.