U-shaped association of body mass index in early adulthood with unintentional mortality from injuries: a cohort study of Swedish men with 35 years of follow-up

OBJECTIVES: To investigate the dose-response association between body mass index (BMI) in young adulthood and the risk of mortality caused by unintentional injuries. METHODS: We performed a cohort study including 7 43 398 men identified by linkage of the Multigeneration Register and the Military Service Conscription Register. Cox regression models were used to examine crude and adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) of the relationships between BMI at age 18-20 years and the risk of death from all unintentional injuries as well as from specific unintentional injuries. We then estimated the population attributable fractions (PAFs)-the proportion of unintentional deaths that was attributable to underweight, overweight and obesity in this population-based cohort. RESULTS: During 35.9 years of follow-up, 6461 deaths occurred from unintentional injuries, including 3064 deaths from road injury, 978 from poisoning, 503 from falls, 243 from fire and 348 from drowning. Underweight subjects had a higher risk of mortality in all unintentional injuries (HR, 1.05; 95% CI, 1.03-1.10) and mortality in burns (HR, 1.65; 95% CI, 1.13-2.40) compared with BMI between 18.5 and 22.5 kg m(-2) (reference group). BMI>25 kg m(-2) was associated with increased risk of death from all unintentional injuries (HR, 1.36; 95% CI, 1.12-1.65) and road accidents (HR, 1.50; 95% CI, 1.14-1.97). Estimates of PAF suggested that 4.4% of the mortality in Swedish men caused by unintentional injuries could have been avoided if BMI values were kept between 18.5 and 22.5 kg m(-2). CONCLUSIONS: A U-shaped association was observed between BMI and risk of unintentional death. Both underweight and overweight were associated with increased mortality risk for all unintentional injuries and for subtype causes. Our study suggests that BMI might be a significant target for preventive interventions on deaths caused by unintentional injuries.