Obesity but not overweight is associated with increased mortality risk

The association between body mass index (BMI) and survival has been described in various populations. However, the results remain controversial and information from low-prevalence Western countries is sparse. Our aim was to examine this association and its public health impact in Switzerland, a country with internationally low mortality rate and obesity prevalence. We included 9,853 men and women aged 25–74 years who participated in the Swiss MONICA (MONItoring of trends and determinants in CArdiovscular disease) study (1983–1992) and could be followed up for survival until 2008 by using anonymous record linkage. Cox regression models were used to calculate mortality hazard ratios (HRs) and to estimate excess deaths. Independent variables were age, sex, survey wave, diet, physical activity, smoking, educational class. After adjustment for age and sex the association between BMI and all-cause mortality was J shaped (non-smokers) or U shaped (smokers). Compared to BMI 18.5–24.9, among those with BMI ≥ 30 (obesity) HR for all-cause mortality was 1.41 (95% confidence interval: 1.23–1.62), for cardiovascular disease (CVD) 2.05 (1.60–2.62), for cancer 1.29 (1.04–1.60). Further adjustment attenuated the obesity-mortality relationship but the associations remained statistically significant. No significant increase was found for overweight (BMI 25–29.9). Between 4 and 6.5% of all deaths, 8.8–13.7% of CVD deaths and 2.4–3.9% of cancer deaths could be attributed to obesity. Obesity, but not overweight was associated with excess mortality, mainly because of an increased risk of death from CVD and cancer. Public health interventions should focus on preventing normal- and overweight persons from becoming obese.