Obesity and loss of disease-free years owing to major non-communicable diseases: a multicohort study

Background Obesity increases risk of several chronic diseases, but the extent to which the obesity-related loss of disease-free years vary by lifestyle category and across the social hierarchy is unclear. We estimated the number of years free from major chronic diseases by body mass index (BMI) category between the ages 40 and 75 years. Methods We pooled individual-level data on BMI and major non-communicable diseases from 120,181 men and women initially without evidence of these diseases in ten European cohort studies (the IPD-Work Consortium). BMI was assessed at baseline in 1991-2008 and noncommunicable diseases (incident type-2 diabetes, coronary heart disease, stroke, cancer, asthma and chronic obstructive pulmonary disease) were ascertained via linkage to records from national health registries, repeated medical examinations, or selfreport. Disease-free years associated with underweight (BMI<18·5 kg/m2), overweight (BMI=25-29·9 kg/m2) and obesity (BMI=30-34.9 kg/m2, class-I [mild], BMI≥35 kg/m2, class-II-III [severe]) compared to normal weight (BMI=18·5-24·9 kg/m2) were estimated from age 40 to 75 years. Findings Of the 47 127 men, 0·4% were underweight, 45·6% normal weight, 44·0% overweight, 8·4% class I obese (mild obesity), and 1·5% class II-III obese (severe obesity). The corresponding proportions among the 73 054 women were 2·0%, 61·3%, 26·8%, 7·8% and 2·2%, respectively. During 1,328,873 person-years at risk (mean follow-up 11·5 years), 8159 men and 8100 women developed one or more noncommunicable disease. Between the ages of 40 and 75 years, the estimated number of disease-free life-years was 29·3 in normal-weight men and 29·4 in normal-weight women. In men, compared to normal weight, the loss of disease-free years was 1·8 (95% confidence interval -1·3–4·9) in underweight, 1·1 (0·7–1·5) for overweight, 3·9 (2·9–4·9) for class-I obese and 8·5 (7·1–9·8) years for class II-III obese. The corresponding estimates for 3 women were 0·0 (-1·4–1·4) for underweight, 1·1 (0·6–1·5) for overweight, 2·7 (1·5–3·9) for class-I obese and 7·3 (6·1–8·6) for class-II-III obese. The loss of disease-free years associated with class-II-III obesity varied between 7.1 and 10.0 years in subgroups of participants with different socioeconomic groups, physical activity levels and smoking habits. Interpretation On average, mild obesity is associated with a loss of one-tenth and severe obesity a loss of one-fourth of potential disease-free years during middle and later adulthood. This increasing loss of disease-free years as obesity becomes more severe is seen in both sexes, among smokers and non-smokers, the physically active and inactive, and across the social hierarchy.