Background: Smoking and obesity are two of the most important risk factors for chronic disease today. Their combined effect on the risk of disability pension is not known.
Methods: A nationwide cohort of 45 920 Swedish men (18.7 + or - 0.5 years) were followed for 38 years. The body mass index (BMI), based on measured height and weight, was used to define underweight (<18.5), normal weight (18.5-24.9), overweight (25.0-29.9) and obesity (> or = 30.0). The hazard ratios (HRs) associated with BMI and smoking status at baseline for receiving disability pension were adjusted for socio-economic index (SEI), muscular strength, geographic region and place of residence.
Results: During 1.6 million person-years, 4631 disability pensions and 2897 deaths occurred. After adjustment, overweight (HR 1.34, 95% CI 1.19-1.51) and obesity (HR 1.55, 1.18-2.05) were associated with an increased risk of disability pension, independent of smoking, whereas underweight (18.5; HR 1.07, 0.97-1.17) was not compared with normal weight. Similarly, smoking 1-10 (HR 1.37, 1.27-1.49) or >10 cigarettes per day (HR 2.01, 1.86-2.17) showed independent risk increases versus non-smoking. Although obese individuals smoking >10 daily cigarettes were at greatly increased risk (HR 2.98, 1.98-4.47), no evidence of interaction between the two risk factors could be detected.
Conclusions: Both increased adiposity and smoking are strong and independent predictors of disability pension, but they do not act synergistically.