The mortality risk of smoking and obesity combined

Both smoking and obesity have been linked to increased mortality, but evaluating the joint effect has been limited. This nationwide, prospective mortality study of U.S. radiologic technologists was designed to evaluate the combined mortality risks of obesity and smoking.

Mortality risk was investigated in 64,120 women and 18,760 men who completed a baseline questionnaire (1983 to 1989). Body mass index (BMI) (weight adjusted for height, or kilograms divided by meters squared) was calculated from self-reported weight and height at baseline, with five categories: less than 18.5 (underweight), 18.5 to 24.9 (normal), 25.0 to 29.9 (overweight), 30.0 to 34.9 (moderately obese), and 35.0 and higher (very obese). Participants were followed from the questionnaire until the date of death or through 2002, whichever occurred first. The combined association among BMI and smoking and all-cause, cancer, and circulatory disease mortality by gender and attained age (less than 65 years, 65 years and older) was examined using Cox proportional hazards regression analyses (conducted in 2005). Person-years at risk averaged 16 years (women aged less than 65), 6 years (women aged 65 and older), 15 years (men aged less than 65), and 7 years (men aged 65 and older), totaling 1.35 million person-years.

In all gender/age groups, both obesity and smoking, particularly current smoking, contributed substantially to all-cause mortality, with 3.5- to 5-fold risks for very obese, current smokers compared to normal weight, never smokers. Current smoking was the predominant risk factor for cancer mortality. Combining obesity with current smoking increased circulatory disease mortality by 6- to 11-fold for people aged less than 65 years, compared to normal weight, never smokers. Obese former smokers (less than 65 years) had notably lower risks.

Obese smokers (aged less than 65 years) had strikingly high mortality risks, particularly from circulatory disease mortality.