Smoking and obesity are both independent health risk factors but are also interrelated. Studies have demonstrated that smokers have a lower body mass index (BMI) than non-smokers that is not necessarily associated with a lower waist circumference. Moreover, smoking cessation has been associated with weight gain and an increase in waist circumference, but how this relationship affects mortality is unknown. This study sought to investigate the joint effects of smoking status and BMI and smoking status and waist circumference on all-cause mortality in a cohort of 149,502 men and 88,184 women aged 51-72 years from the National Institutes of Health-AARP Diet and Health Study. Smokers with a BMI <18.5 or ≥35 kg/m2 had a 6-8 times higher risk of all-cause mortality over the 10-year follow-up than non-smokers with a normal BMI. Moreover, smokers with a large waist circumference (fifth quintile) had a 5 times greater risk of all-cause mortality than non-smokers with a “normal” waist circumference (second quintile). Therefore, both smoking and adiposity (either overall or abdominal) are independent predictors of mortality, but the combination of smoking plus obesity or smoking plus abdominal obesity is related to an especially high mortality risk.
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