Background: Prospective studies of overweight and coronary heart disease (CHD) have presented inconsistent findings. Previous inconsistencies may be explained by the modifying effect of cigarette smoking on the association between weight gain and coronary mortality.
Methods and results: We prospectively studied 1531 men 40 to 59 years of age who were employed at the Hawthorne Works of the Western Electric Company in Chicago, Ill. Information collected at the initial examination in 1958 included recalled weight at age 20, present weight, height, smoking status, and other CHD risk factors. Vital status was known for all men on the 25th anniversary: 257 CHD deaths occurred over 31,644 person-years of experience. Cox regression analysis was used to investigate risk of coronary mortality associated with change in body mass index (deltaBMI) and its modification by smoking status after adjustment for age, major organ system disease, family history of CHD, and BMI at age 20. Adjustment was not performed for blood pressure or serum total cholesterol because these are intervening variables. DeltaBMI was positively associated with risk of coronary mortality in never-smokers but not in current-smokers (P for interaction =.088). For never-smokers with deltaBMI classified as stable, low gain, moderate gain, or high gain, adjusted relative risks of coronary mortality were 1.00, 1.75, 1.75, and 3.07, respectively (P for trend=.010). For current-smokers, the respective adjusted relative risks were 1.00, 0.78, 1.05, and 1.03 (P for trend=.344).
Conclusions: These results support the hypothesis that cigarette smoking modifies the association between weight gain and coronary mortality. Future investigations of weight gain and coronary mortality should account for the modifying effect of cigarette smoking.