Importance of smoking habits for longitudinal and age-matched changes in body mass index: a cohort study of Swedish men and women

Background Previous longitudinal studies of smoking and BMI have focused on smoking cessation. The aim of the present study was to disentangle the effects of long-term smoking on longitudinal changes and age-matched BMI differences (time period effects) in a nation-wide Swedish cohort. Methods Men and women (n = 4349) ages 18–73 years reported height, weight, and smoking status for a baseline survey in 1980–1981. Eight and 16 years after baseline, follow-up surveys were conducted for 3244 (75%) of the 4349 subjects. Long-term smokers and long-term nonsmokers were compared with respect to longitudinal changes and age-matched BMI differences. Results For middle-age adults, the longitudinal increases in BMI were smaller among long-term smokers than long-term nonsmokers regardless of gender. Among the elderly, the longitudinal decrease in BMI was greatest among long-term smokers. Among men, age-matched BMI differences between surveys were smaller for long-term smokers than for nonsmokers. Among women, however, age-matched BMI differences were greater for long-term smokers than for nonsmokers. Conclusions In middle-age subjects, longitudinal BMI increases are smaller among smokers than nonsmokers. During old age, the BMI of smokers decreases more than that of nonsmokers. Unknown factors related to gender contribute to larger time period effects of smoking in women than in men.