Smoking and BMI change association across adulthood: pooled analysis of 13 longitudinal twin cohorts

Abstract Background Smoking is linked to lower body weight, and concerns about weigh gain may decrease motivation to smoking cessation. Since the long-term impact of smoking on BMI changes is still unclear, we examined how smoking status relates to BMI changes at different life stages. Data and methods Data pooled from 13 longitudinal twin cohorts comprising 91,357 individual twins (45% females) were used. BMI changes were estimated using the delta method if only two measures were available or linear mixed-effects (LME) models if three or more measures were available. Smoking status was categorized as never smokers, current smokers, and former smokers. We first assessed the overall associations between smoking status and BMI changes and then examined these associations in different life stages. Results Over the total life course, BMI changes were smaller in current smokers than in never smokers in men (β = -4.70e-03 kg/m2 per year). When considering different life stages, in men, former smokers had greater BMI changes in late middle age and old age compared to never smokers (β = 6.12e-03 kg/m2 per year and β = 5.48e-03 kg/m2 per year, respectively) and current smokers (β = 0.01 kg/m2 per year and β = 0.02 kg/m2 per year, respectively). In women, current smokers had lower BMI changes in late middle age and old age compared to never smokers (β = -0.01 kg/m2 per year in late middle age and β = -0.02 kg/m2 per year in old age) and former smokers (β = 0.02 kg/m2 per year in both stages). Conclusions The associations between smoking status and BMI change can vary depending on life stage and sex. Former smokers tend to gain more weight, particularly in later life, underscoring the importance of targeted interventions following smoking cessation. Key messages • Over the total life course, only currentsmokers showed lower BMI changes compared to never smokers. • When considering different life stages, the number of associations increase, conveying that the associations between smoking status and BMI change can vary depending on life stage and sex.