Associations of Smoking Status and Leisure-time Physical Activity with Waist Circumference Change Ten-year Follow-up among Twin Adults

BACKGROUNDThis cohort study investigated the associations of smoking status and leisure-time physical activity (LTPA) with weight circumference (WC) change. METHODSIn the FinnTwin16 cohort, 3,322 twins (46% men) reported smoking status, LTPA, and WC in early adulthood and 10 years later providing information on essential covariates at baseline. The effects of smoking and LTPA (metabolic equivalent tasks [MET]-h/week) on WC change (cm) were estimated by modelling WC value at the end of follow-up and adjusted for baseline WC in linear regression models. Within-pair associations were analyzed using linear fixed-effect regressions among 660 dizygotic and 390 monozygotic twin pairs. RESULTSDuring the 10-year follow-up, 36.4% (n=273) of baseline daily smokers quit smoking. Among those who quit daily smoking, the mean WC increase was 8.4 cm (SD 8.1). Quitters who smoked daily at baseline increased WC by about 2 cm more than continuing smokers (adjusted {beta} 2.04; 95% CI 0.94, 3.14). This association was not robust after shared familial influences were controlled for. In general, the participants decreased LTPA during follow-up, except the quitters with the mean LTPA increase of 5.0 MET-h/week (SD 35.0). Independently of smoking status, each additional MET-h/week was associated with 0.06 cm less WC increase (adjusted {beta} -0.06; 95% CI - 0.07, -0.05). This association was replicated in the within-pair analyses. CONCLUSIONSSmoking cessation seems to be associated with WC increase, but familial confounding may be involved in this process. LTPA appears to mitigate increases in WC independently of smoking status and familial influences.