Associations of sitting time with leisure-time physical inactivity, education, and body mass index change.

We aimed to investigate the associations of long-term leisure-time physical inactivity, body mass index (BMI) change, and education with sitting time in a 35-year follow-up based on self-reports in surveys. Influences of working status in 2011 and familial confounding on the associations were tested. Data were based on the population-based Finnish Twin Cohort of 5232 twins (53-67-year-old, 41% men) with four surveys in 1975-2011. Statistical analyses were performed using linear regression with several covariates. The effect of familial confounding (genetics and shared environment) was analyzed using a co-twin control design which should be interpreted as if familial confounding plays a role, an association should be seen among all individuals but not in discordant twin pairs. Compared to those not at work, those at work had a longer total sitting time/d. For those at work, higher education was associated with more total sitting but with less non-work sitting. Long-term leisure-time physical inactivity was associated with more non-work sitting among those at work, whereas long-term weight gain with more total and non-work sitting regardless of working status. Familial confounding attenuated the associations, except for the association of increasing BMI with total and non-work sitting among women at work. To conclude, total sitting time was longer among those still at work, but it was also influenced by long-term leisure-time physical inactivity, higher education, and an increase of BMI over the years. Public health efforts should be targeted to reduce sedentary behavior by promoting life-long leisure-time physical activity and weight control.