Background and objective: Physical activity level and obesity are both partly determined by genes and childhood environment. To determine the associations between long-term leisure-time physical activity, weight gain and waist circumference and whether these are independent of genes and childhood effects.
Design and subjects: The study design is a 30-year follow-up twin study in Finland. For this study, 146 twin pairs were comprehensively identified from the large Finnish Twin Cohort. These twin pairs were discordant for both intensity and volume of leisure physical activity in 1975 and 1981 and were healthy in 1981. At follow-up in 2005, both members of 89 pairs were alive and participated in a structured telephone interview. In the interview self-measured weight and waist circumference, and physical activity level for the whole follow-up were assessed. Paired tests were used in the statistical analyses.
Main outcome measures: Waist circumference at 30-year follow-up (2005) and change in weight from 1975 to 2005.
Results: In the 42 twin pairs discordant for physical activity at all time points during the 30-year period, the mean weight gain from 1975 through 2005 was 5.4 kg (95% confidence interval (CI) 2.0-8.9) less in the active compared to inactive co-twins (paired t-test, P=0.003). In 2005, the mean waist circumference was 8.4 cm (95% CI 4.0-12.7) less in the active compared with inactive co-twins (P<0.001). These trends were similar for both monozygotic and dizygotic twin pairs. Pairwise differences in weight gain and waist circumference were not seen in the 47 twin pairs, who were not consistently discordant for physical activity.
Conclusion: Persistent participation in leisure-time physical activity is associated with decreased rate of weight gain and with a smaller waist circumference to a clinically significant extent even after partially controlling for genetic liability and childhood environment.