Background Telomere length has been associated with a healthy lifestyle and longevity. However, the effect of increased physical activity on telomere length is still unknown. Therefore, the aim was to study the relationship between changes in physical activity level and sedentary behaviour and changes in telomere length.

Methods Telomere length was measured in blood cells 6 months apart in 49, 68-year-old, sedentary, overweight individuals taking part in a randomised controlled physical activity intervention trial. The intervention group received individualised physical activity on prescription. Physical activity was measured with a 7-day diary, questionnaires and a pedometer. Sitting time was measured with the short version of The International Physical Activity Questionnaire.

Results Time spent exercising as well as steps per day increased significantly in the intervention group. Reported sitting time decreased in both groups. No significant associations between changes in steps per day and changes in telomere length were noted. In the intervention group, there was a negative correlation between changes in time spent exercising and changes in telomere length (rho=−0.39, p=0.07). On the other hand, in the intervention group, telomere lengthening was significantly associated with reduced sitting time (rho=−0.68, p=0.02).

Conclusions Reduced sitting time was associated with telomere lengthening in blood cells in sedentary, overweight 68-year-old individuals participating in a 6-month physical activity intervention trial.