Reducing sedentary time protects DNA

Less time spent sitting may lengthen telomeres and protect DNA from age-related damage, a new study shows. However, the researchers found no significant association in telomere length with increased exercise in this small randomized trial.

"We're excited about this study," said lead author Mai-Lis Hellenius, MD, PhD, a professor of cardiovascular disease prevention in the Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden. "Long telomeres are linked to a longer, healthier life."

Per Sjögren, PhD, from the Unit of Clinical Nutrition and Metabolism, Department of Public Health and Caring Sciences, Uppsala University, Sweden, and colleagues published the study online September 3 in the British Journal of Sports Medicine.

Telomeres are sections of DNA that protect the ends of chromosomes from damage during cell division. Telomeres tend to shorten with age, and previous research has linked shorter telomeres with shorter life spans and increased risk for some types of cancer and cardiovascular disease.

"Our DNA will be damaged during a lifetime," Dr. Hellenius said. "It's damaged by bad diets, smoking, infections, and so on. Our capability to copy and produce new DNA and new cells is so important."

Previous research has shown that people who exercise more tend to have longer telomeres.

In the current study, Dr. Sjögren and colleagues analyzed the length of telomeres a subset of people who had participated in a randomized exercise trial. The original study included 101 predominantly sedentary and overweight people adults aged 68 years at baseline. The investigators randomly assigned half of the participants to an exercise program and the other half to their regular behavior.

They asked the participants to keep a 7-day diary and to wear a pedometer to measure the number of steps taken every day. They also asked them to fill out a questionnaire tallying up the amount of time spent sitting down each day.

As the researchers reported previously, the time spent exercising, as well as the number of steps taken daily, increased significantly in the group assigned the exercise program, whereas the amount of time spent seated fell in both groups ( Br J Sports Med. 2011;45:158). Various risk factors for heart disease and stroke also improved in both groups, particularly those on the exercise program, who lost more weight than their counterparts left to their own devices.

In the current subset analysis, the researchers examined telomere length from blood samples drawn at baseline and after the 6-month intervention in 49 randomly chosen participants. They found that the number of daily steps taken was not associated with changes in telomere length.

An increase in moderate-intensity physical activity correlated to a shortening in telomere length in both groups, but this finding was not statistically significant. However, a reduction in the amount of time spent sitting in the exercise group was associated with telomere lengthening in blood cells.

"We hypothesise that a reduction in sitting hours is of greater importance than an increase in exercise time for elderly risk individuals," the researchers conclude.

Dr. Hellenius acknowledged that the study was a small one and needed to be replicated before drawing conclusions from it. However, she notes, other research has also shown that people who spend more time sitting have shorter lives, regardless of whether they also exercise regularly.

"So I think you can say to our patients yes, it's important to break up sedentary time and take a break for 1 or 2 minutes every 30 minutes," said Dr. Hellenius.