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(HealthDay News) -- People who are physically active in their free time may be biologically younger than couch potatoes, a new British study suggests.

"A sedentary lifestyle increases the propensity to aging-related diseases and premature death. Inactivity may diminish life expectancy not only by predisposing to aging-related diseases, but also because it may influence the aging process itself," study author Lynn F. Cherkas, of King's College London, said in a prepared statement.
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The researchers looked at the physical activity levels, smoking habits and socioeconomic status of 2,401 white twins. The researchers also collected DNA samples from participants, and examined the length of telomeres-repeated sequences at the end of chromosomes in white blood cells (leukocytes). Leukocyte telomeres shorten over time and may serve as a marker of a person's biological age.

Overall, the study participants had an average telomere loss of 21 nucleotides (structural units) per year. But those who were more active in their leisure time had longer leukocyte telomeres than those who were less active.

"Such a relationship between leukocyte telomere length and physical activity remained significant after adjustment for body-mass index, smoking, socioeconomic status and physical activity at work," the authors wrote.

"The mean difference in leukocyte telomere length between the most active [who performed an average of 199 minutes of physical activity per week] and least active [16 minutes of physical activity per week] subjects was 200 nucleotides, which means that the most active subjects had telomeres the same length as sedentary individuals up to 10 years younger, on average."

Oxidative stress damage caused to cells by exposure to oxygen and inflammation may be a factor contributing to shorter telomere length in sedentary people. Stress has also been linked to telomere length. Exercise may reduce stress and its effect on telomeres and the aging process, the study authors suggested.

"The U.S. guidelines recommend that 30 minutes of moderate-intensity physical activity at least five days a week can have significant health benefits," they wrote. "Our results underscore the vital importance of these guidelines. They show that adults who partake in regular physical activity are biologically younger than sedentary individuals. This conclusion provides a powerful message that could be used by clinicians to promote the potential anti-aging effect of regular exercise."

But more research is needed to confirm a direct link between physical activity and aging, the study added.

"Persons who exercise are different from sedentary persons in many ways, and although certain variables were adjusted for in this analysis, many additional factors could be responsible for the biological differences between active and sedentary persons, a situation referred to by epidemiologists as residual confounding," Dr. Jack M. Guralnik, of the U.S. National Institute on Aging, wrote in an accompanying editorial.

"Nevertheless, this article serves as one of many pieces of evidence that telomere length might be targeted in studying aging outcomes," he added.

The study was published in the Jan. 28 issue of the Archives of Internal Medicine.