The more exercise people get, the less their cells appear to age. In a new study in Preventive Medicine, people who exercised the most had biological aging markers that appeared nine years younger than those who were sedentary.

Researchers looked at the telomeres from nearly 6,000 adults enrolled in a multi-year survey run by the Centers for Disease Control and Prevention. People were asked what physical activities they had done in the past month and how vigorously they did them. They also provided DNA samples, from which the researchers measured telomere length. Telomeres, the protein caps on the ends of human chromosomes, are markers of aging and overall health. Every time a cell replicates, a tiny bit of telomere is lost, so they get shorter with age. But they shrink faster in some people than in others, explains study author Larry Tucker, professor of exercise science at Brigham Young University.

“We know that, in general, people with shorter telomeres die sooner and are more likely to develop many of our chronic diseases,” says Tucker. “It’s not perfect, but it’s a very good index of biological aging.”

After adjusting for smoking, obesity, alcohol use, gender, race and other factors, Tucker found in his study that people who exercised the most had significantly longer telomeres than those who were sedentary. The most sedentary people had 140 fewer base pairs of DNA at the ends of their telomeres, compared to the most active: a difference of about nine years of cellular aging, he says.

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