By Rob Stein
Washington Post Staff Writer
Tuesday, January 29, 2008
Physically active people have cells that look younger on a molecular level than those of couch potatoes, according to new research that offers a fundamental new clue into how exercise may help stave off aging.
The study, involving more than 2,400 British twins, found for the first time that exercise appears to slow the shriveling of the protective tips on bundles of genes inside cells, perhaps keeping frailty at bay.
"These data suggest that the act of exercising may actually protect the body against the aging process," said Tim D. Spector, a professor of genetic epidemiology at King's College in London who led the study, published yesterday in the Archives of Internal Medicine.
Previous research has shown that being physically active reduces the risk of heart disease, cancer and other diseases, potentially extending longevity. In the hopes of helping explain how, Spector and his colleagues examined structures known as telomeres inside cells.
Telomeres cap the ends of chromosomes, the structures that carry genes. Every time a cell divides, the telomeres get shorter. When the telomeres get too short, the cell can no longer divide. Scientists believe that aging occurs as more and more cells reach the end of their telomeres and die -- muscles weaken, skin wrinkles, eyesight and hearing fade, organs fail, and thinking clouds.
Spector and his colleagues analyzed the telomeres from white blood cells collected from 2,401 twins participating in a long-term health study, examining whether there was a relationship between the subjects' telomere length and how much exercise they got in their spare time over a 10-year period.
"We're using telomere length as a marker of our rate of biological aging," Spector said.
The length of the twins' telomeres was directly related to their activity levels, the researchers found. People who did a moderate amount of exercise -- about 100 minutes a week of activity such as tennis, swimming or running -- had telomeres that on average looked like those of someone about five or six years younger than those who did the least -- about 16 minutes a week. Those who did the most -- doing about three hours a week of moderate to vigorous activity-- had telomeres that appeared to be about nine years younger than those who did the least.
"There was a gradient," Spector said. "As the amount of exercise increased, the telomere length increased."
Other researchers said the findings are intriguing.
"It's another jigsaw piece in trying to understand why exercise is important in longevity," said L. Stephen Coles, who studies aging at the University of California at Los Angeles. But Coles and others stressed that much more research is needed to definitively establish a causal relationship between exercise and aging.
"It's a fairly strong association and a very interesting association," said Jack M. Guralnik of the National Institute on Aging, who wrote an editorial accompanying the research. "But we have to interpret this with caution. People who choose to exercise are different in many ways from people who don't exercise. It's always difficult from these observational studies to determine whether it's the exercise that's having the effects."
Spector said the association held even after the researchers took into consideration factors that might explain the findings, such as the possibility that those who exercised least were more likely to smoke or to be obese or sick.
"We checked to make sure it wasn't due to obesity or smoking or marital status and everything else we could think of," Spector said. "We still found this marked effect."
The study did not address what happens to the telomeres of people who are sedentary for many years and later begin exercising.
When the researchers compared the least and most active twins with each other, they found about four years' difference in their telomeres, Spector said. "We wanted to see if we could account for the effect of genes," he said.
Spector said he hopes doctors can use the findings to encourage people to exercise.
"Hopefully when clinicians are advising patients, this could be another reason to offer," he said. "It may slow down the aging process, and people may actually look and feel younger, which we know would be a good thing for most of the population."