People who are physically active may be biologically younger than sedentary people the same age. VOA's Carol Pearson reports on a new study that finds regular exercise may be key in slowing the aging process. Studies show staying fit cuts the risk of heart disease, diabetes and cancer. Now scientists say the benefits of regular exercise show up in individual cells. Professor Elissa Epel specializes in stress and cellular aging. She explains, "Looking into our cells is actually a window into how our bodies are aging. So our cell aging is linked to how quickly we get disease and to how long we live. "In the study, British researchers took blood samples from 2,400 twins. They studied their DNA -- specifically the telomeres, protective caps on the end of chromosomes that prevent DNA damage. Telomeres get shorter as we age so the longer these strands are, the younger our cells are. The researchers found that the telomeres of people who exercised about 30 minutes a day were significantly longer than those of sedentary people who were the same chronological age. The findings do not surprise Professor Epel, who says, "This is the first study that's shown a factor that actually prevents or slows cell aging. So it's very exciting. "People in the study who spent an average of 30 minutes a day exercising had cells that appeared up to 10 years younger than those who did not exercise. The researchers suspect that exercise helps reduce the inflammation and stress that damage our cells and shorten our lives.