There is an old saying: "the more time you waste, the more you have." According to a new study, the biological truth is precisely the opposite. Physically active people are not just healthier, they are actually biologically younger than those with sedentary lifestyles. Furthermore, those who get regular exercise have lower rates of age-related, life-shortening conditions such as cardiovascular disease, type 2 diabetes, cancer, high blood pressure, obesity and osteoporosis.

"A sedentary lifestyle increases the propensity to aging-related disease and premature death," the study authors write. "Inactivity may diminish life expectancy not only by predisposing to aging-related diseases but also because it may influence the aging process itself."

Lynn F. Cherkas, Ph.D., of King's College London, and colleagues studied 2,401 white twins, looking at physical activity level, smoking habits and socioeconomic status. Subjects also provided a blood sample for DNA testing. The researchers measured the length of what are called telomeres, (repeated sequences at the end of chromosomes), in the twins' white blood cells. These telomeres shorten over time and are thought to be a marker of biological age.

In the study, published in the January 28 issue of Archives of Internal Medicine, men and women who were less physically active were found to have shorter white blood cell telomeres.

"The U.S. guidelines recommend that 30 minutes of moderate-intensity physical activity at least five days a week can have significant health benefits," the authors write. "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." Take a look at TheDoctor's series, Feel Younger, for information on starting an exercise program.