If you need proof that exercise helps to keep you young, look at the exciting study from King's College in London, England reported in the Archives of Internal Medicine (January 28, 2008). The researchers showed that people who exercise regularly have telomeres in the DNA of their white blood cells that are longer than those of couch potatoes. White blood cell telomeres shorten over time and serve as a marker of a person's biological age.
The active ends of genetic material in cells are covered with a layer of proteins called telomeres. If they weren't, the exposed ends of the genetic material would stick to anything nearby and the cells would die. However, each time a cell divides to make two cells, a little bit of the telomere is removed. Eventually the telomere is gone, the ends of genetic material stick together and the cell can no longer divide so it dies without replacing itself. Obviously, the longer the telomeres, the longer it will take for the telomeres to be used up so the cells are viable longer.
The study compared physical activity, smoking and socioeconomic status in 2,401 sets of twins. Those who were more active had longer leukocyte telomeres than those who were less active. The researchers concluded that "The mean difference in leukocyte telomere length between the most active (who performed an average of 199 minutes of physical activity per week) and the 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 10 years younger, on average."