Long-term physical activity has an anti-aging effect at the cellular level (USA)

"Intensive exercise prevented shortening of telomeres, a protective effect against aging of the cardiovascular system, according to research reported in Circulation: Journal of the American Heart Association. Researchers measured the length of telomeres - the DNA that bookends the chromosomes and protects the ends from damage - in blood samples from two groups of professional athletes and two groups who were healthy nonsmokers, but not regular exercisers. The telomere shortening mechanism limits cells to a fixed number of divisions and can be regarded as a "biological clock." Gradual shortening of telomeres through cell divisions leads to aging on the cellular level and may limit lifetimes. When the telomeres become critically short the cell undergoes death. The 2009 Nobel Prize in Physiology or Medicine was awarded to researchers who discovered the nature of telomeres and how chromosomes are protected by telomeres and the enzyme telomerase."