The fact that exercising too little and eating too much can lead to weight problems and in turn reduce one's life expectancy is (or should be) common knowledge. However, there could be a more direct link between exercise and lifespan, according to a new study quoted by the New Scientist.
The study, which was carried out by Tim Spector and his team at St Thomas' hospital in London, suggests that exercising too little can reduce a person's life expectancy even if that person isn't overweight and doesn't smoke:
Telomeres shorten each time a cell divides, and when they become too short a cell can no longer divide, so telomeres act as a kind of timer counting down our biological age. . . . The researchers found that people who did not exercise in their spare time had shorter telomeres than very active people. . . . On average, the least active (getting just 16 minutes exercise a week) had telomeres 200 base pairs shorter than the most active (exercising 3 hours a week), which translates to them being about 10 years biologically older.
The team previously showed that smoking and obesity can shorten telomere length to the equivalent of 10 years. But they found that exercise and telomere length were linked independently of whether people smoked or were overweight. . . . Accounting for whether or not participants had a chronic disease (possibly making them sedentary) did not change the findings either, suggesting that other factors linked with an inactive lifestyle affect biological age.
The researchers speculate that the telomere-reducing factor in inactive but otherwise healthy people may be psychological stress, which "could translate into oxidative stress, a source of free radicals that can cause DNA mutations and shorten telomere length." That link would explain why exercise carried out during one's free time seems to help with cellular ageing, while paradoxically, exercise stemming from manual labor shortens telomere length.