Long-term physical activity has an anti-ageing effect at the cellular level, a German study suggests.
Researchers focused on telomeres, the protective caps on the chromosomes that keep a cell's DNA stable but shorten with age.
They found telomeres shortened less quickly in key immune cells of athletes with a long history of endurance training.
The study, by Saarland University, appears in the journal Circulation.
This is direct evidence of an anti-ageing effect of physical exercise
Dr Ulrich Laufs
In a separate study of young Swedish men, cardiovascular fitness has been linked to increased intelligence and higher educational achievement.
Telomeres are relatively short sections of specialised DNA that sit at the ends of all our chromosomes.
They have been compared to the plastic tips at the ends of shoelaces that prevent the laces from unravelling.
Each time a cell divides, its telomeres shorten and the cell becomes more susceptible to dying.
The researchers measured the length of telomeres in blood samples from two groups of professional athletes and two groups of people who were healthy non-smokers, but who did not take regular exercise.
One group of professional athletes included members of the German national track and field athletics team, who had an average age of 20.
The second group was made up of middle-aged athletes who had regularly run long distances - an average of 80km a week - since their youth.
The researchers found evidence that the physical exercise of the professional athletes led to activation of an enzyme called telomerase, which helped to stabilise telomeres.
This reduced the telomere shortening in leukocytes, a type of white blood cell that plays a key role in fighting infection and disease.
The most pronounced effect was found in athletes who had been regularly endurance training for several decades.
Potency of training
Lead researcher Dr Ulrich Laufs said: "This is direct evidence of an anti-ageing effect of physical exercise.
"Our data improves the molecular understanding of the protective effects of exercise and underlines the potency of physical training in reducing the impact of age-related disease."
It is still difficult to separate cause and effect from these studies - as longer telomeres may still be a marker of fitness
Professor Tim Spector
Kings College London
Professor Tim Spector, an expert on genetics and ageing at Kings College London, said other studies had suggested more moderate exercise had a beneficial effect on ageing.
He said: "It is still difficult to separate cause and effect from these studies - as longer telomeres may still be a marker of fitness.
"Nevertheless - this is further evidence that regular exercise may retard aging."
Professor Kay-Tee Khaw, of the University of Cambridge, an expert on ageing, said: "The benefits of physical activity for health are well established from many large long-term population studies.
"Even moderate levels of physical activity are related to lower levels of many heart disease risk factors such as blood pressure and cholesterol and lower risk of many chronic diseases associated with ageing such as heart disease, stroke, diabetes and some cancers."
In the second study, published in Proceeding of the National Academy of Sciences, a team from the University of Gothenburg analysed data on more than 1.2 million Swedish men born from 1950-1976 who enlisted for military service at age 18.
They found that good heart health was linked to higher intelligence, better educational achievement and raised status in society.
By studying twins in the study, the researchers concluded that environmental and lifestyle factors were key, rather than genetics.
They said the findings suggested that campaigns to promote physical exercise might help to raise standards of educational achievement across the population.
Lead researcher Professor Georg Kuhn said cardiovascular exercise increased blood flow to the brain, which in turn might help forge more and stronger connections between nerve cells.
However, he said it was also possible that intelligent people tended to make more exercise.