People who take exercise are biologically younger - by up to nine years - than those who don’t.

This striking finding may explain why exercise reduces the risk of heart attacks, diabetes, cancer, and other degenerative diseases. It actually suggests that active adults have cells that are measurably “younger” than those of inactive ones.

A team from King’s College London looked at biological molecules called telomeres that act as a clock, measuring the passage of the years. Telomeres are the caps at the end of the chromosomes, designed like the tips of a shoelace to protect them from damage.

In youth, telomeres are long, but they get shorter as we age, leading to a growing risk of damage. In the new study published in Archives of Internal Medicine the King’s team, together with colleagues from New Jersey, have shown that active people have longer telomeres than inactive ones.

They used data from the Twin Research Unit at King’s College to compare identical and non-identical twins, whose average age was just under 50. The study included more than 2,400 volunteers - mostly women - with an age range from 18 to 81.

Professor Tim Spector and Dr Lynn Cherkas from King’s, and Professor Abraham Aviv of New Jersey Medical School, asked the volunteers to fill in questionnaires about the amount of exercise they had done in the previous year. They also established whether they were smokers, their body mass index (BMI), and their socioeconomic status.

They found there was a significant link between telomere length in the volunteers’ white blood cells and the amount of exercise they took. This remained significant when adjusted for smoking, BMI, and social class.

Because genes also influence telomere length, the team checked the results by looking at a smaller group of identical twins. These pairs shared the same genes, but differed in their levels of everyday activity.

This confirmed that the link between telomere length and activity is also found in identical twins - powerful evidence that there is more to it than genetics.

The actual difference between active and inactive people was quite large. Dr Cherkas said: “Overall, the difference in telomere length between the most active subjects and the inactive subjects corresponds to around nine years of ageing.”

The team concludes: “The US guidelines recommend that 30 minutes of moderate-intensity physical activity at least five days a week can have significant health benefits.

“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.”

Professor Spector said: “Our study, performed on a large cohort, indicates that differences in telomere length between active and inactive individuals cannot be explained by variations in genes, smoking, BMI and socioeconomic status.

“A sedentary lifestyle appears to have an effect on telomere dynamics – thus providing a powerful message that could be used by clinicians to promote the potentially anti-aging effect of regular exercise.’

In a commentary in the same journal, Dr Jack Guralnik of the US National Institute on Ageing, says the results are provocative, but that more research is needed to prove them true.

“Persons who exercise are different from sedentary persons in many ways, and although certain variables were adjusted for in this analysis, many additional factors could be responsible for the biological differences between active and sedentary persons” he writes.

“Nevertheless, this article serves as one of many pieces of evidence that telomere length might be targeted in studying ageing outcomes.

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