A hormone released into the blood by muscles after bouts of exercise may provide an indicator of biological age, say scientists.

Irisin is known to reprogramme fat cells so that they burn energy instead of storing it, thereby contributing to the slimming effect of exercise.

The new research shows that higher blood levels of irisin are associated with telomere length, a genetic marker of youthfulness.

Telomeres are protective caps on the ends of chromosomes that shorten as cells replicate.

Short telomere length has been linked to age-related health problems including cancer, heart disease and Alzheimer’s.

Scientists found that people with higher amounts of irisin also had longer telomeres, helping to explain the rejuvenating effect of keeping active.

Lead researcher James Brown, from the Centre for Healthy Ageing at Aston University, Birmingham, said: “Exercise is known to have wide-ranging benefits, from cardiovascular protection to weight loss.

“Recent research has suggested that exercise can protect people from both physical and mental decline with ageing. Our latest findings now provide a potential molecular link between keeping active and a healthy ageing process.”

The study, published in the journal Age, involved 81 healthy participants aged 18 to 83 recruited locally in Birmingham.

The researchers wrote: “In summary, we report that plasma irisin can predict relative TL (telomere length) in healthy individuals. However, the precise mechanism through which irisin exerts its potentially anti-ageing effects warrant further investigation.”