Taking more exercise and eating the right foods may help increase levels of an enzyme vital for guarding against age-related cell damage, work suggests.

Among 24 men asked to adopt healthy lifestyle changes for a US study in The Lancet Oncology, levels of telomerase increased by 29% on average.

Telomerase repairs and lengthens telomeres, which cap and protect the ends of chromosomes housing DNA.

As people age, telomeres shorten and cells become more susceptible to dying.

It is the damage and death of cells that causes aging and disease in people.

Several factors such as smoking, obesity and a sedentary lifestyle are associated with shorter-than-average telomeres.

Professor Dean Ornish, from the Preventive Medicine Research Institute in California, and his team wanted to find out if improvements in diet and lifestyle might have the opposite effect.

They asked 30 men, all with low-risk prostate cancers, to take part in a three-month trial of comprehensive lifestyle changes.

These consisted of a diet high in fruit and vegetables, supplements of vitamins and fish oils, an exercise regimen and classes in stress management, relaxation techniques and breathing exercises.

Telomerase activity was measured at the beginning of the trial and again at the end.

Among the 24 men who had sufficient data for analysis, blood levels of telomerase increased by 29% on average.

Increases in telomerase activity were linked with decreases in "bad" LDL cholesterol and decreases in one measure of stress - intrusive thoughts.

The researchers say it is too early to tell if the boost in telomerase levels will translate to a change in telomere length.

But there is evidence to suggest that telomere shortness and low telomerase activity might be important risk factors for cancer and cardiovascular disease.

"This might be a powerful motivator for many people to beneficially change their diet and lifestyle," they told The Lancet Oncology.

Professor Tim Spector, from King's College London, who has been researching aging and telomeres, said: "This work builds on what we already know.

"Lifestyle can affect your telomeres. It would be interesting to find out whether it is diet, stress or both that is important."