The small study involved 30 men with low-risk prostate cancer who underwent three months of lifestyle changes.
They had blood levels of the enzyme telomerase 29 percent higher after these three months than when they began.
Telomerase repairs and lengthens telomeres, which cap and protect the ends of chromosomes housing DNA.
The study's lead researcher, 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.
The lifestyle changes in the study 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, reports BBC.
Among the 24 men who had sufficient data for analysis, blood levels of telomerase increased by 29 percent on average, the research found.
Increases in telomerase activity were linked with decreases in "bad" LDL cholesterol and decreases in one measure of stress - intrusive thoughts.
"This might be a powerful motivator for many people to beneficially change their diet and lifestyle," the researchers told The Lancet Oncology.
Professor Tim Spector, from King's College London, who has been researching ageing 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."