Aerobic exercise (120 minutes per week) significantly lengthened telomeres, a biomarker for healthy aging, in white blood cells after 24 weeks in previously inactive, highly stressed older adults (randomized controlled trial).

Many other observational studies have found associations between physical activity and telomere length but this study was able to establish causation. The enzyme that is able to rebuild and lengthen telomeres, called telomerase remained unchanged and so it remains unclear how physical activity was able to increase telomere length in these individuals. Very interesting observation that will hopefully lead to future randomized controlled trials.