Age-related differences in circadian timing system and sleep quality in young and older lifelong endurance runners

Robustness of circadian rhythms decreases with age, contributing to age-related functional deficits, including those affecting the sleep-wake cycle. While exercise can acutely impact the circadian clock, potential long-term benefits have received little attention. Here, we investigated whether lifelong endurance running can mitigate age-related circadian decline and improve sleep quality. The study included 39 male participants, categorised according to their running practice and age as young (YR, 20-30 years) and older (OR, 65-78 years) endurance runners and age-matched young (YC) and older (OC) untrained controls. Improved sleep efficiency and less fragmented sleep were observed in OR than OC, whereas the opposite was found between YR and YC. These effects were independent of melatonin production, as urinary 6-sulfatoxymelatonin levels were elevated in runners in both age categories. The rest-activity rhythm amplitude was higher in runners than in their untrained counterparts. Total daily activity did not differ between OR and OC but was higher in YR than YC. Furthermore, YR exhibited the least robust rest-activity rhythm, with low inter-daily stability and high intra-daily variability. Together, lifelong endurance running can modulate the link between the circadian system and sleep quality, but these effects differ and are not equally beneficial for young and older men.