Published: June 05, 2026, 14:32 UTC
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title: “Lifelong Running Preserves Circadian Health in Older Men, But Young Runners May Pay a Sleep Cost”
post_status: draft
post_author: 1
post_category: sleep
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Kosice — It is well established that circadian rhythms weaken with age. Sleep becomes more fragmented, the daily rest-activity cycle loses its sharpness, and melatonin output declines. Exercise is known to benefit sleep in the short term, but whether a lifetime of endurance training can hold back age-related circadian decline has remained unclear.
A new study in Scientific Reports suggests the answer is more complicated than a simple “yes.”
Researchers led by Katarina Kovacova at the Institute of Experimental Physics in Kosice, Slovakia, recruited 39 men divided into four groups: young runners (aged 20-30), older runners (65-78), and age-matched untrained controls for both categories. The runners were lifelong endurance athletes who had maintained regular training for decades. Each participant wore wrist actigraphy for monitoring rest-activity rhythms, provided urine samples for melatonin metabolite (6-sulfatoxymelatonin) measurement, and completed sleep quality assessments.
The results revealed a striking age-by-exercise interaction. Among older participants, lifelong runners showed significantly better sleep efficiency and less fragmented sleep than their sedentary peers. Their rest-activity rhythm amplitude was higher, meaning the contrast between daytime activity and nighttime rest was sharper, a hallmark of a robust circadian system. Melatonin levels were also elevated in both young and older runners compared to controls, suggesting running preserves the pineal gland’s output regardless of age.
But the findings in young runners were unexpected. Compared to young controls, young endurance runners showed the least robust rest-activity rhythms of any group, with low inter-daily stability and high intra-daily variability. Their sleep efficiency was lower, not higher, than their sedentary counterparts.
The authors interpret this as a potential cost of high training volume. Young runners accumulate far more total daily activity than older runners or controls, and this elevated physical load may fragment their sleep-wake cycle rather than consolidate it. In older runners, total daily activity did not differ from age-matched controls, suggesting the circadian benefits emerge from the regularity of exercise over decades, not from sheer volume.
A key finding was that these effects were independent of melatonin production. Both young and older runners had elevated urinary 6-sulfatoxymelatonin, indicating better pineal function. Yet sleep outcomes diverged by age, meaning melatonin alone does not determine sleep quality.
The study has clear limitations. The sample was small (39 men) and exclusively male. The cross-sectional design cannot prove causation, and unmeasured differences in lifestyle, genetics, or training intensity could contribute to the observed patterns.
For the general reader, the takeaway is that lifelong endurance exercise appears to buffer the circadian system against aging, but the relationship is not uniform. Older runners benefit clearly; younger athletes training at high volumes may experience a different trade-off between performance and sleep.
Source: Kovacova K, Berisha G, Stebelova K, et al. Age-related differences in circadian timing system and sleep quality in young and older lifelong endurance runners. Scientific Reports, 2026. DOI: 10.1038/s41598-026-56087-3