The functional changes of the circadian system organization in aging

•The circadian clock is ubiquitous and conserved across a wide range of species.•The circadian clock is inherently linked to the mechanism of aging.•Breakdown of the circadian system is associated with age-related functional decline.•Aging impairs different components of the clock at central and peripheral levels.•Reinforcement of the clock is a possible strategy to benefit health and longevity.