Many physiological processes and behaviours follow an approximate 24h pattern called a circadian rhythm, which are primarily entrained by the daily cycle of light and dark. Robust circadian rhythms are important for health, including our mood, metabolism and immune system. However, circadian rhythms become blunted with ageing. This briefing considers whether time-restricted feeding could replace light as the main ‘entrainer’ and be used to restore circadian rhythms in old age.