Circadian rhythms and microbiota: molecular crosstalk and its implications for health and disease.

Circadian rhythms, evolutionarily conserved 24-hour oscillations, exert precise regulatory control over microbial communities across host niches including the gastrointestinal tract, oral cavity, urinary bladder, and skin. This bidirectional interplay is critical to host physiology: host circadian clocks shape the composition and functional rhythms of resident microbiota, while microbiota-derived signals reciprocally modulate circadian entrainment and tissue-specific rhythmicity. Circadian disruption from shift work, irregular feeding, light pollution, or sleep deprivation trigger microbial dysbiosis and circadian misalignment, contributing to metabolic diseases, gastrointestinal disorders, neuropsychiatric conditions, cardiovascular diseases, and dermatological or reproductive disorders. Mechanistically, this crosstalk is mediated by rhythmic hormonal secretion, microbial metabolites, epigenetic regulation, and immune signaling. Therapeutic strategies such as time-restricted feeding, probiotics, melatonin, and polyphenol-rich diets show promise in restoring temporal homeostasis. This review synthesizes current evidence on circadian-microbiota interplay, elucidates its roles in physiology and disease, and highlights translational opportunities for chrono-microbiome-based interventions to optimize host health.