Circadian rhythms are intrinsic ~24-hour biological cycles that coordinate sleep–wake patterns, hormone secretion, metabolism, temperature, and behaviour across nearly all forms of life, and in mammals they are orchestrated by the suprachiasmatic nucleus (SCN) of the hypothalamus, first identified as the master pacemaker through lesion and transplantation studies by Robert Y. Moore and Victor B. Eichler (1972), later refined by genetic discoveries from Jeffrey C. Hall, Michael Rosbash, and Michael W. Young (1984, Nobel Prize 2017), and built upon earlier chronobiological insights by Jürgen Aschoff and Colin S. Pittendrigh in the mid-20th century. The SCN, a paired structure of roughly 20,000 neurons situated above the optic chiasm, receives photic input from intrinsically photosensitive retinal ganglion cells via the retinohypothalamic tract, synchronizes peripheral clocks through neural and hormonal signals (including regulation of melatonin by the pineal gland), and maintains rhythmic gene expression through transcription–translation feedback loops involving core clock genes (e.g., PER, TIM, CLOCK), thereby aligning internal physiology with the external light–dark cycle.

From a Christian perspective, circadian order reflects the created rhythm embedded in Genesis 1 (“there was evening and there was morning”) and the Sabbath principle of patterned work and rest (Exod. 20:8–11), suggesting that biological timekeeping is not accidental but consonant with a theological vision of creation structured by divine wisdom (cf. Ps. 104:19), so that honouring bodily rhythms through regular sleep, light exposure, and rest practices becomes both stewardship of the body (1 Cor. 6:19–20) and participation in God’s ordered design.

Practically, circadian science has profound value for personal wellbeing, improving sleep quality, mood regulation, metabolic health, and cognitive performance, and for societal health by informing school start times, shift-work policies, hospital scheduling, and public health strategies that reduce accidents, chronic disease burden, and healthcare costs, demonstrating how rigorous neuroscience and genetic research can serve human flourishing at both individual and communal levels.