The circadian rhythm is the body's internal 24-hour clock that regulates the sleep-wake cycle and many other physiological processes. It is controlled primarily by a region of the brain called the suprachiasmatic nucleus, which responds to light and darkness signals from the eyes.
Consistent sleep and wake times (even at weekends) are the single most important factor. Morning daylight exposure anchors the rhythm. Avoiding bright light (especially screen blue light) in the evening prevents melatonin suppression. Disrupted circadian rhythms — from shift work, jet lag, or irregular schedules — are associated with poorer sleep, mood and metabolic health.