What is the primary regulator of the body's circadian rhythms?

The primary regulator of the body’s circadian rhythms is melatonin. This hormone is produced by the pineal gland in response to darkness, signaling the body that it is time to sleep. Melatonin levels naturally rise in the evening and peak during the night, promoting sleepiness and helping to regulate the sleep-wake cycle, which is a key component of the circadian rhythms.

Cortisol, while an important hormone involved in the sleep-wake cycle, primarily plays a role in the body's response to stress and helps regulate metabolism, blood sugar, and immune responses rather than directly governing circadian rhythms. Serotonin contributes to mood regulation and is a precursor to melatonin, but it is not the primary regulator of sleep cycles. Adrenaline primarily prepares the body for 'fight or flight' responses and is not involved in regulating circadian rhythms. Thus, melatonin is the most critical hormone associated with maintaining our natural circadian patterns.