Which hormone is responsible for regulating the sleep-wake cycle?

The hormone responsible for regulating the sleep-wake cycle is melatonin. Melatonin is produced by the pineal gland in response to darkness, signaling the body that it is time to sleep. This hormone's levels typically rise in the evening, facilitating the onset of sleep, and fall in the morning, which helps promote wakefulness. It acts in tandem with the body's internal clock, or circadian rhythms, to maintain a regular sleep schedule and overall sleep quality.

Understanding the role of melatonin is crucial in the context of sleep disorders, jet lag, and the adjustments required when changing time zones. The other hormones mentioned, while important in various physiological roles, do not primarily influence the sleep-wake cycle in the same direct manner as melatonin does.