What hormone regulates the sleep-wake cycle?

Melatonin is the hormone primarily responsible for regulating the sleep-wake cycle, also known as the circadian rhythm. It is secreted by the pineal gland in response to darkness, signaling to the body that it is time to prepare for sleep. Melatonin levels typically rise in the evening, peak during the night, and fall in the morning, which helps facilitate the transition between sleep and wakefulness.

The importance of melatonin in sleep regulation stems from its role in promoting sleepiness and influencing the timing of biological rhythms. This is critical for maintaining a regular sleep schedule and overall health.

Cortisol, on the other hand, is associated with wakefulness and is often referred to as the stress hormone, while serotonin is more involved in mood regulation and has a role in sleep but is not the primary regulator. Dopamine is primarily linked to reward and motivation rather than directly affecting the sleep-wake cycle. Thus, while all these hormones play significant roles in various physiological processes, melatonin is specifically recognized for its direct influence on managing sleep patterns.