Which hormone is associated with darkness and sleep?

• A. Melatonin.
• B. Cortisol
• C. Adrenaline
• D. Dopamine

Answer: (A)

Darkness and sleep are governed by melatonin. This hormone is produced by the pineal gland and is closely tied to the body’s circadian clock. When light levels drop, signals from the retina travel to the brain’s clock (the suprachiasmatic nucleus), which then prompts the pineal gland to release melatonin. The resulting rise in melatonin helps you feel sleepy and lowers the body’s alertness for sleep. Light, especially blue light, suppresses melatonin, helping you wake up.

In contrast, cortisol is tied to waking and stress responses, with levels typically higher in the morning to promote alertness. Adrenaline is part of the fight-or-flight system and boosts immediate arousal, not a darkness-driven sleep signal. Dopamine influences reward and motivation and is not the primary driver of sleep in darkness.

So, the hormone most directly associated with darkness and sleep is melatonin.