Melatonin as the master hormonal signal of darkness — and how modern light destroys it.
Produced by the pineal gland in response to darkness, melatonin is the primary humoral signal aligning physiology with the 24-hour day. MT1/MT2 receptors in the SCN receive this signal and coordinate cortisol, temperature, and sleep-wake timing across every organ system.
Even modest indoor lighting rapidly suppresses pineal melatonin. For night workers exiting shift into sunrise, this is a measured hormonal collapse — not a metaphor. Blue-blocking glasses and blackout environments are minimum viable armor.
Two systems drive sleep: sleep pressure (adenosine, builds with wakefulness) and sleep signaling (melatonin, temperature, cortisol). Night shift wedges them apart. Melatonin targets the signaling side — which is why timing matters more than dose paranoia.
Most melatonin is synthesized inside mitochondria as local antioxidant defense during ATP production. Circadian disruption isn't just "tired" — it's running cellular power plants without native fire suppression. Longevity deep dive →