The suprachiasmatic nucleus, a cluster of roughly 20,000 neurons in the hypothalamus, serves as the body's master clock. It receives light signals and orchestrates hormone release, body temperature, and sleep-wake cycles. This clock runs on an approximately 24-hour cycle.
Morning light suppresses melatonin and triggers cortisol. Blue spectrum light after sunset delays melatonin release, shifting your cycle later. This is why screen use before bed correlates with difficulty falling asleep.
Roughly 40% of people are morning types, 30% are evening types, and 30% fall in between. These chronotypes are partly genetic. Forcing a night owl to be productive at 7 AM is biologically counterproductive.
Your circadian rhythm is a biological system that governs energy, cognition, and health. Aligning your schedule with your internal clock requires consistency: regular light exposure, sleep timing, and meal timing.