When your body's internal clock is out of sync—like from shift work or jet lag—it messes up your stress hormones, stops your sleep hormone from working right, and turns on inflammation in the same way that being tired or stressed for a long time does.

Your body's stress hormone, cortisol, needs to go down at night so your sleep hormone, melatonin, can rise and help you fall asleep.

When animals like mice or rats have their sleep-wake cycles messed up for a long time—like from constant light or frequent time zone changes—it messes up their stress hormones, makes them less able to handle sudden stress, and leads to problems like weight gain, mood issues, and aging faster.

Working irregular shifts messes up your body clock, which makes it harder to sleep well. Poor sleep raises a stress hormone called cortisol, which then makes your sleep and heart function even worse over time — raising your risk of heart problems.

Cortisol secretion follows a circadian rhythm entrained primarily by environmental light exposure, with secondary modulation by feeding timing and psychological stress.

Your body naturally produces melatonin on a daily schedule controlled by light, with the highest levels in the middle of the night and very low levels during the day. This hormone acts like a master switch for your internal clock by binding to specific receptors in the brain to regulate sleep, while also influencing your immune system and heart health throughout your body.