Circadian Rhythm Disruption

Circadian Rhythm Disorders: When the Internal Clock Gets Disrupted

Circadian rhythms are internal biological processes that follow an approximately 24‑hour cycle and regulate virtually every aspect of our physiology, from body temperature and hormone production to metabolism and, most importantly, the sleep‑wake cycle. The main “conductor” of these rhythms is a cluster of nerve cells in the hypothalamus called the suprachiasmatic nucleus. This internal clock synchronizes with the external world through light. Circadian rhythm disorders arise when there is a mismatch between this internal clock and the external environment or social demands.

How does our internal clock work?

The primary cue for synchronization is light, especially in the morning. When light hits the retina, it sends a signal to the brain to stop producing melatonin — the “sleep hormone”. This helps us wake up. In the evening, as darkness falls, melatonin production resumes, causing sleepiness.

Types and causes of circadian rhythm disorders

• Jet lag (time‑zone shift syndrome): A temporary disorder that occurs when crossing several time zones quickly. The internal clock remains set to the “home” time.
• Shift‑work disorder: Occurs in people who work at night and are forced to sleep during the day, which conflicts with natural light‑and‑dark cues.
• Delayed sleep‑phase syndrome: Common among adolescents and young adults (“night owls”). Their internal clock is “lagging”. They cannot fall asleep until late night (2‑3 a.m.) and consequently find it hard to wake up in the morning.
• Advanced sleep‑phase syndrome: Common among older adults (“early birds”). They feel sleepy early in the evening and wake up very early in the morning.

Circadian rhythm disturbances lead to insomnia at night and excessive sleepiness during the day. Treatment involves light therapy and melatonin therapy aimed at “re‑setting” the internal clock.