Circadian Rhythm

A circadian rhythm is a roughly 24-hour internal biological cycle that regulates many of your body's processes, including the sleep-wake cycle, hormone release, body temperature, metabolism, and even immune function. The word 'circadian' comes from the Latin circa (about) and diem (day). These rhythms are driven by a master clock in the brain — a cluster of about 20,000 neurons called the suprachiasmatic nucleus (SCN), located in the hypothalamus just above where the optic nerves cross.

Your circadian clock is primarily synchronized by light exposure. When light enters your eyes, specialized photoreceptors in the retina send signals to the SCN, which coordinates the timing of biological processes throughout the body. In the morning, light signals suppress melatonin production and increase cortisol, promoting alertness. In the evening, diminishing light triggers melatonin release, preparing the body for sleep. This is why exposure to bright artificial light and screens at night can disrupt sleep — it confuses the circadian clock.

Circadian disruption has become a significant public health concern in modern society. Shift work, jet lag, irregular sleep schedules, and excessive nighttime light exposure can desynchronize the body's internal clocks, leading to sleep disorders, metabolic dysfunction, mood disturbances, weakened immunity, and increased risk of chronic diseases including obesity, diabetes, cardiovascular disease, and certain cancers.

Circadian rhythm disruption is now recognized as a contributor to numerous health conditions including insomnia, depression, bipolar disorder, metabolic syndrome, and cancer. If you struggle with sleep, your healthcare provider may evaluate your circadian patterns through sleep diaries, actigraphy (wrist-worn movement monitors), or measurement of dim-light melatonin onset.

Strategies for maintaining healthy circadian rhythms include consistent sleep and wake times (even on weekends), morning bright light exposure, limiting screen time in the 1-2 hours before bed, avoiding caffeine after early afternoon, and keeping your bedroom cool and dark. These practices, collectively known as sleep hygiene, are the first-line treatment for circadian-related sleep problems.