Circadian Rhythm

The circadian rhythm, often referred to as the body's internal clock, is a roughly 24-hour cycle that regulates various physiological processes in living organisms, including humans. These rhythms influence sleep-wake cycles, hormone release, body temperature, appetite, and other important bodily functions.

Here's a breakdown of key aspects of circadian rhythms:

What they are:

• Circadian rhythms are endogenous, meaning they originate within the organism.
• They oscillate with a period of approximately 24 hours. The term "circadian" comes from the Latin "circa" (about) and "dies" (day).
• These rhythms are found in most living things, including animals, plants, and microorganisms.
• In humans, nearly every tissue and organ has its own circadian rhythm, all coordinated by a master clock in the brain.

How they work:

• The master clock in humans is located in the suprachiasmatic nucleus (SCN), a group of nerve cells in the hypothalamus.
• The SCN receives light signals from the eyes, which is the primary environmental cue (called a zeitgeber, meaning "time giver") that synchronizes the internal clock with the external day-night cycle.
• Based on light exposure, the SCN controls the production of hormones like melatonin, which promotes sleepiness in the evening, and cortisol, which promotes alertness in the morning.
• Other zeitgebers besides light include food intake, stress, physical activity, social environment, and temperature.
• At a cellular level, circadian rhythms involve complex feedback loops of "clock genes" and their protein products, which regulate gene expression and cellular functions throughout the day.

Importance of circadian rhythms:

• They ensure that the body's processes are optimally timed for the 24-hour cycle.
• They play a crucial role in regulating sleep patterns, allowing for restorative processes during the night and wakefulness during the day.
• They influence hormone release, which affects various bodily functions, including metabolism and stress response.
• They impact appetite and digestion, coordinating these processes with typical eating times.
• They contribute to regulating body temperature, which fluctuates throughout the day.

Disruptions to circadian rhythms:

When the internal clock is misaligned with the external environment or when the internal clock itself malfunctions, it can lead to circadian rhythm sleep disorders. Common examples include:

• Jet lag disorder: Occurs when traveling across multiple time zones, causing a mismatch between the body's internal clock and the new environment's light-dark cycle.
• Shift work disorder: Affects individuals who work non-traditional hours (e.g., night shifts), forcing them to be awake when their body's clock is signaling sleep.
• Delayed sleep-wake phase disorder (DSWPD): Characterized by a consistent pattern of late sleep onset and wake times.
• Advanced sleep-wake phase disorder (ASWPD): Characterized by a consistent pattern of early sleep onset and wake times.
• Irregular sleep-wake rhythm disorder: Involves unpredictable and inconsistent sleep-wake cycles throughout the day.
• Non-24-hour sleep-wake rhythm disorder: The sleep-wake cycle drifts later each day, not aligning with the 24-hour day.

Consequences of circadian rhythm disruption:

Short-term disruptions can lead to:

• Drowsiness and fatigue
• Poor coordination
• Difficulty with learning and focus
• Changes in mood
• Digestive issues

Long-term, chronic disruption of circadian rhythms has been linked to an increased risk of:

• Obesity
• Diabetes
• Mood disorders (e.g., depression, bipolar disorder, seasonal affective disorder)
• Heart and blood pressure problems
• Cancer
• Worsening of existing health issues

Maintaining a healthy circadian rhythm:

• Establish a regular sleep schedule: Go to bed and wake up around the same time each day, even on weekends.
• Maximize natural light exposure during the day: Spend time outdoors, especially in the morning.
• Minimize artificial light exposure in the evening: Avoid bright screens (phones, tablets, computers, TVs) in the hours leading up to bedtime.
• Create a comfortable sleep environment: Ensure the bedroom is dark, quiet, and cool.
• Practice good sleep hygiene: Avoid caffeine and alcohol close to bedtime, do not take long naps late in the day, and engage in relaxing pre-sleep routines.
• Maintain a regular meal schedule: Eating at consistent times can help regulate your body's internal clock.
• Engage in regular physical activity: Exercise can improve sleep quality, but avoid intense workouts close to bedtime.

Understanding and respecting the body's circadian rhythm is essential for overall health, well-being, and optimal functioning. If you suspect you have a circadian rhythm sleep disorder, it's advisable to consult with a healthcare professional for diagnosis and appropriate management strategies.

Reference: Dr. Anthony Goldsmith, Australia

Author

Paddy Kalish OD, JD and B.Arch Author and Blogger