Circadian Rhythm Disorders

Circadian rhythm disorders occur when the so-called "internal clock" that regulates sleep and wakefulness is not synchronized with the environment.

The circadian rhythm follows a 24-hour cycle, which usually adjusts to external cues, such as the presence of darkness or light. This internal clock is regulated by the brain and is stimulated by light reaching the retina, which generates nerve impulses that help stop the production of melatonin (the hormone that induces sleep). When the internal rhythm is not aligned with the environment in which a person lives, sleep difficulties and disturbances occur.

Depending on individual preferences, there are three basic chronotypes:

• Morning-type: They prefer daytime hours, so they tend to wake up early and go to bed early.
• Evening-type: Night owls who go to bed and wake up late.
• Standard: They easily adapt to waking up early or staying up late according to changes in their environment. Generally, they begin to secrete melatonin at a time between the morning and evening types. The majority of people belong to this group.

Under normal conditions, people can adjust to the environment's needs without much difficulty. Circadian rhythm disorders manifest when it is impossible or takes too long for the body to adjust to the change. The most common sleep-wake disorders are:

• Jet lag: Time zone differences caused by a sudden shift in time zones.
• Shift work disorder: This worsens when alternating between daytime and nighttime shifts without a consistent schedule. Continuous night shifts tend to show fewer symptoms, although sleeping during the day is often challenging due to light and external noise.
• Delayed sleep phase disorder: More common in adolescents, who cannot fall asleep early despite trying, making it almost impossible to wake up in the morning. They go to bed late and wake up late, which can lead to tardiness or absences from work or school.
• Advanced sleep phase disorder: Often occurs in older adults, who cannot change the routine of going to bed and waking up early. They go to bed early and wake up early. Sometimes, they wake up excessively early, which can be mistaken for insomnia.
• Non-24-hour sleep-wake disorder: The cycle shifts from day to day. In other words, even though the same number of hours of sleep is maintained, the time of going to bed or waking up changes constantly. It is rare and most common among blind people.

Symptoms

The most characteristic indicator of circadian rhythm disorders is the inability to sleep when needed. This leads to other symptoms such as:

• Daytime sleepiness
• Lack of concentration
• Difficulty thinking
• Problems carrying out daily tasks
• Irritability
• Excessive use of alcohol or stimulants
• Poor academic or work performance

Causes

The causes of circadian rhythm disorders can be divided into two types:

• Internal: Physical conditions or abnormalities such as brain injuries, Alzheimer's, head trauma, or blindness.
• External: Changes in time zones, irregular work shifts, frequent changes in sleep routine, certain medications, especially those containing melatonin.

Risk Factors

Factors that increase the risk of suffering from a circadian rhythm disorder include:

• Age: The internal clock changes with age, delaying in adolescence and advancing in old age.
• Genetic predisposition
• Work schedule: Rotating shifts contribute to the onset of these disorders.
• Frequent travel across time zones
• Consumption of alcohol, stimulants, or illegal drugs
• Certain diseases: Autism, depression, bipolar disorder, Parkinson's, Alzheimer's, blindness, macular degeneration, or Angelman syndrome.
• Hormonal changes: Women may experience these disorders during pregnancy and menopause.
• Exposure to artificial light at night

Complications

When sleep-wake disorders persist over time, they can lead to:

• Irritability
• Concentration problems
• Decreased alertness
• Fatigue
• Daytime sleepiness
• Poor work or academic performance
• Memory loss

Prevention

Although it may be impossible to prevent some circadian rhythm disorders, symptoms of some types can be reduced by following these guidelines:

• Maintain good sleep hygiene by keeping consistent schedules every day. For night workers, it is recommended to follow the same routine on their days off.
• Limit screen usage and exposure to blue light before bed.
• Get natural sunlight every day.
• Align sleep and wake cycles with day and night hours when possible.

Which doctor treats circadian rhythm disorders?

Circadian rhythm disorders are treated at the sleep unit.