Sleep Medicine Circadian Rhythm
What is a Circadian Rhythm?
We all have an internal clock that regulates our cycle of sleep and wake around a 24 hour period. Our internal clock allows us to sleep at night and remain awake during the day time. Some people’s internal clocks predispose them to being night owls (staying up late and waking up late) while others tend to be morning larks (going to bed early and waking up early). While we can change our behaviors and our sleep schedule to try and adjust our internal clock, setting your sleep and wake times in accordance with your natural internal rhythm provides the most refreshing and satisfying sleep. Unfortunately, life’s demands such as school and work start times do not always allow us to adhere to our preferred sleep schedules. The internal clock works best when we maintain a regular sleep schedule including regular wake times and exposure to light upon awakening.
Circadian rhythms can sometimes become disrupted for various reasons, most commonly shift work and jet lag. The most common types of circadian rhythm sleep disorders are:
- Delayed sleep phase syndrome
- Advanced sleep phase syndrome
- Shift work disorder
- Jet lag
You can read more about these disorders and their treatments below.
Delayed Sleep Phase Syndrome
Delayed Sleep Phase Syndrome is characterized by habitual sleep-wake times that are delayed, usually more than two hours, relative to conventional or socially acceptable times. Affected individuals complain of difficulty falling asleep at a socially acceptable time, but once sleep ensues, sleep is usually normal. A typical patient has difficulty initiating sleep, generally falling asleep after midnight, and prefers late wake-up times. Attempts to fall asleep earlier are usually unsuccessful. Many teenagers and young adults suffer from this problem, often resulting in difficulty getting to school on time or being late for work. Having a delayed internal clock is only a problem if it causes impairment in ability to function (including social or occupational dysfunction). This condition can be treated, but it requires significant patience and motivation.
The main treatments for Delayed Sleep Phase Syndrome include a combination of Light Therapy and Chronotherapy. Treatment recommendations include at least 30 minutes of bright light exposure in the morning and avoiding light exposure in the evening. Every effort should be made to keep the same wake up time every day, even on weekends. Chronotherapy aims to reset the circadian clock by slowly delaying the bedtime (and hence the sleep period) by about two hours every few days. Chronotherapy can be very disruptive to one’s daily schedule during the times when day and night are essentially reversed so this treatment is less frequently used.
Advanced Sleep Phase Syndrome
Advanced Sleep Phase Syndrome is characterized by habitual sleep onset and wake-up times that are several hours earlier relative to conventional and desired times. Affected individuals complain of sleepiness in the late afternoon or early evening, early sleep onset, and spontaneous early morning awakening. Individuals typically complain of early morning insomnia and excessive evening sleepiness. When patients are allowed to maintain an advanced schedule, their sleep is usually normal for age. This condition often occurs in elderly people.
Advanced Sleep Phase does not need to be treated unless it is affecting ability to function. The main treatment for advanced sleep phase syndrome involves evening light exposure to help delay the biological clock. This may be natural outdoor light or artificial light such as a 10,000 lux light box for 30-90 minutes in the evening.
Shift Work Sleep Disorder
Shift Work Sleep Disorder is characterized by complaints of insomnia or excessive sleepiness that occur in relation to work hours that are scheduled during the usual sleep period. There are several types of shift-work schedules, including night shifts, early morning shifts, and rotating shifts. The sleep disturbance is most commonly reported in association with the night and early morning shifts. Total sleep time is typically curtailed by one to four hours in night and early morning shift workers, and sleep quality is perceived as unsatisfactory. In addition to impairment of performance at work, reduced alertness may also be associated with consequences for safety. The sleep disorder occurs despite attempts to optimize environmental conditions for sleep. The condition usually persists for the duration of the work-shift period. However, in some individuals, the sleep disturbance may persist beyond the duration of shift work.
Improving the sleep of a shift worker with sleep difficulties often involves finding practical solutions to help strengthen the patient’s circadian rhythms for sleep and wake during desired time. For example, night shift workers should wear sunglasses on the morning commute home to reduce light exposure and improve the ability to sleep upon arrival home. Properly timed dim and bright light exposure can be a helpful tool as well.
Jet Lag
Jet Lag is a circadian rhythm sleep disorder in which there is a temporary mismatch between the timing of the sleep and wake cycle generated by the endogenous circadian clock and that of the sleep and wake pattern required by a change in time zone. Individuals complain of disturbed sleep, decreased subjective alertness, and impaired daytime function. The severity of symptoms is dependent on the number of time zones traveled and the direction of the travel. Eastward travel (requiring advancing circadian rhythms and sleep-wake hours) is usually more difficult to adjust to than westward travel.
Treatment for Jet Lag is usually not necessary for short trips. Adjustments to one’s sleep schedule before and during travel as well as use of hypnotic medications can assist with decreasing jet lag.
