The circadian rhythm is largely independent of external factors that could indicate the time of day, night or even the season. It helps us to orient ourselves to the time and to carry out periodic activities, such as sleeping, eating, hibernating, reproducing, etc., in a relatively constant rhythm. Due to the changing length of the day - as a result of the changing seasons - a constant resynchronization of the internal clock is necessary. Nowadays, however, the circadian rhythm often has to be resynchronized at very short notice due to a rapid change in geographical location, e.g. after a transatlantic flight, the consequence of an initial lack of synchronization is the well-known jet lag.
The disease group is characterized by a lack of synchronization of the intrinsic circadian rhythm with the light-dark alternation. Either the intrinsic pacemaker itself is disturbed or the sleep-wake rhythm deviates from a normal intrinsic circadian rhythm due to external factors.
Insomnia (difficulty falling asleep or staying asleep) or hypersomnia (constant sleep addiction) or both are the result. If the affected person is able to align their sleep times with their internal rhythm, the duration and quality of sleep are normal, as is performance during the waking phase. Sleep disorders are most common in shift work, with negative health effects and reduced performance at work. Sleep diaries are the basis for diagnosis, and strict adherence to fixed bedtimes in conjunction with light therapy are the basis for treatment.
Healthy maintenance of the circadian rhythm
Although we don't have complete control over our circadian rhythm, there are tips for healthy sleep that we can use to try to better manage our 24-hour sleep cycles
Get some sun: Exposure to natural light, especially early in the day, helps to reinforce the strongest circadian cue.
Follow a consistent sleep schedule: Varying your bedtime or morning wake-up time can interfere with your body's ability to adjust to a stable circadian rhythm.
Move daily: Activity during the day can support your internal clock and help you fall asleep more easily at night.
Avoid caffeine: Stimulants such as caffeine can keep you awake and upset the natural balance between sleep and wakefulness. Everyone is different, but if you have trouble sleeping, you should avoid caffeine after midday.
Limit the amount of light before bed: Exposure to artificial light at night can disrupt circadian rhythms. Experts advise dimming the lights and putting away electronic devices before bedtime, keeping them out of the bedroom and away from the sleep surface.
Keep naps short and early in the afternoon: Late and long naps can push bedtime back and throw your sleep rhythm off balance.
These steps to improve sleep hygiene can be an important part of supporting a healthy circadian rhythm, but other steps may be necessary depending on your situation. If you have persistent or severe sleep problems, daytime sleepiness and/or a problematic sleep rhythm, it's important to speak to a doctor who can best diagnose the cause and offer the most appropriate treatment.
Disorders of the circadian rhythm
In circadian rhythm disorders, the endogenous sleep-wake rhythm (internal clock) and the external light-dark cycle are offset (desynchronization). The cause can be endogenous (e.g. delayed or advanced sleep phase syndrome) or external (e.g. jet lag, shift work).
If the cause is external, other circadian rhythms in the body, including temperature and hormone secretion, can become asynchronous with the light-dark cycle (external desynchronization) and with each other (internal desynchronization); in addition to insomnia and excessive sleepiness, these changes can lead to nausea, malaise, irritability and depression.
The risk of cardiovascular disease and metabolic disorders may also be increased. It is particularly difficult to adapt to repeated circadian shifts (e.g. due to frequent long-distance travel or rotating shift work), especially when shifts change in the counterclockwise direction. Counterclockwise shifts are those that move wake and sleep times forward (e.g. flying east, shifts that rotate from day to night to evening). The symptoms subside after a few days or, in some patients (e.g. older people), after a few weeks or months, while the rhythms readjust.
Because light is a strong synchronizer of circadian rhythms, exposure to bright light (sunlight or artificial light with an intensity of 5000-10,000 lux) after the desired wake-up time and the use of sunglasses before the desired bedtime accelerate readjustment.
Patients with circadian rhythm disorders often abuse alcohol, hypnotics and stimulants.
Effects of a disturbed rhythm
If the circadian rhythm is disturbed, this means that the body's systems are not functioning optimally.
A disrupted circadian sleep-wake rhythm can lead to serious sleep problems. Without the proper signals from the body's internal clock, a person may have difficulty falling asleep while waking during the night or not be able to sleep as long as they would like until morning. Overall sleep may be reduced, and a disrupted circadian rhythm can also mean shallower, fragmented and poorer quality sleep.
In addition, studies have identified circadian rhythm disruption as a possible cause of obstructive sleep apnea (OSA), a sleep disorder characterized by repeated pauses in breathing. OSA reduces the body's oxygen levels and causes numerous sleep interruptions during the night.
Given the important role of sleep in productivity and overall health, a disrupted circadian rhythm often has significant consequences. Overall, a misaligned circadian rhythm can negatively impact sleep in many ways, increasing the risk of insomnia and excessive daytime sleepiness.
