By Naomi Carr
Updated: 22 February 2024 & medically reviewed by Morgan Blair
Circadian rhythms are the internal body clocks we all have that help regulate physical and cognitive functions, sleep, and mood. These functions play a big part in maintaining physical and mental well-being, so disruptions to our circadian rhythms can have a significant impact on mood and health.
Table of contents:
What are circadian rhythms?
Circadian rhythms are internal 24-hour clocks that regulate numerous functions in the body. The circadian rhythm most commonly referred to is the sleep-wake cycle, which tells the body when to be awake and alert and when to sleep. Other circadian rhythms include regulating several bodily and cognitive functions, which can impact physical and mental health. [1]
How do circadian rhythms work?
The brain controls circadian rhythms in an area called the hypothalamus. This area sends information to the rest of the body to regulate functions such as emotions, organ functioning, digestion, temperature, and alertness. [2][3]
Various environmental cues impact the circadian rhythms, including activity, temperature, and food consumption. The most significant impact on the circadian rhythms is light and dark exposure. This can impact various functions, especially the sleep-wake cycle. [1][4]
What is circadian rhythm disorder?
There are several types of circadian rhythm disorders, that impact the sleep-wake cycle. This occurs when the 24 hours of the circadian rhythm do not match up with the individual’s environment, and cause significant impacts on sleep and functioning. [1]
Circadian rhythm disorders can be temporary and may be related to work or travel. Alternatively, they might be more persistent and could be related to genetic or medical causes. Persistent circadian rhythm disorders are likely to require a professional diagnosis and treatment, to prevent severe and long-lasting adverse effects. [4]
Circadian rhythm disorders can cause: [2]
Excessive daytime drowsiness
Impaired concentration
Decreased alertness
Poor memory
Impaired decision-making
Mood changes
Impaired daily functioning
What happens when the circadian rhythm is off?
Irregular circadian rhythms can impact many functions and may cause detrimental effects on mental and physical well-being, such as: [2][3][5]
Reduced sleep quality and quantity, including difficulties falling asleep and staying asleep, waking earlier, and shallow sleep
Inability to regulate mood, potentially leading to the onset or worsening of mental health conditions such as anxiety, depression, and bipolar disorder
Changes in metabolism and weight, through sugar and cholesterol regulation
Changes in appetite, due to disruptions in the digestive system or changes to meal times
Impaired temperature regulation
Impaired immune system and body repair abilities
How do circadian rhythms affect sleep?
Circadian rhythms are strongly associated with sleep. Having an irregular circadian rhythm can cause significant disruptions in sleep quality and quantity. This can impact how quickly we fall asleep, whether we can sleep through the night without waking up, and how early we wake up in the morning. [1]
The sleep-wake cycle is significantly impacted by light and dark. Exposure to sunlight signals the brain and body to be alert and awake, while darkness causes the release of melatonin, causing us to feel sleepy. If circadian rhythms are disrupted by changes in light and dark exposure, these signals can become altered, causing daytime sleepiness and insomnia. [6]
Trying to sleep outside of our natural circadian rhythms, whether due to work, travel, genetics, or medical reasons, can also cause daytime drowsiness, insomnia, and other sleep disturbances, and changes in the quality of various sleep phases, such as having more shallow and non-restorative sleep. [1]
Although the sleep-wake cycle is mostly affected by light, some people have different circadian rhythms due to age or genetics. For example, adolescents are likely to be ‘night owls’, causing them to become sleepy later at night and to sleep later in the mornings. As we get older, this adjusts, and adults are more likely to sleep earlier in the evenings and wake earlier in the mornings. [5][6]
How do circadian rhythms affect mental health?
As mentioned, circadian rhythms affect several functions in the body, which have an impact on physical and mental well-being. When these functions are disrupted, it can cause the onset or worsening of various mental health symptoms. [2][7]
For example, when sleep is disrupted, symptoms of anxiety and depression are often worsened. Studies have found that depression is more likely in those whose sleep patterns do not match their circadian rhythms. Conversely, depression can cause circadian rhythm irregularities, contributing to worse sleep and functioning. [2][8]
When people are out of sync with their circadian rhythms, they are likely to experience excessive tiredness, impaired functioning, and physical pains or issues such as stomach or bowel irregularities. This can contribute to increased feelings of stress and worry, along with poor mood regulation. [5]
Healthy circadian rhythms can help with mood regulation and resilience to challenging situations and emotions. Studies suggest that different circadian rhythms have different impacts on mood. For example, ‘night owls’, or people who are more active later in the day and sleep later at night, are more likely to be susceptible to symptoms of anxiety and depression than those who wake early. [6]
What can disrupt circadian rhythms?
Jet lag: Traveling across different time zones can have a significant impact on circadian rhythms and can cause changes to appetite, irregular bowel movements, mood changes, and excessive fatigue.
Night shifts: Working night shifts or irregular patterns can disrupt circadian rhythms, particularly if there is no natural light exposure for many days or weeks. Disruptions include sleep, appetite, temperature regulation, mood, and digestion. Studies have found that night shift workers are 40% more likely to experience depression. [9]
Artificial light at night: Using smartphones or watching television late at night can alter the release of melatonin caused by darkness. This can disrupt the sleep-wake cycle, as the brain does not signal to the body that it is time to sleep, thereby contributing to insomnia or trouble falling asleep.
Lack of sunlight: When we are not exposed to much natural sunlight, such as during dark winters or spending a lot of time indoors, our circadian rhythms can become disrupted. As sunlight causes a signal to be alert and awake, a lack of sunlight can cause daytime sleepiness, changes in sleep schedules, and low mood.
Urban areas: Studies have found that individuals living in urban areas are more likely to have disrupted circadian rhythms due to noise and light pollution at night. This can cause increases in stress and poor sleep quality. [2]
Non-24-hour sleep-wake disorder: Primarily affecting blind people, non-24-hour sleep-wake disorder is caused by an inability to receive light cues that regulate the circadian rhythms. This can cause the sleep-wake cycle to adjust from day to day.
Irregular sleep-wake rhythm disorder: Irregular sleep-wake rhythm disorder can be caused by brain injury or conditions such as dementia. It can cause the sleep-wake cycle to be dysregulated, thus causing inconsistent sleep patterns, such as regular napping throughout the day.
How to maintain a healthy circadian rhythm
To maintain a healthy circadian rhythm it is important to implement good sleep hygiene practices. This can include: [1][4][5]
Reducing artificial light at night, so not using smartphones or watching television before going to bed
Getting plenty of exposure to natural light during the day, particularly first thing in the morning
Forming and maintaining a sleep schedule, going to bed and waking up at the same time each day
Engaging in calming and relaxing activities before bed, such as reading, meditating, or taking a bath
Ensuring you get around eight hours of sleep every night
Avoiding caffeine in the late afternoon and evening
Avoiding or limiting naps during the day
Ensuring your bedroom is dark and quiet while you sleep
Exercising in the daytime
If you experience consistent issues with your circadian rhythm, even after implementing these techniques, it may be necessary to consult with a doctor as you may require professional intervention. Many physical and mental health issues that are caused or worsened by irregular sleep patterns can be reversed or alleviated by reestablishing the circadian rhythm. [7]
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