Circadian Rhythm Disorders

Overview

If your internal biological clock is out of sync with your usual day-to-night cycle, a circadian rhythm disorder could be the cause. This internal misalignment with the environment results in sleep at the wrong times, or sleep that’s poor quality.

Your circadian rhythm is a 24-hour cycle of physical, mental, and behavioral changes influenced by light and regulated by your brain’s “master clock,” a large group of nerve cells called the suprachiasmatic nucleus (SCN). The SCN is in charge of alertness, hormones, metabolism, and brain signaling for your 24-hour sleep-wake cycle. When it’s misaligned, your brain and body are trying to function on the wrong schedule. Circadian rhythm disorders have become much more common in modern-day society due to artificial lighting, shift work, and global travel. Two of the most prevalent circadian rhythm disorders are shift work sleep disorder and jet lag disorder.

Shift Work Sleep Disorder

If you regularly work hours that overlap with the normal sleep period, shift work sleep disorder can occur. Symptoms of shift work sleep disorder can include excessive sleepiness at work, insomnia or difficulty when trying to sleep during the day, poor concentration or slower reaction time, and mood changes or irritability. 

Approximately 10%-20% of shift workers develop clinically significant symptoms of shift work sleep disorder, and doctors most commonly see it in healthcare workers, emergency responders, transportation workers, and hospitality and service workers. 

Jet Lag Disorder

After rapid travel across multiple time zones, jet lag disorder—or, more simply, jet lag—is common. Jet lag disorder happens because your internal clock still thinks you’re in the original time zone, which then triggers hunger cues and sleepiness at the wrong times. Symptoms of jet lag can include difficulty falling asleep at night, waking up too early, daytime fatigue, digestive changes, and trouble concentrating. 

Anyone who travels long distances by air can experience jet lag, but it tends to be worse in older adults, international travelers who cross several time zones quickly—for example, from Arizona to Australia—and airline crews. 

Beyond shift work sleep disorder and jet lag disorder, other circadian rhythm sleep disorders include:

• Delayed sleep-wake phase disorder: In this disorder, the body clock runs late, causing individuals to fall asleep late and wake late. Delayed sleep-wake phase disorder is common among adolescents.
• Advanced sleep-wake phase disorder: This type of circadian rhythm disorder is the opposite of delayed sleep-wake disorder: individuals become sleepy early in the evening and then find themselves waking very early in the morning.
• Non-24-hour sleep-wake disorder: Often seen in fully blind individuals, this disorder is characterized by the internal clock drifting later each day because the normal light signals that synchronize it aren’t received. In fact, between 50%-70% of totally blind individuals develop this disorder.

What causes circadian rhythm disorders?

Circadian rhythm disorders can be caused by any of the following:

• Irregular sleep schedules: Circadian rhythms function best with regularity, so sleeping and waking at different times each day can confuse your internal clock. When sleep patterns are varied, the release of the sleep hormone melatonin and other circadian-regulated processes become less stable.
• Light exposure at night: Your circadian rhythm depends heavily on a clear contrast between bright days and dark nights, but modern lighting—think phones, computers, LED and fluorescent overhead lights, and televisions—creates biological daytime signals late into the evening. This confuses the body clock by suppressing melatonin, the hormone that signals to your body that it’s time to sleep.
• Night shift work: Many people must stay awake when the body is programmed to sleep, including healthcare workers, emergency responders, and hospitality and service workers. Because their working hours tend to overlap with the normal sleep period, shift work sleep disorder can develop.
• Travel across time zones: When you cross more than two time zones, your internal clock still wants to follow the time zone you came from, causing you to feel sleepy and/or hungry at the wrong times.
• Neurologic or medical conditions: Some brain injuries, neurodegenerative diseases like Alzheimer’s disease or Parkinson’s disease, or vision problems can disrupt the light signals that regulate circadian timing.

While most circadian rhythm disorders are rare, shift work sleep disorder and jet lag disorder are the exceptions. Nearly one-third of people who work night shifts will experience shift work sleep disorder, while anyone flying to a destination with a time difference of more than two hours is likely to experience some degree of jet lag.

The most common circadian rhythm sleep disorder symptoms include: 

• Difficulty falling asleep at a desired bedtime: Feeling fully awake when trying to go to bed at a normal time is likely to occur because your internal clock hasn’t reached its biological night yet.
• Waking up too early: On the other hand, you may wake up much earlier and be unable to fall back asleep because your circadian rhythm has shifted.
• Fatigue and low energy: Because sleep is shortened or happens at the wrong time, you may feel unusually tired during the day and struggle to stay alert at work or school. 
• Digestive discomfort: Because circadian rhythms also influence metabolism and digestion, irregular sleep patterns may lead to gastrointestinal discomfort or changes in appetite.
• Headaches or general malaise: Some people can experience headaches or a general feeling of malaise resulting from severe disruptions to their circadian rhythm.
• Memory and learning: Deep sleep and REM sleep are essential for memory consolidation. So, when sleep occurs at abnormal times or becomes fragmented, the brain has fewer opportunities to process and store information effectively.
• Attention and concentration: People with circadian rhythm disorders often report difficulty focusing, mental fatigue, and slower reaction times. This is because poorly aligned sleep timing reduces alertness and slows cognitive processing. 
• Poor work or school performance: Sleep loss and circadian misalignment can impair executive functions like planning and risk assessment, and daytime sleepiness may reduce your productivity, reaction time, and decision-making ability.
• Mood regulation: Circadian rhythms influence essential hormones like melatonin and cortisol. Consequently, when this 24-hour cycle is disrupted, emotional regulation can suffer, leading to irritability, low mood, or increased stress sensitivity. 

• Mental health vulnerability: Chronic circadian disruption can increase an individual’s likelihood of anxiety, depression, and burnout. Long-term circadian misalignment has also been linked to an increased risk for cognitive decline later in life, and is linked to mood disorders such as bipolar disorder.

Circadian Rhythm Disorder Diagnosis

Unlike many conditions that rely on specific tests or imaging, sleep specialists generally diagnose circadian rhythm disorders by tracking sleep patterns and symptoms over time. 

Your doctor might use the following tests, exams, and tools to diagnose circadian rhythm disorders:

• Physical exam with detailed history: First, your provider will ask about your sleep patterns, work schedules, travel history, and symptoms, as the timing and duration of your symptoms will provide important clues.
• Questionnaires and sleep scales: Standardized questionnaires can help identify patterns and assess your sleep timing preferences, circadian tendencies, and daytime sleepiness. 
• Light exposure and behavioral assessment: Your doctor might also evaluate your daily light exposure, work schedule, screen use, and lifestyle factors to determine if any of these are influencing the timing of your circadian rhythm.
• Sleep diary: Keeping a daily log of sleep and wake times for at least one week, recording when you go to bed, when you fall asleep, any middle-of-the-night awakenings, and when you wake, may aid in diagnosis. This detailed tracking can help your healthcare provider spot patterns that can suggest misalignment.
• Actigraphy: Actigraphy uses a watch-like device worn on the wrist to track your movements and light exposure. It also continuously records your sleep-wake activity for days or weeks to provide an objective view of your circadian rhythm.
• Sleep study: If a different sleep disorder, like obstructive sleep apnea, is suspected, your doctor may prescribe a sleep study to help rule out other causes of circadian rhythm disorder.
• Melatonin timing tests: In some sleep clinics, specialists can measure the timing of melatonin release in your body. The most common method measures your dim-light melatonin onset (DLMO), which indicates when your internal clock signals the start of biological nighttime.

Ultimately, to diagnose a circadian rhythm disorder, a professional will confirm that your sleep timing is consistently misaligned with the required (or desired) schedules; that this misalignment causes insomnia, excessive sleepiness, or impaired functioning; that these symptoms persist for a significant period of time (except for jet lag disorder); and that other sleep or medical conditions do not fully explain the issue you’re experiencing.

The most common treatment options for circadian rhythm disorders include: 

• Light therapy: One of the most effective treatments for circadian rhythm disorder is timed exposure to bright light. This is because light is the strongest signal for resetting the circadian clock—morning light can shift your internal clock earlier. In contrast, evening light can shift it later. 
• Controlled light avoidance: Just as light can reset the clock, avoiding light at the right times can help align your circadian rhythm. Avoidance techniques can involve reducing screen exposure in the evening, wearing blue-light blocking glasses at night, and keeping your sleeping environment dark.
• Melatonin: Melatonin supplements can help shift circadian timing when taken at specific times of day, since melatonin signals to your brain that nighttime is approaching. Doctors often recommend melatonin for jet lag disorder, non-24-hour sleep-wake disorder, and delayed sleep timing. Your sleep physician can help you pick a dosage and timing that works for you.
• Adjustments to sleep hygiene: These include consistent sleep and wake times, regular daytime light exposure, limiting caffeine late in the day, and establishing a stable bedtime routine. Each of these healthy sleep habits can help stabilize a circadian rhythm disorder. 
• Sleep schedule adjustments: Gradually shifting your sleep and wake times over several days until you reach your desired schedule can help retrain your internal clock. 
• Wake-promoting medications: In some cases, sleep medicine specialists prescribe alertness-enhancing medications to help people stay awake during required working hours. For example, Modafinil is sometimes used to treat shift work sleep disorder.

In conditions like Alzheimer’s Disease or Parkinson’s, treating the underlying disease often improves sleep timing.

All things considered, circadian rhythm disorders are highly treatable. When circadian alignment improves, people often see improvements not only in their sleep but also in their mood, cognition, energy levels, and overall mental health.