Circadian Rhythm and Sleep

Circadian rhythm is a an innate biologic feature of living organisms that relates to time and life functions. Generally, this rhythm is based on a 24-hour period.

Circadian Rhythm Sleep Disorders refer to disruptions in the timing of sleep and wake and the consequences that result form the disruption. We all have an internal clock that regulates certain biological functions over a 24-hour period. That clock is referred to as your circadian rhythm..

As with many body functions, your circadian rhythm can get out of alignment for a variety of reasons. For example, the demands of a job, newborn baby or travel can disrupt your body clock. When your internal rhythm is off, it can affect your sleep as well as your wake time.

What is a Circadian Rhythm?

We all have an internal clock that regulates certain biological functions over a 24-hour period. That clock is referred to as your circadian rhythm. Patterns of hormone production, appetite, and cell regeneration are associated with a person’s circadian rhythm, and circadian rhythm disorders can play a significant role in disrupting your sleep-wake cycle.

People have a circadian rhythm that involves being awake during the daytime and sleeping at night. Certain factors affect your circadian rhythm including melatonin production. Melatonin is a hormone in the body that helps regulate sleep. Melatonin production is affected by sunlight. When you’re exposed to light, melatonin levels are low. But when light decreases, such as in the evening, your body makes more melatonin, which in turn makes you sleepy.

Keep in mind; there are individual variations in a person’s internal clock.  For example, you might feel you are naturally a morning person, or maybe you consider yourself a night owl.

Types of Circadian Rhythm Sleep Disorders

There are several circadian rhythm disorders:

• Jet Lag: Jet lag is probably one of the best known circadian rhythm disorders. Jet lag is caused by changing time zones, which can disrupt light cues and regular bedtimes. In most cases, jet lag is temporary and regular sleep patterns return.
• Sleep Shift Disorder: Shift work disorder involves problems sleeping due to your work schedule. In most cases, it occurs due to working overnight or rotating shifts. What happens is when you work overnight, your body needs to stay awake, which goes against your natural circadian rhythm. The conflict between what your internal clock wants to do and what you are forcing yourself to do disrupts normal sleep.
• Delayed Sleep Phase Syndrome: Delayed sleep phase syndrome involves the inability to fall asleep at what is considered conventional bedtimes. For example, people with delayed sleep phase syndrome may not fall asleep until 2 or 3 am. Since bedtimes are much later than typical, people with the syndrome usually wake up later in the morning. The problem for people with delayed sleep phase syndrome is their sleep pattern may not match their school or work start time, which leads to excessive daytime sleepiness. The cause of delayed sleep phase syndrome is not entirely understood, but it is more common in teens.
• Advanced Sleep Phase Disorder: Advanced sleep phase disorder is the opposite of delayed sleep phase syndrome. It involves problems staying awake during conventional or socially acceptable times. For example, people with advanced sleep phase syndrome may fall asleep at 7-8 pm and wake up very early at 3-4 am. The cause of advanced sleep phase syndrome has not been identified, but it occurs more commonly in the elderly.
• Non-24 Hour Sleep-Wake Disorder: People with Non-24 Hour sleep wake disorder have a sleep-wake cycle that is longer than 24 hours. Their sleep and rise times drift a little later each night. Sleep times continue to change and eventually may go all the way around the clock. The condition is most common in people who are blind. It may occur in blind people due to lack of light and dark patterns to regulate sleep.

Symptoms of Circadian Rhythm Disorders

Symptoms of circadian rhythm disorders may vary in severity. Some people only experience problems, such as jet lag when traveling. In other cases, the disorder may be chronic and affect daily living. Circadian rhythm disorders often cause decreased quality of sleep, which can lead to sleep deprivation.

Symptoms of Circadian Rhythm Disorders may include:

• Problems falling asleep
• Daytime sleepiness
• Headaches
• Difficulty concentrating
• Decreased cognitive performance
• Fatigue

Treatment for Circadian Rhythm Disorders

Treatment for circadian rhythm disorders may vary based on the severity of symptoms and the specific disorder. In most cases, one of the treatment approaches listed below is recommended.

Lifestyle and Behavioral Changes: In some instances, certain behavior and lifestyle changes may be all that is needed to treat a circadian rhythm disorder. Behavioral changes may include avoiding naps, caffeine and nicotine a few hours before bed. Adjusting exposure to light may also help. For example, if you have delayed sleep phase disorder, avoiding light exposure in the evening including light from cell phones and computers may be useful. Maintaining consistent bedtimes even on the weekends can also be helpful.

• Light Therapy: Light therapy may be recommended for certain types of circadian rhythm disorders. Light therapy involves sitting in front of a bright light box for a certain amount of time prescribed by a sleep specialist. The treatment readjusts your body clock and is intended to delay or advance bedtime. The timing of the light therapy is based on the disorder.
• Medications: If other treatments are ineffective, medication may be an option to treat a circadian rhythm disorder. Different classifications of sleep medications may be used, such as benzodiazepines or nonbenzodiazepines, which promote sleep. Melatonin, which helps regulate sleep, may also be beneficial. Certain medications may only be recommended short-term due to the possibility of developing dependency.

More on Normal Circadian Rhythms

 There’s a continuum of chronic types among people with healthy circadian clocks, ranging from ‘morning’ people (larks) who prefer to go to sleep early and awaken early, to ‘evening’ or ‘night’ people (owls), who prefer to go to sleep late at night and awaken late in the morning. Regardless of whether people are larks or owls, those with normal circadian systems can –

• Wake up and go to sleep at the same time every day, if they choose to;

• Fall asleep at night allowing enough sleep time before having to get up, and can awaken in time for whatever they need to do in the morning;

• Start to fall asleep earlier each night and get up earlier than usual within just a few days, if a new routine so requires. Adapting to an earlier sleep/wake time is known as ‘advancing the sleep phase’, and it’s very possible for healthy people to advance their sleep phase by approximately one hour each day.

Interesting Sleep Research on Circadian Rhythms

In one lot of research, volunteers were placed in special apartments or caves for several weeks, with no clocks or other time cues. Interestingly, without time cues, these volunteers went to bed roughly an hour later and awoke roughly an hour later each day. The results of these experiments appeared to show that humans have a free-running circadian rhythm of approximately 25 hours.

However, because these volunteers were able to control artificial lighting and the evening light caused a phase delay, more research was carried out. This new research showed that all adults free-run at an average of just over 24 hours (24 hours and 11 minutes, to be precise!). Our biological clock requires regular environmental time-cues in order to maintain a 24-hour day/night cycle. These time-cues, also known as zeitgebers, include our daily routine, and sunset and sunrise. We need time-cues to keep our normal human circadian clock aligned with the rest of the world.

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