Circadian rhythm sleep disorder

**Circadian rhythm sleep disorders** happen when the circadian rhythm is not working correctly. The circadian rhythm is your body's regulatory system that operates during the 24 hour light/dark cycle. It regulates important bodily functions such as metabolism, body temperature, and hormonal release. The brain structure that is responsible for the circadian cycle is the suprachiasmatic nucleus. When exposed to light, this structure secretes a hormone called cortisol, causing stimulation and arousal. However, when exposed to darkness, the suprachiasmatic nucleus secretes a hormone called melatonin, which is a sleep hormone. When the circadian rhythm is disrupted, there is an increased risk for a variety of health conditions such as cancer, cardiovascular disorders, and metabolic disorders. These are typically labeled as "night owl" or "early bird." Chronotype is typically determined by genetics and fluctuates throughout the lifespan. One chronotype is not better than another, it is simply important to set your internal clock to your chronotype.

## Ways to protect your circadian rhythm function 
* Quantity of sleep
** It is important for adults to get between 7-9 hours of sleep each night.
* Regularity
** It is important to go to bed at the same time each night and wake up at the same time each morning. This allows your circadian rhythm to operate consistently.

* **Shift work syndrome**
Many people have health problems when they work a shift during the times when their circadian rhythms say that they should be asleep. Most people who work later than midnight find it difficult to stay awake. This disorder often occurs to individuals who work the night shift. Shift workers often have difficulty sleeping when they should be sleeping and excessive sleepiness when they are at work. 

## Intrinsic category 
"Intrinsic" means something which happens or comes from within a system or an organism. There are four circadian rhythm sleep disorders of the intrinsic type. Unless they are caused by a head injury, they are usually genetic, that is, people are born with them. They are generally chronic; they do not go away, but they may sometimes be treated.

* **Advanced sleep-phase syndrome**
Advanced sleep-phase syndrome (**ASPS**) is very rare. People with this syndrome are sleepy very early in the evening and they sleep from about 19:00-20:00 in the evening to about 03:00-04:00 in the early morning. Often several people in the same family have ASPS.

* **Delayed sleep-phase syndrome**
Delayed sleep-phase syndrome (**DSPS**) is more common than ASPS and it affects about 0.15% of adults. It usually starts in early childhood or at puberty. Some cases that start at puberty go away when the person is about 20 or 21 years old. DSPS is much more common in teenagers than in adults. DSPS in people older than about 20 usually will have it all their lives, that is, it is chronic.

People with DSPS cannot go to sleep before 03:00-06:00 in the morning, or even later. They cannot wake up in time for school or a job which starts in the morning. They can go to sleep at the same time every night and get up at the same time each day. This means that they are *entrained* (adjusted, synchronized) to the daily light/dark cycle. Even when they try to sleep at "normal" times, they feel most awake late at night.

* **Non-24-hour sleep-wake syndrome**
Non-24-hour sleep-wake syndrome (**Non-24**) is quite rare. People with Non-24 have very unusual sleep timing. Their sleep and wake times are not regulated by daylight; they are not *entrained* (adjusted, synchronized) to the daily light/dark cycle. This is called freerunning sleep.

The worst circadian rhythm sleep disorder in people who can see is Non-24; their "daily" rhythm lasts 25 hours or more so they sleep and wake up one or more hours later each day. Appetite, body temperature rhythm and hormone cycles all keep moving around the clock, coming back to the same time after a few weeks.

About half of totally blind people, who can see no light at all, have Non-24. Their daily rhythm is not exactly 24 hours and it does not adjust to the light/dark cycle in nature because they can not see light. This can often be treated.

* **Irregular sleep-wake disorder**
Irregular sleep-wake disorder is rare, and it is often possible to find out what causes it, for example, a head injury, a mental handicap, dementia or some other sicknesses. People with this disorder sleep and wake several times a day, but not at the same times every day. They sleep about 8 hours a day but never 8 hours together.

## Treatment 
Treatment for these disorders often does not work well. In addition, it can be difficult to find a doctor who knows much about circadian rhythms, as the field of study is quite new.

* **Bright light**
Treatment with bright light is also called phototherapy or light therapy. People with ASPS need a lot of light in the evening and they should avoid bright light in the morning. People with DSPS need bright light as soon as they wake up and should try to avoid bright light before bedtime.

* **Melatonin**
Melatonin is a hormone produced in the pineal gland in the brain. It is normally only produced in the evening and at night. People with ASPS can take melatonin by mouth in the morning. People with DSPS can take melatonin in the afternoon or evening, and this treatment works also for some people with Non-24.

One can buy melatonin in the shops in the USA and Canada. In most other countries one must get it from a doctor or it might not be legal at all.

## Sleep hygiene 
Melatonin is produced in response to darkness and if you are in contact with a bright light before bed it impairs melatonin production.

* It is important to dim the lights at night and refrain from using devices near bedtime.
* Use blackout curtains or a sleep mask to minimize light during sleep.
* When you wake up expose yourself to 10 minutes of natural sunlight. This sunlight exposure triggers cortisol release and helps you feel awake and alert. 
* Bedroom temperature should be around 67 degrees Fahrenheit for optimal sleep.

## References