Perhaps you know that person who tries so hard to go to bed "early" but never makes it before 3 am. Or the one who's always up before the rooster, regardless of their bedtime.
Whether you tend to be a "night owl" or an "early bird," every person's body has an internal clock that helps regulate when their bodies feel tired and ready for bed and when they're ready to greet the new day. These internal clocks, called circadian rhythms, are partly regulated by melatonin, the hormone that tells the body it's time for sleep, and by sunlight, which resets our internal clocks.
Being more of a night person or more of an early person is not abnormal. In fact, doctors use the official terms "eveningness" for owls and "morningness" for larks. But it is unusual to be an extremely late night person who is unable to sleep before the wee hours of the morning, or to be someone who is wide awake at 4 am and simply can't keep their eyes open past 8 or 9 pm.
People whose circadian rhythms or internal clocks seem to be way off kilter from the typical day-night cycle might have a sleep phase disorder. This is different from insomnia, which means a person has trouble sleeping regardless of the time of day.
A sleep phase disorder occurs when a person's internal clock is off by at least two hours from what is considered "typical." There are four main sleep phase disorders, which are types of the broader category of circadian rhythm disorders.
They include delayed sleep phase disorder, advanced sleep phase disorder, free-running disorder and irregular sleep-wake rhythm.
Delayed Sleep Phase Disorder
Delayed sleep phase disorder is the most common of these conditions, affecting up to 15 percent of adults, according to the American Sleep Association. The percentage is likely higher among younger adults, and the disorder is especially evident in teenagers. Both men and women experience delayed sleep phase disorder about equally.
A person with delayed sleep phase disorder is unable to fall asleep until very late, though the precise time will vary by person. Someone who tries to go to bed at 10:30 p.m., for example, but can never fall asleep before 1:30 a.m., regardless of what time they woke up or what they did, ate or drank that day, may have delayed sleep phase disorder.
People with delayed sleep phase disorder have difficulty getting up early as well. Even if they do manage to fall asleep by 9 or 10 pm the night before, they might still feel groggy and sleepy getting out of bed any time before noon.
Although a person may have trouble getting to sleep earlier because of caffeine or other stimulants, delayed sleep phase disorder means a person pretty much always has this difficulty. Caffeine and/or sleeping pills may not change the person's clock even if it helps them sleep sooner or be a bit more alert in the morning.
Advanced Sleep Phase Disorder
Advanced sleep phase disorder is the opposite of delayed sleep phase disorder: a person wakes up extremely early, usually before dawn, and also becomes sleepy much earlier in the evening than a typical person would. The range of waking time could be anywhere from 1 to 5 am, and bed time might be anywhere from 6 pm to 9 pm.
Just as the person's sleep time is shifted, their other body functions associated with the circadian rhythm are also shifted "forward." Their bodies release melatonin and other hormones sooner, they tend to eat earlier than usual and their body reaches its peak temperature earlier in the 24-hour cycle.
Advanced sleep phase disorder is more rare than the delayed one, however. It affects about 1 percent of all adults and is more likely to occur among seniors. This disorder tends to interfere with daily life, especially school and work, less often than delayed sleep phase disorder, but it can still be frustrating.
For example, any kind of evening activities might be unenjoyable for people with advanced sleep phase disorder, or they may not be able to attend them at all if they are simply way too sleepy.
Other Circadian Rhythm Disorders
The other two sleep phase disorders are much more uncommon than advanced or delayed disorders: non-24-hour sleep-wake syndrome, (also called free-running disorder) and irregular sleep-wake rhythm. Free-running disorder is quite rare and can be very challenging to treat.
Basically, a person with free-running disorder does not have 24 numbers on their internal clock. Instead of looping every 24 hours, a person with free-running disorder might loop every 25 or 26 hours, so their bedtime and wake time appear to be constantly shifting as the weeks go on.
The most severe type of free-running disorder documented involved a small handful of cases in which people had a 72-hour internal clock: they remained awake for two days and then slept for a full 24 hours. But even the more typical 25- or 26-hour clock version is very rare and primarily affects blind people. In fact, it's estimated that over half of all blind people have this disorder because their brain is unable to receive the typical light cues that help keep the internal clock ticking at the right pace.
With a person's sleeping and waking times pushed back one or two hours every day, it can be extremely difficult to have a typical job or to go to school.
Irregular Sleep Wake Rhythm is also a rare condition in which a person takes multiple "naps" throughout a 24-hour period without ever having a single extended stretch of sleeping night. Instead of having 16 or so hours of waking time and 8 hours or so of sleep, a person with irregular sleep wake rhythm may take four two- to three-hour naps throughout the day and night.
People with irregular sleep wake rhythm still tend to get as much sleep time as a typical person, but they do not usually get as much deep sleep time. Deep sleep is essential for the body to regenerate, so this disorder is the most likely of the four to cause physical health problems, memory difficulties or poor habits such as unhealthy eating.
In addition to the four sleep phase disorders, circadian rhythm interruptions or conditions can result from jet lag, shift work, drug or alcohol effects or a medical condition.
Causes of Sleep Phase Disorders
All the causes of sleep phase disorders are not fully understood, but there are definitely some factors that have been known to worsen circadian rhythm disorders. Certainly, crossing more than two time zones in a single day can contribute to sleep phase difficulties. Also, insomnia can make these disorders worse or prevent treatment from working.
Irregular Sleep Wake Rhythm has been linked to dementia, brain damage and other neurological conditions that might precipitate it.
Most sleep phase disorders tend to have strong genetic components as well. About 40 to 50 percent of people who have a family member with a sleep phase disorder also tend to have one themselves.
There are, however, environmental influences that can worsen the disorder or prevent treatment from working. Ambient light in the evenings is one of the worst culprits.
Regardless of whether it's lamp light, the television, a computer or even your smart phone's light, having exposure to light in the evenings can weaken your body's ability to stay on track. The release of melatonin in your body may be later, and/or your body may not respond as strongly to morning light to reset your clock if you were exposed to light too late the night before.
While most sleep phase conditions are not harmful in and of themselves, not getting enough sleep can be harmful. Insufficient sleep can cause drowsiness that impairs a person's ability to work, drive or function in day-to-day activities.
Extended periods without sufficient sleep have also been linked to various chronic health conditions, including obesity, diabetes and cardiovascular risks such as high blood pressure and stroke.
Even free-running disorder does not cause health problems by itself, though it may lead a person to feel stressed or experience depression if their disorder prevents them from participating in typical day-to-day life. People with free-running disorder still get good-quality sleep and deep sleep while they are asleep.
But if you suspect you have a sleep phase disorder and it is preventing you from getting sufficient sleep because you have to get out of bed at a certain time for work or school, it may be worth seeking treatment for the condition.
There are several options that can be explored to treat sleep phase disorders. First, a doctor will likely want to learn more about your individual schedule, either by asking you to keep a sleep diary or else giving you an overnight sleep study.
There are three broad categories of treatment. These include sleep scheduling, shifting your circadian phase by "resetting your clock" and using hypnotic and/or stimulant medications.
Treatment options to consider include taking melatonin supplements, using bright light therapy, and adjusting your in-bed and waking times gradually in small increments. There is a small amount of evidence that acupuncture may be helpful as well.
William Kohler, MD, the director of the Florida Sleep Institute in Spring Hill, Florida, said that many people find phototherapy lights to be most helpful. These lights run from about $50 to $150 and are available without a doctor's prescription.
"Most people feel that the blue spectrum is the most effective," Dr. Kohler said. "Then's an older method called chronotherapy, in which the person continually phases their sleep time, delaying sleep every 2 hours until they are on track."
But don't expect these treatments to turn you from an owl into a lark or vice versa.
"Like many sleeping disorders there is no cure in a traditional sense, and the disorder must be constantly monitored and effective treatments for the patient actively continued," according to the American Sleep Association
"There is always a risk of relapse into old patterns with most circadian rhythm disorders, so following strict bedtimes and also waking times should be enforced," they state on their website.
"This includes setting an alarm to wake in the morning even on days when waking up at a specific time may not be required. You may also need to completely or severely limit your intake of stimulants and sedatives at all hours," they write.
Dr. Kohler added caution that relapses occur when people don't keep to their new schedules. "If you have a relapse, you should use phototherapy again," he said. He said that teenagers tend to be more susceptible to relapse because they're more sensitive to changes in sleeping schedule.
More information on circadian rhythm disorders is available in an American Academy of Sleep Medicine review published in the journal Sleep in 2007.