In non-24 hour sleep-wake disorder, previously called free running circadian rhythm sleep disorder, the body’s natural rhythm does not align with a 24-hour daily cycle. For most people, the circadian rhythm responds to light exposure, mealtimes, and social cues with a regular 24-hour pattern of sleep and wake cycles. Other biological patterns like temperature fluctuations and hormone levels also rise and fall according to this 24-hour cycle.
In people with non-24 hour sleep-wake disorder, the body’s circadian rhythm extends beyond 24 hours. Instead of a 24-hour daily cycle, their daily cycle contains 25-28 hours. This results in delayed sleep periods and wake times that gradually get later and later, creating problems with work, school, socializing, and daily responsibilities. In rare cases, the body’s daily cycle is shorter than 24 hours, resulting in progressively earlier sleep times and wake cycles.
These disordered sleep cycles create chronic sleep deprivation, insomnia, fatigue, grogginess, and fragmented or non-refreshing sleep. When people with non-24 hour sleep disorder are allowed to sleep according to their body’s natural cycle, they may find relief from fatigue. For some people, however, fatigue persists even when sleep occurs regularly and for adequate periods of time.
Symptoms of Non-24 Hour Sleep-Wake Disorder
People with non-24 hour sleep-wake disorder often experience:
Difficulty falling asleep at bedtime
Bedtimes that become progressively later
Waking later and later in the morning
Difficulty achieving and maintaining restful sleep
Like several other circadian rhythm sleep-wake disorders, non-24 hour sleep-wake disorder is more common in blind individuals: Between 55 and 70 percent of completely blind people have this condition. Non-24 hour sleep-wake disorder also occurs in an unknown number of sighted people, most commonly those with a history of delayed circadian patterns; in other words, people who may call themselves “night owls” and prefer very late bedtimes.
What Causes Non-24 Hour Sleep-Wake Disorder?
Non-24 hour sleep-wake disorder is a neurological condition caused by abnormalities in the suprachiasmatic nucleus, the region of the brain governing the body’s master clock. For most people, external cues—primarily light exposure—help the body regulate its 24-hour cycle. When the body’s cycle strays from the 24-hour pattern, these cues help bring the circadian rhythm back into alignment. In this way, the body maintains its 24-cycle, despite natural interruptions that might occur from travel, illness, bouts of insomnia, or seasonal changes in light exposure.
In people with blindness, the body cannot use light exposure to help maintain a 24-hour daily cycle. When the circadian rhythm drifts off-course, blind individuals may not be able to re-establish a 24-hour daily cycle without medical help.
Sighted people also experience non-24 hour sleep-wake disorder. In sighted individuals, the disorder is caused by abnormal responses to light exposure, abnormal levels of natural hormones like melatonin, or isolation from natural light or social cues.
Doctors use a patient’s medical history, self-reported symptoms, and sleep diaries to diagnose non-24 hour sleep-wake disorder. A physician may use actigraphy to monitor sleep-wake cycles. In some cases, levels of melatonin may be evaluated with lab tests to determine how hormones rise and fall over the course of a day.
Like other circadian rhythm sleep-wake disorders, non-24 hour sleep-wake disorder is treated with timed melatonin and light therapy. In sighted individuals, these treatments can often successfully shift the circadian pattern back to 24 hours. However, continued treatment and the maintenance of consistent sleep and wake times are essential for long-term symptom control. When these treatments are discontinued, a delayed circadian pattern usually returns. In people with blindness, timed melatonin therapy is the most common, most effective treatment for non-24 hour sleep-wake disorder.