Non-24-hour Sleep Wake Disorder




Non 24 hour sleep wake disorder refers to a steady pattern of one- to two-hour delays in sleep onset and wake times in people with normal living conditions. This occurs because the period of the person's sleep-wake cycle is longer than 24 hours. The condition most commonly affects people who are blind, due to an impaired sense of light-dark cycles. Non 24 hour sleep wake disorder can also affect sighted people. The cause of the disorder in these cases is incompletely understood, but studies suggest melatonin levels play a role.

Apart from the social stress or depression that living with this disorder may cause, the disorder itself is not considered harmful. The actual quality of sleep, and more importantly deep sleep, is equal or in many cases better, than those without the disorder.


Symptoms reported by patients forced into a 24-hour schedule are similar to those of sleep deprivation and can include:

  • Insomnia 
  • Visual impairment 
  • Anorexia 
  • Incoordination 
  • Memory impairment
  • Mood atacks


Sighted people with non-24 appear to be more rare than blind people with the disorder and the etiology of their circadian disorder is less well understood. At least one case of a sighted person developing non-24 was preceded by head injury; another patient diagnosed with the disorder was later found to have a "large pituitary adenoma that involved the optic chiasma". Thus the problem appears to be neurological. Specifically, it is thought to involve abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus. Several other cases have been preceded by chronotherapy, a prescribed treatment for delayed sleep phase disorder. "Studies in animals suggest that a hypernyctohemeral syndrome could occur as a physiologic aftereffect of lengthening the sleep–wake cycle with chronotherapy". According to the American Academy of SleepMedicine (AASM): "Patients with free-running (FRD) rhythms are thought to reflect a failure of entrainment".

As stated above, the majority of patients with Non-24 are totally blind, and the failure of entrainment is explained by the loss of photic input to the circadian clock. Non-24 is rare among visually impaired patients who retain at least some light perception; even minimal light exposure can synchronize the body clock. A few cases have been described in which patients are subjectively blind, but are normally entrained and have an intact response to the suppressing effects of light on melatonin secretion, indicating preserved neural pathways between the retina and hypothalamus.


There is no information about prevention but studies suggest melatonin levels play a role in regulating sleep. 


The diagnosis is typically made based on a history of persistently delayed sleep onset that follows a non-24-hour pattern. In their large series, Hayakawa reported the average day length was 24.9 ± 0.4 hours (range 24.4–26.5). There may be evidence of "relative coordination" with the sleep schedule becoming more normal as it coincides with the conventional timing for sleep. Most reported cases have documented a non-24-hour sleep schedule with a sleep diary (see below) or actigraphy. In addition to the sleep diary, the timing of melatonin secretion or core body temperature rhythm has been measured in a few patients who were enrolled in research studies, confirming the endogenous generation of the non-24-hour circadian rhythm.

The disorder can be considered very likely in a totally blind person with periodic insomnia and daytime sleepiness, although other causes for these common symptoms need to be ruled out. In the research setting, the diagnosis can be confirmed, and the length of the free-running circadian cycle can be ascertained, by periodic assessment of circadian marker rhythms, such as the core body temperature rhythm, the timing of melatonin secretion, or by analyzing the pattern of the sleep–wake schedule using actigraphy. Most recent research has used serial measurements of melatonin metabolites in urine or melatonin concentrations in saliva. These assays are not currently available for routine clinical use.


Apart from the social stress or depression that living with this disorder may cause, the disorder itself is not considered harmful. Trying to get good quality of sleep plays an important role towards a balanced quality of life.


The first area of treatment will target changes you can make in your routine in an attempt to reset and balance your circadian rhythm. This will include incorporating fixed events into your schedule at set times no matter when you wake up, to try and root your internal clock to a 24 hour rhythm.

Approved therapy
 (Hetlioz) - FDA-approved indication: Treatment of non-24-hour sleep-wake disorder 

Melatonin is also an alternative option to regulate the circardian rythm, However its use and efficacy has not been fully revised by a regulatory agency.

Light treatment for sighted people, chronotherapy and acupuncture have all been used as well with varying results.