Non-24-hour sleep-wake disorder (N24SWD) occurs when your sleep-wake cycle gradually shifts out of sync with the 24-hour day. It affects about half of blind people, but it can also affect those with typical vision.

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N24SWD is a circadian rhythm sleep disorder characterized by a disrupted sleep-wake cycle that doesn’t align with the 24-hour day. People with N24SWD often experience a delay in their sleep onset time each day, leading to a progressive shift in their sleep schedule.

N24SWD primarily occurs in blind people, affecting up to half — especially those with no light perception. It can also occur in sighted individuals, though this is relatively rare.

Let’s take a deeper look at the symptoms, risk factors, and treatment options.

N24SWD is characterized by a recurring pattern of sleep-wake cycles that aren’t aligned with the typical 24-hour day. This can lead to symptoms like:

  • difficulty falling asleep at a conventional bedtime
  • excessive daytime sleepiness
  • difficulty maintaining a regular sleep schedule
  • frequent awakenings during the night
  • insomnia or hypersomnia
  • mood disturbances
  • impaired social functioning due to the irregular sleep-wake pattern
  • shifting sleep-wake cycle, where your sleep-wake cycle gradually shifts later each day

N24SWD occurs when your internal body clock runs slightly longer than 24 hours, causing a mismatch with the external light-dark cycle that regulates the body’s circadian rhythm.

This condition occurs in about 50% of blind people, as the lack of light perception makes it difficult for their internal clock to sync with the 24-hour day.

In sighted people, the causes of N24SWD aren’t fully understood, but they may include:

  • having a body clock that runs slightly longer than 24 hours
  • having an unusual sensitivity to light
  • having overexposure to light in the evening
  • having an evening chronotype, or naturally preferring later sleep times
  • experiencing a traumatic brain injury (TBI)

Risk factors for N24SWD include:

  • Blindness: Blind people without light perception are at higher risk.
  • Visual impairment: People with limited or no light perception may also be at risk, though less commonly than those who are blind.
  • Sex: Among sighted people, N24SWD is most common among young males.
  • Mental health conditions: Studies have found that up to 28% of sighted people with N24SWD have a mental health condition.
  • TBI: Some studies have shown that after a TBI, people may experience changes in melatonin levels, which can be linked to sleep and circadian disorders. These changes can happen directly through cellular signals or indirectly through inflammation.
  • Staying up late for many years: Some people may develop N24SWD as a side effect of long-term late-night activities and excessive nighttime exposure to light.
  • Genetics: Researchers have linked specific genes related to the body’s internal clock, known as clock genes, to some circadian rhythm sleep-wake disorders. However, regarding N24SWD, the genetic factors aren’t well understood because there are no clear familial patterns. Further research is still needed.

The International Classification of Sleep Disorders classifies N24SWD as a circadian rhythm sleep-wake disorder.

Diagnosing N24SWD involves assessing your sleep patterns over an extended period. This is typically done using sleep diaries and actigraphy, which is a method of monitoring rest and activity cycles.

The diagnosis is based on a consistent pattern of sleep-wake cycles that are significantly longer or shorter than 24 hours, leading to disruptions in your daily routine and functioning.

N24SWD can be challenging to diagnose, and diagnosis may be delayed, as doctors are often unfamiliar with the condition. They may also mistake it for other sleep disorders or psychiatric conditions. So, a thorough evaluation by a sleep specialist is often necessary to confirm the diagnosis.

The treatment options for N24SWD aim to regulate the sleep-wake cycle and improve overall quality of life. Here are some common treatment examples:

  • Light therapy: Exposure to bright light at specific times can help reset the body’s internal clock. Light therapy is most effective when timed appropriately, typically in the morning to trigger the sleep-wake cycle or in the evening to delay it.
  • Melatonin therapy: Melatonin is a hormone that helps regulate sleep-wake cycles. Taking melatonin supplements in the evening can help synchronize the body’s internal clock with the external environment.
  • Chronotherapy: This involves gradually adjusting bedtime and wake-up times to align with a 24-hour schedule. This method requires careful monitoring and guidance from a healthcare professional.
  • Sleep hygiene: Practicing good sleep habits — such as going to bed at the same time every night, avoiding stimulants like caffeine close to bedtime, and creating a relaxing bedtime routine — may help improve sleep quality.
  • Medications: In some cases, doctors may prescribe medications like tasimelteon, a melatonin receptor agonist with Food and Drug Administration approval, to help regulate the sleep-wake cycle. However, there are potential side effects — like nightmares, strange dreams, and headaches — that may limit people’s use of medications.
  • Behavioral therapy: Cognitive behavioral therapy for insomnia can be effective in treating sleep disorders by addressing negative thoughts and behaviors that contribute to poor sleep.
  • Regular exercise: Regular physical activity can reduce sleep disorders and promote better sleep. But it’s important to avoid vigorous exercise close to bedtime, as this may have the opposite effect.

N24SWD is a circadian rhythm sleep disorder in which people have difficulty synchronizing their internal body clock to the 24-hour day, leading to a daily delay in their sleep-wake pattern.

The disorder is more common in blind people, but it can also occur in sighted individuals — especially those with a history of delayed sleep-wake patterns.

Treatment typically involves a combination of timed bright light exposure and melatonin to help change the sleep-wake schedule.