Non-24 simply means a person’s Circadian Rhythm is not on a 24-hour day. In Sighted Non-24, the Circadian Rhythm is disrupted. Most Non-24 patients are blind, but sighted people can have it, too. In blind people, the lack of light perception throws the Circadian Rhythm out of sync. In Sighted people, there is no singular cause and many factors can be at play.
The primary sign is a sleep–wake cycle longer than 24 hours, usually averaging a 25-26 hour cycle. In someone who is forcing their sleep with alarms, this may look like cyclical insomnia. When your Circadian Rhythm is not aligned with your schedule, you would have insomnia, but when it is, you would sleep fine.
In Sighted Non-24 patients, the retina may not react naturally to light. People with sighted Non-24 can be subjectively sensitive to light (photophobia), or they can be under-sensitive to bright light. Those of us with Sighted Non-24 sleep well and have an average habitual sleep duration of nine to ten hours, but we cannot sleep at the same time every day. This leads to a forward shift.
Sighted Non-24 is not well studied by researchers yet, but we know of several causes.
- It may be a neurological disorder with an abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus.
It could be due to the retina being too sensitive or not sensitive enough to light signals.
- Sometimes, Delayed Sleep Phase Disorder can develop into Non-24. This is often due to chronotherapy. Chronotheraphy is a “treatment” proscribed by patients with DSPD to try and slowly readjust their sleeping habits. Doctors ask patients to force their sleep to a cycle their Circadian Rhythm is not used to and this can create an elongated Circadian Rhythm leading to Non-24.
- A pituitary adenoma can cause Non-24. This is a small benign tumor that disrupts the typical flow of chemicals that control hormones, particularly those related to sleep like melatonin.
- There may also be genetic factors at play. Researchers are currently studying the genetic involvement that may be present in Sighted Non-24. Dr. Alina Patke and her associates at The Rockefeller University are among those studying how genetics are involved in Circadian Rhythms.
- There are likely other unknown causes. We hope raising awareness will inspire researchers to continue searching.
Usually, patients are diagnosed by filling out a sleep log and showing it to a sleep specialist who is literate in Non-24. Non-24-hour sleep–wake disorder is diagnosed when the patient fails to follow (entrain to) a 24-hour light-dark cycle and typical wake times.
This graph is an example of a Non-24 sleep pattern with a semi-predictable forward shift. The date is horizontal and the sleep time is vertical. It shows a semi-predictable pattern and then shows the patient forcing themselves to stay awake on 2/25; then, the pattern tries to correct itself to the patient’s abnormal (Non-24) circadian rhythm.
Treatment for Sighted Non-24 will depend on the cause. For many patients, they find improved health if they sleep whenever they are sleepy, (this is called free-running).
Sometimes, strict light and/or dark therapy can help those with Sighted Non-24 hold on to a 24-hour day. Low dose melatonin under doctor supervision has also been known to help. The pharmaceutical company, Vanda, developed a drug called Hetlioz (tasimelteon) for blind Non-24 patients. It has been known to be effective for some Sighted Non-24 patients, but usually requires patients appeal to their insurance company because it is not approved for Sighted Non-24 and is expensive at around $60,000 per year without insurance coverage.
However, patients may not find improvement with any of these known treatments.
Free-running sleep is a sleep pattern that is not adjusted (entrained) to the 24-hour cycle in nature nor to any artificial cycle. Free-running sleep means that a person with Non-24 chooses to sleep when sleepy and to awaken spontaneously (specifically without an alarm clock or reference to the time of day.
For many with sighted Non-24, sleeping on a normal schedule may be difficult or impossible and trying to do so results in sleep deprivation and elevated stress levels… with all the harmful health effects that accompany sleep deprivation. Sighted Non-24 patients often find they can be much more productive and happier living on the rotating schedule to which their body naturally adheres to. For people with severe cases of Non-24, free-running may be the only realistic option.