24 May How do I know if my body clock is working?
The most important external signal for the biological clock is light. When the eye senses light, it sends signals to the suprachiasmatic nucleus (SCN), a tiny part in our brains. This resets our internal body clock every day. Our body does this to make sure rhythms don’t drift out of line with the environment. Although our rhythms cycle about once every 24 hours, without light and dark (for instance with total blindness) humans actually tick a little more slowly – about 23.1 hours. Thus, if we didn’t have daylight we would get out of synchrony with night and day.
People with Delayed Sleep Phase Syndrome (DSPD) have trouble adjusting and go to bed and wake up late, which can be inconvenient when trying to schedule activities such as work and school. In this neurological sleep disorder the person is unable to fall asleep until the wee hours, typically somewhere between 2 am and 6 am, and sleeps correspondingly longer in the daytime, often well into the afternoon.
How is DSPD diagnosed?
A sleep specialist will generally discuss a patient’s history and complaints. If a circadian rhythm disorder is suspected, the doctor will require a log of when the patient sleeps and wakes. This may be obtained by monitoring sleep-wake patterns using a wrist activity monitor, a device worn like a wristwatch which tracks movement. The sleep history is most useful if it can be obtained when the patient is sleeping on her natural schedule, without attempting to meet the requirements imposed by work or school. Many patients will have already researched circadian disorders, and come prepared with a sleep log.
Often the sleep doctor will order an overnight polysomnogram (sleep study), to detect or to rule out other disorders such as sleep apnoea or PLMD (Periodic Limb Movement Disorder). For people with DSPD, this test should be performed when the patient can sleep normally, which may be later than the lab’s usual schedule allows. Some doctors will ask for a Multiple Sleep Latency Test (MSLT) to be conducted during the patient’s day, to evaluate the possibility of narcolepsy. In some patients, multiple disorders may be present, or another disorder may be the cause of the reported symptoms.
If you think you are suffering from this or any sleep disorder, please contact your GP for more information.
- Sleep Health Foundation https://www.sleephealthfoundation.org.au/fact-sheets-a-z/203-body-clock.html
- Circadian Sleep Disorders Network 2018. Delayed Sleep phase disorder. Questions and answers. Available online: https://www.circadiansleepdisorders.org/docs/DSPS-QandA.php. Last modified Jul 15, 2017.