Sleep phase disorder: Sleep, circadian rhythms and your energy performance levels.

Tahnee Kinsman BAppSci, IBLS-AIS, PhD Candidate
Sleep Science Editor

What is sleep phase disorder?

Energy levels depend on our circadian rhythm. Psychological function and physical exercise studies have revealed optimal times of performance coincide with the circadian rhythm. A study on sprinters has demonstrated peak running performances occurring at 1pm and 7pm relative to a normal circadian rhythm 1 (Javierre C, et al. 1995).

An internal pacemaker within our brain signals hormones to maintain the circadian rhythm. In order to coincide with our 24 hour clock, the pacemaker requires environmental cues, with light being the most effective. Where people have been deprived of light, their internal circadian rhythm adjusts to a 24.5hour cycle. While this could suggest that the earth was once much larger, or that our species migrated from another planet, it is more believable to be a minor deficiency in our complex human physiology. Regardless of what we believe, the implications of this biological phenomenon can be quite significant over only 10 days of light deprivation.

After 10 days of light deprivation a 30min circadian shift equates to a 5hour phase difference meaning that a person would be eating breakfast when they should be eating lunch. More meaningfully, they would be feeling excessively tired in the mornings when they should be working. This is a common complaint of people with delayed sleep phase disorder.

Are you a candidate for sleep phase disorder?

Cold hands and feet in the evening, excessive morning or afternoon tiredness and difficulty sleeping and are common symptoms of sleep phase disorder. Predicting timing of the circadian rhythm is not simple without a body core temperature measure. The normal circadian rhythm should result in body core temperature being lowest between 3 and 6 in the morning. Sleep onset is assisted by peripheral cooling therefore the temperature of our extremities such as the hands and feet, may be an indicator of our circadian phase. Warm feet begin to cool as sleep onset approaches but even without the onset of sleep, the circadian cooling effect continues.

Thus extremely cold feet at normal sleep time could be indicating an advanced sleep phase disorder since the cooling process begun long before bedtime. Sleep itself is a warming process so without sleep, the body's peripheral temperature may feel cold. Studies have described the death of rats caused by sleep deprivation as similar to the death caused by hypothermia. In delayed sleep phase, the signal for sleep onset being highest body temperature occurs closer to the point where body temperature should be at its lowest. Furthermore, when the signals for sleep onset, ie, the cooling process is delayed, peripheral warming may continue to result in a sensation of even warmer feet.

Both advanced and delayed sleep phase disorders are characterised by difficulty sleeping. The best way to distinguish between the disorders is by the morning wake time. An advanced sleep phase disorder will result in early morning awakening whereas delayed sleep phase disorder sufferers will tend to sleep until an alarm wakes them. Typically, delayed sleep phase sufferers will therefore experience morning tiredness whereas the advanced sleep phase sufferer will be more tired in the afternoon.

Distinguishing characteristics of advanced versus delayed sleep phase disorders (Table 1).

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Symptoms exhibited
Delayed Sleep Phase
Advanced Sleep Phase
Excessive tiredness
Awakening time
Late in the morning
Early hours of morning
Sleep onset discomfort
Hot feet
Cold feet
Sleep difficulty
How to correct your sleep phase?

Light is perhaps the best tool available that we can manipulate to help correct our circadian rhythm. This light can come from both natural sources such as sunlight, but research has shown that synthetic light, such as that radiating from a globe, can also be used.

So for Delayed sleep phase…

Bright light in the early hours of the morning will generally result in phase advance. Often repeated bright light exposure over consecutive mornings will be necessary although it depends on the delay of the sleep phase. It is a good idea to read outside in the early hours of daylight to assist the sleep phase shift. When the eyes focus to read the pupil dilates and more light hits the back of the retina where it can be sensed by the brain. Exercising from late afternoon onwards should be avoided.

And for Advanced sleep phase…

Bright light exposure and exercise in the evening will help delay sleep onset. Taking melatonin before sleep may help prevent early morning awakenings.

A synthetic hormone (chronbiotic) called Melatonin can also be effective for correcting your circadian rhythms. The timing of the ingestion of this supplement is very important, so it's best to take it twenty minutes before the desired sleep onset time. However, melatonin will be less effective if it is taken a long time away from the circadian rhythm sleep time.

Your daytime performance and energy levels can be affected by your circadian rhythm. This is heavily tied in with your sleep habits such as bed times and wake up times. A slight shift progressing over many days can send your body clock out of sync. But luckily there are solutions; light therapy and melatonin are amongst the best. They can help you feel a lot younger by giving you a natural waking experience and allow your energy to be released at the optimal time!

By Tahnee Kinsman

Sleep Researcher and PhD Candidate
Australian Institute of Sport
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1. Influence of Sleep and Meal schedules on performance peaks in competitive sprinters. C. Javierre, M. Calvo, A Diez, et al. Int J. Sports. Med. 17 (1996) 404-408.

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