It was predicted from free running and ultradian cycle studies that sleep-onset insomniacs would have endogenous circadian rhythms that were phase delayed compared to good sleepers.
Thirteen sleep-onset insomniacs and nine good sleepers were selected to differ only in their sleep-onset latencies as confirmed by polysomnography.
their rectal temperatures were measured over a 26-hour constant routine and analyzed with best-fit Fourier curves including 24-h fundamental and 12-h harmonic components.
The temperature rhythm markers of the insomniacs' rhythms were approximately 2.5 h later than the respective phases of the good sleepers.
The usual bedtimes of the insomniacs fell within the "wake maintenance zone" of their delayed temperature rhythm. The good sleepers had typical bedtimes several hours after their "wake maintenance zone" and closer to their body temperature minimum.
It was suggested that manipulations to phase advance the insomniacs' rhythms would reduce their sleep-onset latencies.
It was also predicted that early morning insomnia results from phase advanced circadian rhythms and that sleep maintenance insomnia results from an abnormal phase relationship between the 24-hour temperature rhythm and 12-hour sleep-alert rhythm.
A Good Night's Sleep
“Finish each day before you begin the next, and interpose a solid wall of sleep between the two.”
Ralph Waldo Emerson said these words of wisdom way before science proved the many reasons why a sleep is so critical to our health.
During deep sleep phase, the brain's waste removal system is 10 times more active than during wakefulness, literally restoring the mind for the day ahead. While it's taking out the trash, so to speak, the body works to repair brain cells, reinforce new memories, and even learn new motor skills. Logging enough hours between the sheets each night also does wonders for helping our bodies relieve stress, fight inflammation, maintain healthy body fat levels and ultimately live longer.
Despite the irrefutable evidence of why we should all be getting more shut-eye, nearly half of Americans get less than the recommended amount of sleep each night. When life gets busy, sleep tends to fall to the bottom of our priority lists, leaving our minds and bodies stressed, sick and burned-out.
But that's starting to change: more and more successful people are acknowledging that pretty much any goal is easier to accomplish after a good night's rest.
It has been suggested that two types of insomnia, sleep onset insomnia and early morning awakening insomnia, may be caused by delays and advances respectively of circadian rhythms.
Evidence supports the circadian rhythm phase delay of sleep onset insomniacs.
The present study investigated the phase timing of circadian rhythms of early morning awakening insomniacs compared with a group of age matched good sleepers.
A 24-hr bed rest laboratory session was used to evaluate the endogenous core body temperature and urinary melatonin rhythms. This way lifestyle differences are excluded.
Objective and subjective sleepiness were also measured every 30 min across the session with 10 min multiple sleep latency tests and Stanford Sleepiness Scale.
Maximum and minimum phases of each individual's rhythm were identified using two-component cosine curve fitting.
Compared with the good sleepers, the insomniacs had significant phase advances of 2-4 hours for the temperature and melatonin rhythms. However, the advances of the sleepiness rhythms were not significant.
This latter unexpected result was explained on the basis of variability of sleepiness measures. It was suggested that early morning awakening insomnia arises from phase advanced circadian rhythms which evoke early arousal's from sleep.
Very interesting finding.