Sleep medicineMar 27, 2007

Treating the Body’s Internal Clock in Chronic Insomnia

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 31, 2026

Abstract

Circadian rhythms significantly influence sleep patterns, with maximum sleepiness occurring when core body temperature is at its lowest.

Maximum sleepiness coincides with the lowest core body temperature.
Two alertness periods, the wake-maintenance zone and the wake-up zone, flank the time of maximum sleepiness.
An earlier drift of circadian rhythm can lead to premature awakening and early morning awakening insomnia.
Conversely, a delay in the circadian rhythm can cause sleep onset insomnia.
Chronobiologic treatments, such as bright light and melatonin, may effectively target these insomnia types.
Bright light in the morning and melatonin 4-8 hours before bedtime may help adjust circadian rhythms.

Simplified

Circadian rhythms have a strong effect on the ability to sleep across the 24-h period. Maximum sleepiness occurs at the phase of lower endogenous core body temperature. This period is bracketed by two periods of alertness: a "wake-maintenance zone" occurring 6-10h before the time of core temperature minimum, and a "wake-up zone" occurring 4-7h after the minimum. Therefore, if the circadian rhythm drifts earlier with respect to the attempted sleep period, the wake-up zone can impinge on the end of the normal sleep period resulting in premature awakening and the development of early morning awakening insomnia. Similarly, a delay of the circadian rhythm can impose the wake-maintenance zone on the attempted bedtime and lead to sleep onset insomnia. Therefore, these two types of insomnia should be treatable with chronobiologic effects such as bright light and, possibly, melatonin administration. Bright light stimulation at normal wake-up time and melatonin administration 4-8h before normal bedtime can phase advance circadian rhythms to an earlier time. While morning bright light has been efficacious for sleep onset insomnia, evening melatonin administration has yet to be tested. Early morning awakening insomnia has been treated with phase delays imposed by evening bright light but not yet with morning melatonin administration. There is now sufficient evidence to warrant the consideration of chronobiologic manipulations such as bright light therapy for the treatment of chronic sleep onset and early morning awakening insomnia that show evidence of circadian delay or advance, respectively.

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Treating the Body’s Internal Clock in Chronic Insomnia

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