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Glossary

Circadian rhythm

Defined in topic 23

The roughly 24-hour cycle kept by a self-winding genetic loop found in tissues throughout the body. In dim, controlled conditions the human clock's period averages 24.18 hours.

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Where this comes from

In the reference topic that owns this term

Reference topic 23, Sleep and the Dark You Have Lost, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.

Mismatch card

What it expects

A bright day, a dark night, a falling evening temperature, and the same schedule tomorrow.

What it gets

Days under 100 lux indoors, evenings at 30 to 300 lux, a lit bedroom, a schedule that moves at weekends.

What happens in the gap

Sleep moves later and grows irregular, the melatonin night shortens, and peripheral clocks fall out of step.

The full card, and the topic behind it

What that chapter recommends

3 of the 5 graded recommendations in Reference topic 23, strongest evidence first. How the grades work.

  1. For insomnia, start with what works

    StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

    The American College of Physicians recommends cognitive behavioral therapy as the first treatment for chronic insomnia. Melatonin is not recommended for it in adults.

    Read it in full

  2. Get outside early

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Daylight in the first hours after waking, and at least 250 melanopic lux at the eye through the day (light weighted for its effect on melanopsin). Morning light advances the clock and evening light delays it.

    Read it in full

  3. Dim the last three hours, and sleep in the dark

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Below about 10 melanopic lux in the evening and 1 in the bedroom. Sensitivity varies fiftyfold, so judge by your own sleep. If you get up at night, use a dim night light rather than risk a fall.

    Read it in full

Related terms

The argument behind this term, its studies and its notes are in Reference topic 23 of the reference library. The book gives the practical version. Get the book.