What you've heard: Wait 90 minutes after waking before your first coffee
Should you wait 90 minutes after waking for coffee?
Untested, and the reasoning looks backward. Drink your coffee when you like it in the morning; the timing that matters is the hours before bed. Evidence grade: Emerging for any benefit of waiting.
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The "What you've heard" box in Chapter 8
Untested, and the reasoning looks backward
Untested, and the reasoning looks backward. Drink your coffee when you like it in the morning; the timing that matters is the hours before bed.
The evidence
The idea borrows real physiology. A brain chemical called adenosine helps build the pressure to sleep; the claim is that it needs time to clear after waking, and that coffee on top of the morning rise in cortisol, a stress hormone, sets up a crash. No trial has compared coffee at waking with coffee 90 minutes later. The mechanism also looks backward: in cats, adenosine rose during waking and fell during sleep, so it should be low after a night's rest, though no one has measured it in people just after waking. And in a controlled trial, after five days of regular caffeine the first morning dose no longer raised cortisol, though a later dose still did: daily use blunts the response rather than removing it.11
Where the book tests it
Related claims
- Is mouth taping safe, and does it work?Unsupported, with a safety catch.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
- Is sunscreen bad for you?Against: the one trial runs the other way.Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
- Do blue light glasses work for sleep?Mostly unsupported; skip the glasses unless a clinician suggests them for a specific sleep problem.Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.
- Does ten minutes of morning sunlight set your body clock?Right direction, invented number.Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
- Do tart cherry juice and magnesium help you sleep?Unproven.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
- Can NSDR or yoga nidra replace lost sleep?A pleasant way to rest, not a substitute for sleep.Evidence grade: Emerging. Early, small, animal-only, or actively contested.
Sources
The "What you've heard" box in Chapter 8
- 11.Porkka-Heiskanen, T., Strecker, R.E., Thakkar, M., Bjorkum, A.A., et al. (1997). "Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness." Science, 276(5316), 1265-1268. https://doi.org/10.1126/science.276.5316.1265 ; Lovallo, W.R., Whitsett, T.L., al'Absi, M., Sung, B.H., et al. (2005). "Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels." Psychosomatic Medicine, 67(5), 734-739. https://doi.org/10.1097/01.psy.0000181270.20036.06 (After five days at 300 or 600 mg a day, a 9 a.m. dose no longer raised cortisol, but a 1 p.m. dose did; the authors conclude that responses are "reduced, but not eliminated" in daily users.) Adenosine data are from the basal forebrain of cats.
Note numbers are those of Chapter 8, Sleep.
This verdict is one of the "What you've heard" boxes in Chapter 8, Sleep, where the book tests the claims people repeat against the studies behind them. The grade rates the evidence behind the verdict, by the book's stated method.
Educational content, not medical advice. Disclaimer.