What you've heard
Wait 90 minutes after waking before your first coffee
Verdict
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.
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.
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
Sources
- 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.
Educational content, not medical advice. Disclaimer.