For many of us, coffee is the first decision of the day, made before any conscious thought. Alarm, bathroom, coffee. Somewhere in that sequence, caffeine becomes the switch we believe turns the brain on. I have colleagues in Brussels who claim they cannot hold a conversation before the first espresso, and for years I counted myself among them. But is coffee straight after waking really the best use of it? The science is less obvious than the ritual, and the interesting question turns out not to be whether to drink coffee, but when.
The cortisol argument
Cortisol, the hormone that helps regulate our sleep-wake rhythm, rises naturally in the morning. It makes us alert on its own, no caffeine required. This observation led neuroscientist Steven Miller, then at the Uniformed Services University of the Health Sciences in Bethesda, to apply chronopharmacology, the study of how drug effects change across the circadian cycle, to coffee. His reasoning: if cortisol is already doing the job, a caffeine hit on top of the peak delivers less than it could. For people with standard sleep schedules, he suggested a window roughly between 9:30 and 11:30 a.m., when the natural cortisol push starts to fade and caffeine can fill the gap.
Before you set an alarm for 9:29 with the cup in hand, a caveat. There is no universal hour. Cortisol rhythms shift with your wake time and your individual biology, so the honest version of the advice is a principle rather than a schedule: wait a little after getting up, especially if coffee on an empty morning makes you jittery, or if you wake up already wide awake.
The afternoon problem
The other half of the day is better documented, and the news is less forgiving. A study in the Journal of Clinical Sleep Medicine gave participants 400 milligrams of caffeine, about two to three strong cups, at different intervals before bed. Even six hours before bedtime, it measurably cut total sleep time, and participants mostly didn’t notice the damage they were doing to themselves. That doesn’t justify a ban on coffee after 4 p.m. People metabolise caffeine at very different speeds, and plenty of espresso-after-dinner drinkers sleep perfectly well. The more useful move is arithmetic: count back from your usual bedtime, factor in how sensitive you personally are, and let that decide your last coffee of the day.
What the morning pattern study adds
In 2025, a study in the European Heart Journal added a surprising layer. Analysing data from more than 40,000 US adults, researchers found that people who concentrated their coffee in the morning had lower all-round and cardiovascular mortality than non-drinkers. People who spread their coffee across the whole day did not show the same clear advantage.
This is an observational study, so it shows association, not proof that morning coffee extends life. But it fits neatly with everything else: if you’re going to drink coffee, the first part of the day seems to be where it does its best work.
And coffee on an empty stomach?
Here a common belief deserves scaling down. Coffee does stimulate acid secretion in the stomach, but there is insufficient evidence that a cup on an empty stomach causes gastritis or ulcers in healthy people. If you experience heartburn, reflux or a sensitive stomach, having coffee after food rather than before tends to reduce the discomfort. No elaborate breakfast required: just observe how your body responds, which is also the right approach to quantity. The US Food and Drug Administration puts 400 milligrams of caffeine a day, roughly five or six espresso cups, at the level not generally associated with negative effects for most healthy adults, while underlining that sensitivity, metabolism, medications and individual conditions make a real difference.
A strategy, not an hour
So, when should you drink your coffee? Rather than hunting for a magic hour, build a small daily strategy. Keep the first cup out of the first minutes after waking, so your natural cortisol gets a chance to work before caffeine joins it. Concentrate your coffee in the earlier part of the day. Count back from bedtime for the last one. And if your stomach protests, eat something first or move coffee to the end of a meal.
None of this asks you to give up one of the day’s most reliable pleasures. It only asks you to move the hands of the clock a little.
What about you? How many coffees do you drink each day? And when is your favorite time for having a coffee?
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The summary of scientific articles was drafted by a large language model (LLM) and closely edited by me for clarity and accuracy.
