Week 10: The nap, the coffee and the sweet treat

Week 10, everyone else's crunch, nothing due here. So we spend it on the three things students reach for under stress, and what the evidence says about each. One of them does the opposite of what you think.

10 May 2027

Open the slides

Where. Outdoors, venue posted by the Friday before. Opens with the ten-minute detox.

Nothing more is due in this course during teaching. The only thing left is the log, which you have been keeping as you go and which is not due until after the whole cohort’s exams are finished. That is deliberate, and it is explained on the Assessment page.

What it means for today is that we can spend a whole lecture on the least glamorous question in the course. Namely, what actually helps when you are fried and spiralling in week 10.

The folk answer is a nap, a coffee, or something sweet. One of those is well supported, one is genuinely double-edged in a way that matters specifically in a course about rumination, and one appears to do the opposite of what everyone believes.

The nap, which works#

Rosekind and colleagues (1994) ran the study everyone half-remembers. Pilots on real long-haul transpacific flights, given a 40-minute rest opportunity in the cockpit. They slept about 26 minutes on average and showed clearly better vigilance and physiological alertness than the no-nap group. The benefit was still there through descent and landing, which is the part of a flight where you would like your pilot alert.

A pedantic note in keeping with this course. The famous “34% better performance, 54% better alertness” numbers attached to that study come from the team’s 1995 write-up in the Journal of Sleep Research, not the original NASA memorandum everybody links to. Small thing. We care about it here.

Now the part that actually changes your behaviour. Brooks and Lack (2006, Sleep) tested naps of 5, 10, 20 and 30 minutes in sleep-restricted people.

So the advice is not “have a nap.” It is “have a ten-minute nap,” and the half-hour version can leave you worse off before it leaves you better.

One important distinction the internet blurs constantly. Mednick, Nakayama and Stickgold (2003, Nature Neuroscience) showed a nap can consolidate learning about as well as a night’s sleep. But that needs roughly 60 to 90 minutes, and it is a memory effect, not an alertness one. Two literatures, opposite advice. Ten to twenty minutes if you need to be sharp this afternoon; an hour and a half if you have just learned something and want to keep it, and are willing to feel terrible for the first twenty minutes after waking.

Also worth saying plainly. Nobody has studied naps and rumination. That connection, sleep on the loop and it might close, is this course’s guess, not a finding.

The coffee, which is oversold#

Caffeine blocks adenosine and makes you feel more alert. That much is not in question. What is in question is whether it makes you better than baseline or merely returns you to it.

Peter Rogers and colleagues (2010, Neuropsychopharmacology) tested 379 people after 16 hours without caffeine. Habitual consumers given caffeine came back to baseline alertness, with no net gain. Non-consumers did show a rise, which was offset by increased anxiety and jitteriness. Rogers followed this up in 2014 with a paper defending the position outright. Caffeinated regular consumers never actually exceed the alertness of people who never took it up. This is contested rather than settled, but it is a serious argument, and it reframes your morning coffee as maintenance rather than enhancement.

Then the bit that matters in this course. Caffeine is anxiogenic at dose. In studies giving 400–750 mg to people with panic disorder, around half had a panic attack, against none on placebo. That is a large dose and a clinical population. The honest counterweight arrived recently. Hoppe and colleagues (2025, Journal of Psychopharmacology) gave a realistic 150 mg to panic-disorder patients and controls in a double-blind crossover and found no increase in subjective anxiety, contrary to their own hypothesis.

So at everyday doses, probably fine for most people. At high doses, a real risk. The European Food Safety Authority puts habitual safety at up to 400 mg a day and 200 mg in a single dose, which is roughly two to four cups depending on who made it. And if you are someone whose spirals come with a racing heart, you already know more about this than the literature does.

The coffee nap is real, incidentally. Reyner and Horne (1997, Psychophysiology) gave drivers 200 mg of caffeine plus a nap under 15 minutes and cut driving incidents to 9% of placebo, against 34% for caffeine alone. Replication has been mixed. At least one later study found the combination no better than either on its own, so file it under promising rather than proven.

The sweet treat, which does the opposite#

This is where the folk theory falls over, and it falls over hard.

Mantantzis, Schlaghecken, Sünram-Lea and Maylor (2019, Neuroscience & Biobehavioral Reviews) meta-analysed 176 effect sizes from 31 studies and 1,259 participants, asking whether carbohydrate improves mood. The title is “Sugar rush or sugar crash?” and the answer is neither-then-yes.

• No positive effect on any aspect of mood, at any time point. Not on alertness, not on mood, not at 30 minutes, not at an hour.
• Alertness was lower within 60 minutes of consumption.
• Fatigue was higher within 30 minutes.

The sugar rush does not exist. What exists is a measurable dip, arriving right about when you were counting on the lift.

Before anyone gets smug, this is a claim about sugar, not about treats. If a biscuit and ten minutes away from your desk helps you, the plausible mechanism is the ten minutes, the ritual, and the deliberate stop, not the biscuit. That psychological route is not disproven; it is unstudied, which is a different thing, and it is precisely the sort of confusion this course exists to catch. You had a break and credited the sugar.

What to reach for instead#

Two things with better support than any of the above.

Move. Ensari and colleagues (2015, Depression and Anxiety) meta-analysed single bouts of exercise and found reductions in state anxiety of around a quarter of a standard deviation. Modest, not miraculous, and more than sugar manages.

Take a break that is actually a break. Which brings the whole course back around. Week 5 found that only undemanding activity produces incubation, and week 6 found a phone break measuring like no break at all. A walk works. A scroll does not. The ten-minute nap is arguably the purest empty slot available to you.

One negative result, for honesty’s sake. A well-known 2011 study claiming brief mental breaks restore focus failed to replicate in 2017. It is quoted constantly. We are not quoting it.

Discussion#

• Which of the three do you actually reach for, and what were you crediting it with? Then check that against the table above.
• The treat finding is the clearest case in the course of a felt improvement that measures as the opposite. Where else have you got that wrong?
• If the coffee is maintenance rather than enhancement, is that an argument against starting, or just an argument against expecting much?
• Everyone in this room is under load right now from other courses. What has genuinely helped this week, and can you tell it apart from what merely felt like it did?