Published sleep research · Read this before you chase another hour
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"I slept eight hours and I still feel wrecked."
Say that sentence out loud, because this is the complaint almost nobody has an answer to.
You know your own version. Lying awake for an hour while the day replays itself. Waking at three and not dropping off again. Waking to the alarm with the feeling that nothing happened in between. Falling asleep in front of the television and then lying wide awake in bed. Needing twenty minutes and something warm before you are capable of anything. Sleeping through and still keeling over at three in the afternoon. Reading the same paragraph twice at your desk.
I am Jesse van der Velde. Not a guru and not a doctor. I study and share what published research says about how a body ages. I have been testing that on myself and with the people I guide for more than fourteen years.
The thought I hear a lot of people say is "then I must need more hours".
Because the published work says that hours are one of several things, and probably not yours.
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Ask someone about their sleep and you get a number back. Six. Seven and a half. Eight if things go well.
That is what your phone reports, what the articles argue about, and the first thing your GP asks.
One number is easy to compare and easy to sell. It is also the one thing about sleep you cannot solve with a decision.
And so the complaint you actually have has nowhere to go. Because "I was in bed for eight hours and woke up wrecked" is not about hours at all.
In 2014 Daniel Buysse published an article in Sleep.¹
What was studied: whether sleep health can be defined as something positive and measurable, rather than only as the absence of a sleep problem.
How: this is a concept article and not a trial. Buysse lays out the data showing that several dimensions of sleep are related to health outcomes and that you can measure them both by self-report and objectively, and then gives one proposed definition plus a description of example questions, as an illustration of how it could be done.
The findings, in the form this article actually takes: sleep is not one number. It holds several dimensions, namely how satisfied you are with your sleep, how alert you are during the day, when you sleep, how efficiently you sleep once you are in bed, and how long. Each of those is associated with health outcomes, and each of those can be measured.
Read that list again. Only the last one is the number you always report.
So two people who both say seven hours can have two completely different nights, and the difference sits in the four dimensions nobody asked about.
Now what happens when duration really is the problem, because that has been measured precisely.
In 2003 Hans Van Dongen, Greg Maislin, Janet Mullington and David Dinges published a laboratory experiment in Sleep.²
What was studied: whether human sleep can be shortened over a long period without consequences.
How: 48 healthy adults aged 21 to 38, under continuous behavioural, physiological and medical monitoring. They were assigned by lot to 4, 6 or 8 hours in bed per night, and kept there for 14 nights in a row. A second experiment kept people fully awake for 3 nights. Both had 3 days of measurement beforehand and 3 recovery days afterwards. No other sleep was allowed.
The findings: restricting sleep to 4 or 6 hours for 14 nights produced a loss of performance on every task, and that loss kept piling up day after day, in proportion to how much sleep was missing. Going back to 6 hours or less for a long stretch gave a loss of performance equal to as much as 2 nights of no sleep at all.
And then the finding that changes what you do with this. What the participants reported themselves about their sleepiness responded on the first day and barely moved after that. Their scores drew no real distinction between the 6-hour group and the 4-hour group. The authors write that the participants were largely unaware of the loss that kept piling up.
So after day one your own sense of how tired you are stopped tracking your real state. That is the reason to measure this instead of going by feel.
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14 nights, and the loss never levelled off. That is the laboratory experiment above, in 48 healthy adults under continuous monitoring.² A small, tightly controlled study, with its own limit: nights in a laboratory are not your nights.
15.84 hours. From the same experiment: the statistical model found that the loss of alertness was almost directly proportional to how many waking hours someone had built up beyond that 15.84 hours, with a standard error of 0.73 hours, and that held regardless of how the sleep was lost.²
1,382,999 people, and both sides of the curve. In 2010, Francesco Cappuccio, Lanfranco D'Elia, Pasquale Strazzullo and Michelle Miller published a meta-analysis in Sleep. They pooled 16 studies that together gave 27 separate cohorts, 1,382,999 participants, followed for 4 to 25 years, with 112,566 deaths. Short sleep was linked to a greater chance of dying during the follow-up, a relative risk of 1.12 (95 per cent confidence interval 1.06 to 1.18). Long sleep was linked to it too, and more strongly: 1.30 (1.22 to 1.38).³
Read that twice, because this is the caveat that belongs to this whole subject. Both sides. This is observational work, the authors themselves report clear differences between the studies they pooled, and it does not say that more hours is better. It says the curve has two sides.
You know your own version of this. Mine is a week when I was in bed at half past ten every evening, slept through, and every morning felt as if the night had been cancelled.
For years I read that as a discipline problem. Go to bed earlier. Get up at the same time. Try harder.
Look at what was actually going on. The number was fine. Four other dimensions were never asked about, and my own sense of how tired I was had stopped being reliable.¹ ²
A judgement about your character gets you nowhere. Nothing constructive comes out of it. You cannot try harder to be a different person.
A week you have never measured does have a next step. You can put it next to the published research.
1. Going to bed earlier to get those eight hours.
Whether you go to bed earlier is of course up to you, and for a lot of people it is exactly right.
But be clear about what chasing a number does and does not do. It gets you more time in bed. It says nothing about the other four dimensions, and that meta-analysis above is the reason nobody may promise you that more is better: both short and long habitual sleep were related to a greater chance of dying during the follow-up, and on the long side that relation was larger.³
2. Looking at the number on a tracker.
What it does: report a duration every night. What it does not do: tell you which of the five dimensions is troubling you, or what you can do about it.
And it comes at a second price. That article about defining sleep health exists precisely because the field itself kept describing sleep as the absence of a problem instead of as something with measurable parts.¹
3. "I've got used to six hours."
This is exactly the belief the 2003 experiment was built on, and it did not hold up. On 6 hours a night, for 14 nights, performance kept dropping, while what people reported themselves about their sleepiness levelled off after the first day and drew no distinction between 6 hours and 4 hours.²
You were not imagining that you were doing fine. It is just that your own assessment no longer kept up with what was really happening.
4. Waiting for a quieter month.
What it does: put the question off. What it does not do: change anything about any one of those five dimensions, and that quieter month has a habit of arriving late.
Four moves, one shared problem: none of them starts with what is actually going on with you.
The advice failed here, and it was the sensible sounding kind. You did nothing wrong. It can be different.
This is the heart of it. If sleep consists of several dimensions, then "how many hours did you sleep" is one question out of the five, and the one whose answer you already know.
The question becomes: which of the others is mine?
How long you take to fall asleep. How often you wake and cannot drop off again. How often you wake up rested. How satisfied you are with your sleep as a whole. And how much it gets in the way of your day.
Those five are the sleep scan, and they were not invented here. They are derived from a published instrument.
In 2001 Célyne Bastien, Annie Vallières and Charles Morin published its validation in Sleep Medicine.⁴
What was studied: whether a short self-report questionnaire, the Insomnia Severity Index, reliably measures how severe people find their own sleep problems.
How: two studies. In the first, 145 people being assessed at a sleep clinic filled in the questionnaire, and their answers were compared with a sleep diary. In the second, 78 older participants in a randomised study filled it in several times, and their change scores were compared with sleep diaries and with polysomnography, the measurement in the sleep laboratory. The patient's own version was also compared with versions filled in by clinicians and by people close to them.
The findings: the questionnaire held up statistically, matched the diary measurements, was sensitive to change over time, and the patient, clinician and close-relative versions lay close to one another.
And then the honest limit, said out loud here and not hidden. The published instrument has seven questions. The BioProfile sleep scan takes over only part of it and adds a question of its own, so the published severity bands do not carry over to it. Your score is a profile of your own answers. Never a clinical category, and this page will never tell you that you have something.
What it does do is show you which of those five speaks loudest in your week, and that is exactly what a number on a phone does not give you.
On one condition. That analysis has to be about you: your nights, your mornings, your own answers, question by question alongside what published research describes. A general list of sleep tips does not tell you which of those five is yours.
BioProfile has built that first step. A scientifically validated questionnaire, five minutes, free and with no account.
You answer questions about your nights and about your days. Then you see which signals in your profile speak loudest, and what the research says about them.
Not a medical examination. An analysis of your own answers. You use the outcome yourself, or you put it on the table with your doctor or your coach.
There is nothing to buy at the end. Not on this subject. I have nothing to sell you here. What there is, is your own five answers, read properly for the first time.
You do the free check. Five minutes, no account, and there is nothing to buy.
Even if you do nothing with it, you have traded "then I must need more hours" for an analysis of your own answers. That trade is worth five minutes.
And the next time someone asks how many hours you slept, you will know which of those five is really in play for you.
Do it now, while this page is still open. Tonight is coming either way.
Our scientifically validated questionnaire gives you answers
The scan is not a medical examination. It is an analysis of your own answers. If complaints persist, consult your doctor.
