Sleep

How to sleep better – circadian rhythm, sleep pressure, light and caffeine

How do you sleep better? A walk through what Matthew Walker, Andrew Huberman and Bryan Johnson agree on - the circadian rhythm, sleep pressure, light, caffeine and the evening routine.

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What this covers

  1. The circadian rhythm and the body clock
  2. Sleep pressure and adenosine
  3. Melatonin and light
  4. Caffeine and its half-life
  5. Morning light and daylight
  6. An evening routine and winding down
  7. The bedroom - dark, cool and quiet

What this covers (cont.)

  1. Alcohol, nicotine and meals
  2. Sleeping through a Norwegian winter and bright summer nights

The two systems everything else rests on

Nearly every piece of sleep advice you hear works through one of two systems. Grasp which one, and you also understand why the advice is given – and what happens when you break it.

Circadian rhythm and sleep pressure

System 1

The circadian rhythm

  • The body clock that tells you where in the day you are
  • Set first and foremost by light
  • Melatonin belongs here – the signal that evening has come
  • That is why morning light works, and why a fixed wake-up time counts for more than a fixed bedtime

System 2

Sleep pressure

  • How long it is since you last slept
  • Builds through the whole day, as adenosine
  • Reset when you sleep – and partly by a long afternoon nap
  • That is why caffeine works: it gets in the way of the adenosine signal without removing the pressure
The two are independent of each other, and you sleep well when they pull the same way. Lying awake while exhausted is usually sleep pressure running high while the circadian rhythm still thinks it is daytime.

Why the afternoon coffee counts

Caffeine has a half-life of five to six hours. That does not mean the effect is over by then – it means half of it is still there.

One cup of coffee at 3pm

15 19 23 03 The whole cup Bedtime: about a third left
The curve is calculated from a half-life of five and a half hours. It varies a great deal between people – some clear caffeine nearly twice as fast as others – so the figure shows the shape of what happens, not a number that applies to everyone. The point is that the caffeine is not out of your body just because you no longer feel it.

The day that hangs together

Light is the strongest single factor you control yourself, and it works in both directions: plenty of light early helps, plenty of light late hurts.

Melatonin through the evening

15 19 23 03 Dim light Bright light in the evening
Melatonin is not a sedative – it is a signal that night has begun. Bright light through the evening dampens that signal and pushes it later, and sleepiness then arrives later than it otherwise would. The curves show the shape of what happens, not figures that apply to everyone: the timing varies with your own body clock, and the size of the effect varies with how much light actually reaches your eyes.

Four links, in order

  1. 1A fixed wake-up timeThe same hour every day, weekends included. This is the link that holds the rest in place.
  2. 2Light earlyGet outside into daylight as early as you can. In winter even a grey day counts for more than indoor lighting does.
  3. 3A caffeine cut-offSet a limit in the middle of the day and keep it. The difference shows up in the evening.
  4. 4An hour of winding downDimmed light, a lower gear, no screen right before. You do not go from a hundred to zero in a minute.

↻ And then it begins again the next morning

The links act on one another: get up at a fixed time and the morning light is easier to reach, and then the evening falls into place by itself. When one link goes, it is usually the first that has slipped.

Your resting pulse in the hour before bed tells you whether the body has actually wound down.

What keeps it up: hard training late, a large meal, alcohol, nicotine, caffeine, stress and a room that is too warm. If your pulse is noticeably above what is normal for you as you go to bed, the body is still working – and you will sleep worse even though you feel tired. This is one of the few things you can measure yourself, with a watch or a ring, instead of guessing.

Alcohol makes you fall asleep faster, but sleep worse.

Why this confuses people: falling asleep is the part you notice. What happens through the rest of the night – broken sleep and less dream sleep – is the part you are not awake enough to register. That is why it feels as though it works.

Key points

  • Sleep is governed by two systems - the circadian rhythm and sleep pressure. Everything else builds on those.
  • A fixed wake-up time matters more than a fixed bedtime.
  • Caffeine has a half-life of five to six hours, and turns up in more than you think.
  • The body needs about an hour to wind down - you do not go from a hundred to zero.

Key points (cont.)

  • Alcohol makes you fall asleep faster, but sleep worse.
  • The bedroom should be dark, cool and quiet.

Questions this answers

  • How can I sleep better?
  • What is the difference between melatonin and adenosine?
  • How long does caffeine stay in the body?
  • What time of day should I stop drinking coffee?
  • Why does a fixed wake-up time matter more than a fixed bedtime?
  • What do I do the day after a bad night?

Questions this answers (cont.)

  • How cold should the bedroom be?
  • Does alcohol help you sleep?
  • What do I do when I am lying awake and cannot fall asleep?
  • How do I get enough light during a Norwegian winter?

Sources

  • Matthew Walker – Why We Sleep
  • Andrew Huberman – Huberman Lab, the episode on sleep
  • Bryan Johnson – work on sleep and optimisation

Spørretimen

Read the whole thing at

www.sporretimen.no/en/episodes/sovn-laer-noe-nytt/