Six Hours Isn’t Enough

Hi friend,

Before you read any further, answer two questions honestly.

How many hours did you sleep last night? And on a scale of one to ten, how sharp do you feel right now?

If the first answer was six or less and the second was a seven or an eight, this letter is for you, because one of those two numbers is almost certainly wrong, and it isn’t the first one.

In the early 2000s, a team at the University of Pennsylvania led by Hans Van Dongen and David Dinges brought 48 healthy adults between 21 and 38 into a sleep laboratory and kept them there. Each was assigned a nightly ration of time in bed, eight hours, six hours or four, and held to it for fourteen nights straight. A fourth group was kept awake for three days with no sleep at all, so the researchers had something to compare against.

Every two hours while they were awake, the participants sat a battery of tests: reaction time, working memory, mental arithmetic under time pressure. And every two hours they were also asked a simpler question. How sleepy do you feel?

The eight-hour group held steady for the full two weeks. The six-hour group did not. Their performance slipped a little more each day, with no sign of levelling off, and by the end of the fortnight the researchers concluded that six hours or less a night had produced deficits equivalent to up to two full nights without sleep.

That alone would be worth knowing. The second finding is the reason I wanted to write about it.

When the researchers looked at how sleepy the six-hour group said they felt, the ratings rose sharply in the first few days and then flattened. As their performance kept falling, their sense of their own condition stopped tracking it. By the end they reported feeling only slightly sleepy. The authors put it plainly in the paper: the participants were largely unaware of their growing deficits.

So the man on six hours does not feel like a man who has been awake for two days. He feels mostly fine, a little tired, and he is not. The number you gave for how sharp you feel is the measurement this study showed you cannot trust.

That is the cost. A study at Stanford shows the other side of the ledger.

In 2011, Cheri Mah at the Stanford Sleep Disorders Clinic worked with eleven players from Stanford’s men’s varsity basketball team, average age nineteen. For two to four weeks they slept as they normally did, between six and nine hours, while she measured them after every practice: a timed sprint of 282 feet, ten free throws, fifteen three-point shots.

Then she asked them to spend at least ten hours in bed every night for five to seven weeks. Nobody changed their training. Most of them never reached ten hours of actual sleep, landing nearer eight and a half, but that was enough.

Their sprint time dropped from 16.2 seconds to 15.5. Free throws went from 7.9 out of ten to 8.8, a nine percent improvement. Three-pointers went from 10.2 out of fifteen to 11.6. Their reaction times got faster, and they reported feeling better in practices and games.

The study was small and had no control group, so treat the exact numbers with some caution. But these were already elite athletes training at a high level, and the only thing anyone changed was how long they stayed in bed. Mah’s own reading was that they had been carrying a sleep debt the whole time without knowing it, performing below their ceiling and calling it normal.

Put the two studies together and you have the uncomfortable picture. Cutting sleep makes you measurably worse, you lose the ability to notice how much worse, and paying the debt back brings gains large enough to show up on a basketball court.

I used to think of sleep as the one resource I could always borrow from when the week got heavy. The research says the loan is real and the interest is charged to everything else you do the next day.

This is also a question of discipline, not comfort. Getting up at five to work is easy to admire. Going to bed at ten when your phone and your friends are still awake takes more of the same thing, and almost nobody praises you for it.

Here is a two-week test. Fourteen nights, the same length as the Pennsylvania study.

Pick one number you care about. Your main lift in the gym, the hours of focused work you get done before lunch, the time it takes you to write a page. Something you can measure the same way every day.

Week one: change nothing. Sleep as you normally do, write down the hours, and record your number every day.

Week two: add an hour at the start of the night. Keep your wake-up time fixed, the same every day including weekends, and go to bed sixty minutes earlier. Leave the phone outside the room so the hour goes to sleep and not to scrolling.

Compare the two weeks on the number, not on how you feel. Your feeling is the instrument that Van Dongen showed breaks first.

If the number doesn’t move, you have lost nothing but a few evenings of scrolling. If it does, you have found the cheapest performance gain available to you, and you have been leaving it on the table every night.

Until next time
Lorenc - Founder of Success Skill