How much should you sleep: hours or a steady schedule?

"How much should I sleep?" is the question I get most, after the food and the training. Three questions hide inside it: how long, how regular, and which one to protect when both will not fit. Here are the three, with the numbers from the studies.

Short answer: Large reviews put the lowest risk of death and of heart disease for a typical adult near 7 hours a night. Under seven, the risk of death rises by about 6% for each hour you cut. If you train hard, you will often need more than seven. My rule of thumb: once seven hours are in place, a steady bed time and wake time usually pay off more than chasing an eighth hour.

Length: there is a low point, and it is a curve

Sleep follows a curve: risk falls toward a low point and rises again on both sides, and in the Yin 2017 numbers below it rises faster on the long side. Large reviews, hundreds of thousands to millions of people, agree on the lowest risk of death and of heart disease near 7 hours a day. Under seven, the risk of death rises by about 6% for each hour you cut.

The dose-response meta-analysis of Yin 2017 puts it in numbers. Each hour under seven adds about 6% to the risk of death. Each hour over seven adds about 13%. Compounded, that is roughly 12% higher risk at five hours and about 28% at nine, versus seven (my calculation from the per-hour figures).

One reading matters. The extra risk with long sleep is thought to largely reflect hidden illness. There is no good evidence that nine hours harms a healthy person who trains hard. If you regularly need much more than nine hours and still wake up tired, talk to your doctor. What short sleep does to fat loss, specifically, is in sleep and fat loss.

People who train need more

Seven hours is where the lowest risk sits in population data, and adult guidelines recommend at least that. If you train hard, you will often need more, since sleep is when much of the recovery happens. In one small study, 11 college basketball players aimed for 10 hours in bed for several weeks and objectively slept almost 2 extra hours a night. Their sprint got faster, and their free-throw and three-point accuracy each rose by about 9 percentage points. So for an active person the target is what you need to recover, often more than seven hours. Teenagers (13 to 18) are advised 8 to 10 hours, and their body clock runs later.

Short sleep makes a calorie surplus easier

This is the line that matters if you are losing fat. Short sleep pushes intake up, and expenditure does not rise to match it. It is easy to miss. Here is what small lab studies found:

• after two nights of 4 hours in bed (versus 10), 12 healthy young men had about 28% more of the "hunger" hormone ghrelin and about 18% less of the fullness hormone leptin,
• the same men reported a 33 to 45% bigger appetite for sweet, salty and starchy foods,
• in another study (Calvin 2013), people on restricted sleep ate about 559 extra kcal (calories) a day for eight days, and their activity energy expenditure did not rise.

You eat more, and you do not burn it off. In a small two-week study, dieters sleeping 5.5 hours lost less fat and more lean mass than when they slept 8.5 hours, on the same calories. So when "the diet is perfect and it is not moving", check two things: how accurately you track, and how you sleep. Five hours can break an otherwise clean deficit from underneath. Hunger itself is in cravings and hunger. The deficit those extra calories wipe out is in calorie deficit: how much to eat.

If the short or poor sleep does not budge, it can have a medical cause, so talk to your doctor. Loud snoring, pauses in breathing at night, or heavy daytime sleepiness despite enough hours are worth taking to your doctor too.

Regularity: the second lever

Length is half the story. The other half is regularity: how close your bed time and your wake time stay. In wrist-tracker data from 60,000 people, sleep regularity was a stronger marker of lifespan than sleep length. Compared with the least regular fifth of people, the more regular groups had a 20 to 48% lower risk of death, even after accounting for how many hours they slept. Observational studies link so-called social jetlag (a big shift between weekday and weekend times) with higher body weight and worse metabolic markers. A wrecked schedule from night work is the extreme version, in shift work and fat loss.

When you have to choose

In the ideal you have both. Real weeks force a compromise. This order is my rule, built from the findings above.

• Sleeping under 7 hours? Length comes first. The hit to hunger shows up fast, and a steady schedule alone is unlikely to make up for it. Get the hours into the bed first.
• Sleeping 7 hours or more? Regularity wins. Once the length is enough, steady times pay more than chasing an eighth hour at the cost of chaos.
• Always: a fixed wake time, also on weekends, is one of the most practical anchors for your body clock. Within about an hour is a good working target.

In short: first secure seven hours. Once you have them, a steady bed time and wake time usually matter more than the eighth hour.

Frequently asked questions

Is 9 hours of sleep harmful?

In the Yin 2017 meta-analysis, each hour over seven added about 13% to the risk of death. That extra risk is thought to largely reflect hidden illness. There is no good evidence that nine hours harms a healthy person who trains hard. If you regularly need much more than nine hours and still wake up tired, talk to your doctor.

How much sleep does a person who trains need?

Often more than 7 hours, since sleep is when much of the recovery happens. In one small study, college basketball players who objectively added almost 2 hours a night got a faster sprint, and their free-throw and three-point accuracy each rose by about 9 percentage points.

Can short sleep stall fat loss?

It can. In one small lab study, two nights of 4 hours in bed raised ghrelin by about 28% and lowered leptin by about 18%. In another, restricted sleep added about 559 kcal a day while activity energy expenditure did not rise. In a small two-week study, dieters sleeping 5.5 hours lost less fat and more lean mass than at 8.5 hours, on the same calories. If short or poor sleep stays, talk to your doctor.

Which matters more, length or regularity?

My rule of thumb: under 7 hours, length comes first. At 7 hours or more, regularity is usually the better lever. Keep the wake time fixed, including weekends, ideally within about an hour.

Why does a steady bed time matter?

In wrist-tracker data from 60,000 people, regularity was a stronger marker of lifespan than length. Compared with the least regular fifth of people, the more regular groups had a 20 to 48% lower risk of death, even after the hours were accounted for.

Sources, so you can check:

1) Yin J. et al., J Am Heart Assoc 2017 (DOI 10.1161/JAHA.117.005947)

2) Windred DP. et al., Sleep 2024 (DOI 10.1093/sleep/zsad253)

3) Chaput JP. et al., Appl Physiol Nutr Metab 2020 (DOI 10.1139/apnm-2020-0032)

4) Spiegel K. et al., Ann Intern Med 2004 (DOI 10.7326/0003-4819-141-11-200412070-00008)

5) Calvin AD. et al., Chest 2013 (DOI 10.1378/chest.12-2829)

6) Mah CD. et al., Sleep 2011 (DOI 10.5665/SLEEP.1132)

7) Nedeltcheva AV. et al., Ann Intern Med 2010 (DOI 10.7326/0003-4819-153-7-201010050-00006)

8) Paruthi S. et al., J Clin Sleep Med 2016 (DOI 10.5664/jcsm.5866)

Martin Barna

Online nutrition and fitness coach. Since 2013 I have coached 600+ clients. Evidence-based nutrition and training.

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This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.