Adult Sleep: How Many Hours Of Sleep Does An Adult Need?

Science shows that the need for 8 hours of sleep for an adult is a myth when it comes to optimal health

Optimal adult sleep hours are one of the biggest myths in sleep science.

“You need to get 8 hours of sleep a night”. Just like “brush your teeth in the morning and night” and “don’t wipe your butt with sandpaper”, 8 hours of sleep is common health knowledge everyone’s mum told them. But is it legit? Could the idea that adults need 8 hours of sleep be a myth?

Do you actually need an 8 hour sleep each night? Is 8 hours of sleep ideal?

And if 8 hours of sleep is good, surely 9, 10, 11 or even 25 hours of sleep a night must be even better? Can’t get too much of a good thing right?

Surprisingly, the largest and most comprehensive analysis of sleep duration and health to date says that when it comes to adult sleep hours, the answer to both questions is actually…... 

No.  

The analysis, a systematic review and meta-analysis of 67 studies (from 1673 identified) looked at the dose-response relationship between sleep duration and:

• All‐cause mortality (dying from any means);

• Total cardiovascular disease;

• Coronary heart disease; and

• Stroke in healthy populations.

The studies covered 3.8 million people over time spans ranging from 2.5 years up to 38 years (yup, that’s a lot of people over a long period of time).

How Many Hours Of Sleep Is Required For Adults?

The review found that:

• There was a U shaped relationship between sleep duration and negative health outcomes;

• Both sleeping too short and too long was associated with higher risk of all-cause mortality (read: dying);

• The lowest risk of dying was associated with roughly 7 hours of sleep.

So when it comes to adult sleep hours, 8 hours of sleep is a myth. 

The ideal amount of hours of sleep for an adult is 7 hours. 

This is interesting because when it comes to the question: How many hours of do adults typically sleep the common finding is that the average sleep hours for an adult is also 7 hours. 

So most of us are probably getting enough sleep.

Here’s are some graphs from the study that show the relationship between 7 hours of sleep and optimal health for adults quite nicely (kinda more a J-curve than a U though).

Is Too Much Sleeping Bad For You?

The short answer surprisingly is yes - too much sleeping is bad for you. 

Despite most of us having heard about the dangers of too little sleep (& those dangers are real and include other risks, such as death from accidents), the study’s findings suggest sleeping too much is bad for your health.

Why Is Sleeping Too Much Bad For Your Health?

The study didn’t look specifically at the question “why is sleep too much bad for your health”, but the authors offered a few science-backed clues behind why sleeping too much could be bad for your health:

• Chronic illness that causes long sleep (e.g. obstructive sleep apnea);

• Increased risk of atherosclerosis (hardening of the arteries);

• Increased feelings of fatigue and lethargy, and insufficient restoration against stress and disease;

• Depressive symptoms, low socioeconomic status, unemployment, low household income, low level of education, and other risk factors for mortality and cardiovascular events.

(The actual reason has become clearer since this study, so I’ll blog on why too much sleeping is bad for you in another post).

What’s the takeaway from all this morbid talk?

How Many Hours Of Sleep Is Required For Adults For Good Health?

For most people 7 hours is roughly the ideal amount of sleep if health, not dying etc are important to you….

And when it comes to sleep, both too much sleep and too little sleep is bad for your health. 

The study was published in Journal Of The American Heart Association (Yin, et al, 2017).