Everyone has heard “get eight hours”. Some people swear they’re fine on six.
Others need nine just to feel human.
So how much sleep do you really need? The research gives a clearer answer than you might expect.
For most adults, it’s at least 7 hours a night. And the data hint at something surprising: much more than that isn’t a bonus either.
- US sleep experts say adults should sleep 7 or more hours a night, on a regular basis.
- In a review of 67 published studies and about 3.6 million people, the lowest risk of death was at about 7 hours a day.
- Both less and much more sleep were linked to higher risk, but long sleep may be a warning sign, not the cause.
How much sleep do I need?
If you’re an adult, aim for at least 7 hours a night, most nights.
That’s the joint advice of the American Academy of Sleep Medicine and the Sleep Research Society. In their words: “Adults should sleep 7 or more hours per night on a regular basis to promote optimal health.”
They add that regularly sleeping less than 7 hours is linked to weight gain, diabetes and high blood pressure. It’s also linked to heart disease, stroke, depression and a higher risk of death.
Children and teens need more. Older adults need about the same as younger adults, but the upper limit is lower.
Here’s the US Centers for Disease Control and Prevention (CDC) guide, by age:
| Age | Sleep needed each day |
|---|---|
| 0–3 months | 14–17 hours |
| 4–12 months | 12–16 hours, including naps |
| 1–2 years | 11–14 hours, including naps |
| 3–5 years | 10–13 hours, including naps |
| 6–12 years | 9–12 hours |
| 13–17 years | 8–10 hours |
| 18–60 years | 7 or more hours |
| 61–64 years | 7–9 hours |
| 65 and older | 7–8 hours |
So “eight hours” is a fair rule of thumb, but it isn’t magic. Seven is the floor for most adults.
What the research shows
The sweet spot is about 7 hours
The biggest study behind that answer is a 2017 review in the Journal of the American Heart Association.
The researchers pooled 67 articles from long-term studies. Together, they followed 3,582,016 people for between 2.3 and 34 years.
They compared how long people said they slept with their later risk of death, heart disease and stroke.
The pattern was a U-shaped curve. The lowest risk of death was at about 7 hours a day.
Risk rose on both sides, gently at first and then faster at the long end.
| Hours of sleep a day | Risk of death vs 7 hours |
|---|---|
| 4 hours | 8% higher |
| 5 hours | 4% higher |
| 6 hours | 1% higher |
| 7 hours | Lowest risk (comparison) |
| 8 hours | 4% higher |
| 9 hours | 15% higher |
| 10 hours | 32% higher |
The same curve showed up for heart disease and stroke. For stroke, the lowest risk was at about 6 to 7 hours.
Each hour away from 7 adds up
The researchers also worked out the change per hour.
Below 7 hours, each hour less sleep was linked to a 6% higher risk of death. Above 7 hours, each extra hour was linked to a 13% higher risk.
| Outcome | Each hour under 7 | Each hour over 7 |
|---|---|---|
| Death from any cause | 6% higher risk | 13% higher risk |
| Heart and blood vessel disease | 6% higher risk | 12% higher risk |
| Coronary heart disease | 7% higher risk | 5% higher risk |
| Stroke | 5% higher risk | 18% higher risk |
The results were similar for men and women. The study was funded by Chinese government science programmes, and the authors declared no conflicts.
Why long sleep looks risky, and why I’m cautious about it
The long-sleep numbers look scary. A 10-hour sleeper had a 32% higher risk of death than a 7-hour sleeper.
But the authors themselves call the reasons “more speculative”. Long sleep often comes with poor health.
Long sleep often goes with sleep apnoea, depression, low income or hidden illness. Those same things raise the risk of death.
One detail in the study supports this. Long sleep was linked to dying from heart disease, but not to developing it in the first place.
That pattern fits long sleep being a sign of illness more than a cause of it.
The sleep experts agree. They say sleeping more than 9 hours may be right for young adults, people catching up on lost sleep and people who are ill.
Most adults do best on at least 7 hours a night. Regularly getting less is linked to real health risks. Regularly needing much more than 9 hours is worth mentioning to a doctor.
The newest research
Short sleep in midlife and dementia
A 2021 study in Nature Communications followed 7,959 British civil servants for about 25 years. Over that time, 521 of them developed dementia.
People who slept 6 hours or less at age 50 had a 22% higher risk of dementia than those who slept 7 hours. At age 60, the gap was 37%.
People who slept 6 hours or less at 50, 60 and 70 had a 30% higher risk than steady 7-hour sleepers.
A smaller group wore a wrist device that measured sleep. The results pointed the same way, so this wasn’t only about people guessing their hours.
The authors note that most participants were healthier than average. It’s also a link, not proof that short sleep causes dementia.
Regular timing may matter as much as hours
A 2024 study in the journal Sleep used wrist trackers on 60,977 UK Biobank volunteers. That came to more than 10 million hours of data.
It measured how regular people’s sleep was: going to bed and waking at similar times each day.
Compared with the least regular sleepers, the more regular groups had a 20% to 48% lower risk of death.
The authors found that regularity predicted death risk better than sleep duration did. It’s another observational finding, but a useful nudge.
What earlier research found
An earlier review found the same curve
A 2016 review in Scientific Reports pooled 35 articles, covering 1,526,609 people.
Compared with 7 hours of nighttime sleep, the risk of death was 7% higher at 4 hours. It was 21% higher at 9 hours and 37% higher at 10 hours.
The links held in people without heart disease or cancer at the start. The authors concluded that 7 hours a day should be recommended.
What the sleep experts weighed
The 2015 expert consensus statement also links short sleep to everyday harm.
It says sleeping under 7 hours is linked to weaker immune function, more pain, worse performance, more errors and a greater risk of accidents.
If you nap to catch up
Naps are a common fix for a short night. We looked at whether napping is good for you, and why the length of the nap matters.
How it fits together
Two big reviews, years apart, found the same curve: lowest risk at about 7 hours. Newer studies with wrist trackers point the same way.
How much should you trust this?
Promising. The “at least 7 hours” advice is solid. The exact risk numbers are links, not proof.
What makes it convincing
- Millions of people, followed for years, show the same U-shaped pattern.
- Two separate reviews landed on about 7 hours.
- Wrist-tracker studies confirmed findings based on self-reported sleep.
- Sleep experts, weighing the wider evidence, set the same 7-hour floor.
What makes me cautious
- Nearly all the long-term studies asked people to guess their own sleep.
- Long sleep is often a symptom of illness, which can make it look harmful.
- No trial has assigned people to different sleep hours for years.
- Sleep quality and conditions like sleep apnoea weren’t measured in the main review.
| The evidence shows | The evidence does not show |
|---|---|
| Lowest risk at about 7 hours a day for adults | That 7 hours is right for every single person |
| Regular short sleep is linked to higher risks | That one bad night harms your long-term health |
| Very long sleep is linked to higher risk of death | That sleeping longer causes that risk |
| Regular sleep timing is linked to lower risk | Exactly how regular you need to be |
What this means for you
- Aim for 7 to 9 hours. Seven is the floor for most adults, according to the AASM and the CDC.
- Keep a steady schedule. The NHLBI advises going to bed and waking up at the same time every day. Keep weekends within about an hour.
- Notice big changes. If you regularly need much more than 9 hours, or still feel tired after a full night, talk to a doctor.
- Don’t panic about one bad night. The risks in these studies come from years of habits.
The NHLBI guide to healthy sleep habits has more practical tips.
Poor sleep and low mood often go together. If you’re in crisis, please contact a person, not a chatbot.
In the US, call or text 988. In the UK and Ireland, you can call Samaritans on 116 123, any time.
Elsewhere, Find a Helpline lists free services. If someone is in immediate danger, call emergency services.
In this short video, Mayo Clinic looks at sleep and heart health:
What we still don’t know
- Does long sleep cause harm? Or is it only a sign of illness? The studies can’t tell yet.
- How much does each person differ? Some people may genuinely need less or more.
- Can catching up on weekends undo short weeknights? The evidence is unclear.
- Which matters more, hours or regularity? The 2024 tracker study suggests regularity, but it needs repeating.
- Would sleeping more lower risk for short sleepers? No long-term trial has tested it.
My take: seven is the floor, not the goal
What I like about this research is how consistent it is. Different studies, different decades, the same answer: about 7 hours.
I’m less convinced by headlines warning that sleeping 9 or 10 hours will kill you. The evidence points to long sleep as a signal, not a threat.
So my reading is simple. Protect at least 7 hours, keep your timing steady, and treat a sudden need for much more sleep as information worth sharing with a doctor.
Last reviewed: 2026-10-13
Covers: How much sleep adults and children need, the link between sleep hours and risk of death and heart disease, short sleep and dementia, sleep regularity
Evidence: Promising — expert guidance and large reviews agree on about 7 hours; the health links are observational
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