Last updated: October 2026
Poor sleep is linked with a higher risk of dementia, but it hasn’t been proven to cause it. A large UK study found people sleeping six hours or less at 50 and 60 were more likely to develop dementia, yet dementia itself changes sleep, often years early. Sleep apnoea has the strongest evidence. Worried about your memory? See your GP.
Below: what the research really shows, why sleep may matter for the brain (and what is still unproven), sleep changes that can be an early sign, sleep apnoea, deep sleep, how much sleep to aim for, sleeping a lot, sleep in someone who already has dementia, and when to see a GP.
A calm word first: one bad night, or even a bad few months, does not mean you are heading for dementia. Most sleep problems have everyday causes, and many are treatable. If you or someone close to you has new memory problems or a big change in sleep, the right next step is a chat with your GP.
Does lack of sleep cause dementia? What the research shows
The honest answer is: we don’t know yet. Alzheimer’s Society says there is some evidence that a lack of sleep may increase a person’s risk of dementia, but not enough to say for sure.
The best-known UK evidence comes from the Whitehall II study of London civil servants. Researchers followed 7,959 people for around 25 years, and 521 developed dementia. Compared with people who slept about 7 hours a night:
- sleeping 6 hours or less at age 50 was linked with a 22% higher risk of dementia later on
- sleeping 6 hours or less at age 60 was linked with a 37% higher risk
- people who slept 6 hours or less at 50, 60 and 70 had around a 30% higher risk than people who consistently slept about 7 hours
That last link held even after allowing for things like smoking, heart health and mental health. It is an important finding, but it is still an association: it shows short sleepers were more likely to develop dementia, not that short sleep caused it.
It’s also worth knowing what the biggest review of dementia prevention says. The 2024 Lancet Commission named 14 risk factors that together may account for around 45% of dementia cases: low education, hearing loss, high blood pressure, smoking, obesity, depression, physical inactivity, diabetes, too much alcohol, head injury, air pollution, social isolation, high LDL cholesterol and untreated vision loss. Sleep is not on the list. A 2026 review of 13 earlier reviews pointed out this gap and found a U-shaped pattern, where both short and long sleep were linked with cognitive decline, but rated most of the evidence as low certainty.
For a wider view of what too little sleep does day to day, see sleep deprivation and sleep debt.
Why sleep may matter for the brain (and what’s unproven)
Scientists have a plausible idea of why sleep could matter, often called the brain’s “cleaning cycle”.
- In mice: a 2013 study found the spaces between brain cells widened by about 60% during sleep, letting fluid flow through and clear waste faster, including beta-amyloid, the protein that clumps in Alzheimer’s disease. This is sometimes called the glymphatic system.
- In people: a small 2018 brain-scan study of 20 healthy adults found beta-amyloid rose in parts of the brain involved in memory after just one night without sleep.
What this does not show is that poor sleep leads to dementia in real life. Mouse findings don’t always apply to people, and a short-term rise in a protein after one sleepless night is not the same as a disease that develops over decades. Alzheimer’s Society notes that amyloid may also disrupt sleep, so the two could feed into each other.
Chicken or egg: dementia changes sleep too
The diseases that cause dementia start damaging the brain many years before memory problems show. Some of that damage affects the areas that control sleep and the body clock. So a person’s sleep can change because dementia is already developing, rather than the other way round. Researchers call this reverse causation.
A Dutch study of 2,218 older adults tested this by looking at different gaps between measuring sleep and diagnosing dementia:
- Sleeping 9 hours or more was only linked with dementia over a short gap of about 3 years, which the authors put down to reverse causation.
- Sleeping 6 hours or less, broken sleep and waking too early were linked with dementia most strongly when the gap was 15 years or more.
That pattern fits the idea that long sleep can be an early sign of changes already underway, while short, broken sleep in midlife might be a genuine risk factor. Alzheimer’s Society sums it up well: the relationship may be circular.
Sleep changes that can be an early sign of dementia
Most changes in sleep are not dementia. Stress, menopause, pain, needing the loo at night, low mood, alcohol and some medicines are far more common causes. But some patterns are worth mentioning to a GP, especially if they are new and come with signs of cognitive decline.
| Sleep change | Why it can matter | Read more |
|---|---|---|
| Acting out dreams: shouting, punching or kicking in sleep | Called REM sleep behaviour disorder. Alzheimer’s Society says it may be a very early indicator of dementia with Lewy bodies and Parkinson’s, particularly in older men | REM sleep |
| Sleeping much more than before, or long daytime naps | Long sleep and more napping in later life are linked with dementia in studies, likely as an early sign | Oversleeping |
| Awake at night, dozing in the day | A muddled sleep-wake cycle is common in Alzheimer’s disease | Circadian rhythm |
| Loud snoring, gasping or pauses in breathing | Possible sleep apnoea, which is treatable and linked with cognitive problems | Sleep apnoea |
The NHS lists the common early signs of cognitive decline as memory loss, difficulty concentrating, finding familiar daily tasks hard, struggling to follow a conversation or find the right word, being confused about time and place, and mood changes. If sleep changes come alongside these, book a GP appointment. Ordinary sleep talking on its own isn’t a warning sign; see sleep talking.
Sleep apnoea and dementia
Of all sleep problems, obstructive sleep apnoea has the strongest evidence of a link with dementia risk, according to Alzheimer’s Society. In sleep apnoea, the airway narrows during sleep, so breathing stops and starts and oxygen levels can drop.
A 2017 review of 14 studies found that people with sleep-disordered breathing were 26% more likely to develop cognitive impairment in the six long-term studies. The effect on thinking was small, and the review found no link with memory scores in the shorter studies. Whether treating sleep apnoea lowers dementia risk is not yet known.
Signs to look out for, from the NHS:
- breathing that stops and starts while you sleep
- gasping, snorting or choking noises
- loud snoring and waking up a lot
- feeling very tired in the day, finding it hard to concentrate, mood swings, or a headache on waking
It is more likely if you live with obesity, have a large neck, are getting older, drink alcohol, smoke, sleep on your back or have family members with it. A bed partner is often the first to notice, so take them with you to the GP if you can.
The good news is that sleep apnoea is treatable. Many people use a CPAP machine, which is free on the NHS if you need one, and lifestyle changes such as losing weight and cutting down on alcohol can help. Untreated, it raises the risk of high blood pressure, stroke and accidents caused by tiredness. See our full guide to sleep apnoea and how to stop snoring.
Deep sleep and dementia
Deep sleep (slow-wave sleep) is the stage linked most closely with the brain’s overnight clear-out. We naturally get less of it as we age.
A US study of 346 people over 60 had them do two overnight sleep studies about five years apart, then followed them for 17 years. Deep sleep fell with age, and each percentage point of deep sleep lost per year was linked with a 27% higher risk of dementia. Only 52 people developed dementia, so the numbers are small, and people with a genetic risk of Alzheimer’s lost deep sleep faster, which again raises the chicken-or-egg question.
No one has shown yet that boosting deep sleep protects the brain. What you can do is give yourself the best chance of good-quality sleep: see how to get more deep sleep.
How much sleep to reduce dementia risk?
There’s no proven “dementia-safe” amount. The NHS says adults need 7 to 9 hours, and Alzheimer’s Society gives the same figure. In the Whitehall II study, about 7 hours was the comparison point, and the higher risk showed up at 6 hours or less.
A sensible aim is:
- around 7 to 9 hours a night, at roughly the same times each day
- getting checked if you’re regularly sleeping 6 hours or less and can’t fix it, as long-term insomnia is treatable
- mentioning it to a GP if you’ve started needing far more sleep than you used to
Everyone’s need is a little different. Our sleep calculator can help you work out a bedtime that fits.
Sleeping a lot and dementia
“Is sleeping a lot a sign of dementia?” is one of the most searched questions on this topic. Long sleep is linked with dementia, but it is more likely to be an early signal than a cause.
- In the US Framingham study of 2,457 people (average age 72), sleeping more than 9 hours a night was linked with twice the risk of dementia over 10 years. The link was driven mainly by people who already had mild memory problems, and moving from normal to long sleep over time was a stronger signal. The authors suggest long sleep may be a marker of early brain changes.
- A study of 1,401 older adults who wore activity trackers for up to 14 years found longer and more frequent daytime naps were linked with a higher risk of Alzheimer’s dementia. It worked both ways: more napping came before worse thinking, and worse thinking came before more napping.
Sleeping more has plenty of other causes too, such as low mood, an underactive thyroid, sleep apnoea, medicines and recovering from illness. See oversleeping and how long a nap should be.
For someone who already has dementia, Alzheimer’s Society says it is common to spend a lot of time sleeping, especially in the later stages.
Sleep problems in someone who has dementia
If you care for someone with dementia, broken nights may be part of daily life. Alzheimer’s Society explains that the brain changes in dementia can affect how much, and how well, a person sleeps. They may sleep more in the day, struggle to get to sleep, wake in the night, and not feel rested. Over time, poor sleep may make other symptoms worse.
Some people become distressed, agitated or confused in the late afternoon or evening, sometimes with hallucinations. This is often called sundowning. Possible triggers include:
- tiredness, hunger, pain or needing the toilet
- not enough daylight during the day
- a noisy or busy day
- damage to the body clock from the condition itself
- hearing or sight loss, anxiety or low mood
- side effects of medicines
Practical things that can help: closing curtains once it gets dark to cut confusing shadows, checking for an unmet need such as pain or the toilet, and gently distracting with a favourite topic. Alzheimer’s Society also notes that some dementia medicines, such as donepezil, rivastigmine and galantamine, can cause sleeplessness as a side effect. Never stop or change a medicine yourself; ask the GP or pharmacist whether the timing could be adjusted.
Caring through broken nights is exhausting. Alzheimer’s Society’s support line and local carers’ services are there for you too.
Sleep habits worth keeping at any age
Nobody can promise that better sleep will prevent dementia. But the NHS is clear that what is good for your heart is good for your brain, and good sleep supports both. Habits recommended by the NHS and Alzheimer’s Society include:
- Keep regular times for going to bed and getting up, even at weekends. See how to fix your sleep schedule.
- Get daylight in the morning and stay active in the day, but avoid exercise in the 4 hours before bed.
- Cut caffeine and alcohol at least 6 hours before bed. See alcohol and sleep.
- Make the bedroom dark, quiet and cool, and keep clocks and phones out of sight.
- Put screens down about an hour before bed and build a calm wind-down. See our 60-minute bedtime routine and sleep hygiene tips.
- Don’t lie in after a bad night; keep to your usual wake time.
- Keep moving: regular walking supports heart and brain health. See how many steps a day.
If you wake in the small hours and can’t drop off again, see middle insomnia.
A warm, caffeine-free drink can be a simple signal that the day is over. Our Magnesium Glycinate Sleep Complex is a berry-flavoured bedtime drink with magnesium bisglycinate and citrate, L-theanine and chamomile. Magnesium contributes to a reduction of tiredness and fatigue and to normal psychological function. It isn’t a treatment for sleep disorders or memory problems, and nothing in it has been shown to lower dementia risk. Check with your GP or pharmacist first if you take regular medicines.
Sleeping pills and older adults
The NHS says GPs now rarely prescribe sleeping pills for insomnia, because they can have serious side effects and you can become dependent on them. When they are used, it is for a few days or weeks at most. Alzheimer’s Society adds that most sleeping tablets can cause dizziness and a higher risk of falls, which makes them less safe for people with dementia.
You may have read that some sleeping pills, such as benzodiazepines, are linked with dementia. Alzheimer’s Society says the evidence is mixed, and some research it funded found these drugs did not increase dementia risk. The NHS also warns that sleeping pills can make sleep apnoea worse.
If you already take a sleeping tablet, don’t stop suddenly. Talk to your GP or pharmacist about whether it is still right for you. For long-term insomnia, the NHS says you may be offered cognitive behavioural therapy (CBT), face-to-face or through an online programme. See insomnia and, for melatonin rules in the UK, melatonin in the UK.
When to see a GP
See a GP if:
- you or someone close to you has new or worsening memory problems, confusion or trouble finding words
- you snore loudly, gasp or stop breathing in your sleep, or always feel very tired in the day
- you act out dreams by shouting, kicking or punching
- you have had trouble sleeping for weeks and it affects your daytime life
- you suddenly need far more sleep than you used to
Dementia is not a natural part of ageing, and the NHS says it’s best to talk to a GP sooner rather than later. If you can, take someone who knows you well. The GP will check for other causes of memory problems, which may be treatable, before any referral to a specialist or memory clinic. Feeling foggy rather than forgetful? See brain fog.
FAQs
Does lack of sleep cause dementia?
It hasn’t been proven. Regularly sleeping 6 hours or less in midlife is linked with a higher risk of dementia in a large UK study, but dementia also disrupts sleep years before diagnosis, so cause and effect are hard to separate. Alzheimer’s Society says there isn’t enough evidence to say for sure.
Can sleep apnoea cause dementia?
Sleep apnoea is the sleep disorder with the strongest evidence of a link with dementia risk. A review of long-term studies found people with sleep-disordered breathing were 26% more likely to develop cognitive impairment. It is treatable, so see a GP if you have the signs.
Does CPAP help with dementia?
CPAP treats sleep apnoea and can improve sleep and daytime tiredness. Whether it lowers dementia risk or slows memory decline is not yet known, and more research is needed.
Does lack of deep sleep cause dementia?
Losing deep sleep with age is linked with a higher risk of dementia in one US study, but that doesn’t prove it causes it. Deep sleep naturally falls as we get older, and early brain changes may reduce it too.
Is sleeping a lot a sign of dementia?
It can be one early sign, especially when it is a new change, but it has many other causes, such as low mood, thyroid problems, sleep apnoea and medicines. If you or a relative suddenly need much more sleep, mention it to a GP.
How much sleep do you need to reduce dementia risk?
There’s no proven amount. The NHS says adults need 7 to 9 hours. In the Whitehall II study, the higher dementia risk appeared in people sleeping 6 hours or less, compared with about 7 hours.
Does dementia affect sleep?
Yes. People with dementia often sleep more in the day and less at night, wake often, and may become agitated in the late afternoon or evening, which is known as sundowning. In the later stages, sleeping a lot is common.
Sources
- NHS. Symptoms of dementia.
- NHS. Can dementia be prevented?
- NHS. Sleep apnoea.
- NHS. Insomnia.
- NHS Every Mind Matters. How to fall asleep faster and sleep better.
- Alzheimer’s Society. Sleep and the risk of dementia.
- Alzheimer’s Society. How does dementia affect sleep?
- Alzheimer’s Society. Sleep problems and treatments for people with dementia.
- Alzheimer’s Society. Sundowning and dementia.
- Sabia S et al (2021). Association of sleep duration in middle and old age with incidence of dementia. Nature Communications.
- Livingston G et al (2024). Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. The Lancet.
- Harbishettar V et al (2026). Duration and quality of sleep as risk factors for cognitive impairment: an umbrella review of systematic reviews. International Journal of Geriatric Psychiatry.
- Alders P et al (2025). The effect of sleep disturbances on the incidence of dementia for varying lag times. Journal of Prevention of Alzheimer’s Disease.
- Leng Y et al (2017). Association of sleep-disordered breathing with cognitive function and risk of cognitive impairment: a systematic review and meta-analysis. JAMA Neurology.
- Himali JJ et al (2023). Association between slow-wave sleep loss and incident dementia. JAMA Neurology.
- Westwood AJ et al (2017). Prolonged sleep duration as a marker of early neurodegeneration predicting incident dementia. Neurology.
- Li P et al (2023). Daytime napping and Alzheimer’s dementia: a potential bidirectional relationship. Alzheimer’s and Dementia.
- Xie L et al (2013). Sleep drives metabolite clearance from the adult brain. Science.
- Shokri-Kojori E et al (2018). β-Amyloid accumulation in the human brain after one night of sleep deprivation. PNAS.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex, which is a food supplement and is not intended to prevent or treat dementia or any sleep disorder.
