Does poor sleep hurt your memory?

Lying awake at 3 a.m., it is easy to wonder what the lost hours are doing to your memory. People who report short sleep are somewhat more likely to be diagnosed with dementia years later, but that may be because the disease disturbs sleep first. Insomnia itself can be treated, and if it has gone on for months, it is worth taking to a doctor.

How much sleep do adults need?

The NHS says most adults need 7 to 9 hours a night. Other health bodies draw the line a little differently, so treat it as a range rather than a target to the minute.

What have the long-term studies found?

The Whitehall II study followed nearly 8,000 people for up to 25 years. All of them were in work when they joined, and they were asked how long they slept on a weeknight at 50, 60 and 70. Those who said six hours or less at all three ages had about a 30% higher risk of a later dementia diagnosis than those who said seven hours each time.

Sleeping long is linked with higher risk too. A 2024 review of 31 studies found the link for nine hours or more, whether people were followed for up to ten years or for longer.

Is the short sleep causing it?

Possibly not. In the same review, short sleep (six hours or less) was linked to a 46% higher risk of dementia in studies that followed people for ten years or less. In studies that followed people for longer, the increase was small and could have been chance. The reviewers read that as a sign that short sleep might be an early symptom of dementia rather than a cause of it.

Whitehall II, which asked about sleep from age 50, did find a link over the long run. Like any study that only observes people, though, it can't rule out other explanations.

Does treating poor sleep protect your memory?

Trials have started to test this. One published in June 2026 recruited 200 people with long-term insomnia, average age 69, whose memory and thinking were normal.

Half had cognitive behavioural therapy for insomnia, known as CBT-I: six weekly sessions covering time in bed, relaxation and beliefs about sleep, then monthly calls for 12 months. The other half had stretching and lifestyle education.

The therapy worked on the insomnia, which eased more than in the comparison group. After a year, though, the trial found no clear difference between the groups in memory, in mental speed, or on tasks such as naming the ink colour of printed words and repeating strings of digits. The researchers call it a pilot and say longer follow-up is needed to know whether better sleep changes the risk of dementia.

Is better sleep still worth working on?

Yes. The trial showed that insomnia itself can be treated, even though the effect on thinking is unproven. It also sits alongside moving, eating well and seeing people among the habits health experts link to a healthy brain.

Much of the NHS's advice for insomnia is about everyday habits:

• Get up at the same time every day, and go to bed only when you feel sleepy.
• Relax for at least an hour before bed, with a bath or a book.
• Keep the bedroom dark and quiet; curtains, an eye mask or ear plugs can help.
• Exercise during the day, but not in the four hours before bed.
• Don't smoke or drink alcohol, tea or coffee for at least six hours before bed.

If that isn't enough, the NHS may offer CBT, face to face or through an online programme. Sleeping pills are prescribed only for a few days or weeks at most.

When should you see a doctor?

The NHS suggests booking an appointment if better habits haven't helped, if you've slept badly for months, or if it's making daily life hard to cope with.

It also lists the signs of sleep apnoea, where breathing stops and starts during the night: gasping, snorting or choking sounds, waking a lot, and loud snoring, often with tiredness during the day. If someone has heard you at night, it can help to bring them along, because they have noticed what you can't.

If it's memory that worries you, in yourself or in a parent, the NHS advises against guessing at the cause. It lists sleeping problems among the treatable things that can sometimes lie behind memory problems, alongside stress, anxiety and depression.