Does Lack of Sleep Cause Dementia?

Very few people care about sleep as much as they should.

We’re told that sleep deprivation is a sign of strength. We get up early (first for school, then for work, then out of habit) and stay up late (to socialise). Spending money on cars and streaming subscriptions and alcohol is ‘normal’ – but healthy food and quality sleep surfaces are viewed as ‘luxuries’.

We have a culture of sleeplessness. That’s a problem, because sleep is the single-most important thing you can do for your health. It affects everything from our mood to our weight to our risk of heart disease.

Frighteningly, lack of sleep is also strongly linked to dementia. Cognitive degeneration is one of Australia’s most widespread chronic health challenges – you probably know someone living with it. It affects one in 12 people over 65 and is our second leading cause of death (after heart disease).

This article will explain how the sleep–brain relationship works, how lack of sleep leads to dementia, and what you can do to keep your brain healthy as you age.

How Sleep Supports Brain Health

No-one knows exactly why we sleep. One theory is that sleep lets our bodies repair our cells [1]. Some scientists also think that, during sleep, our bodies clear toxic waste products from our brains [2].

According to the glymphatic system hypothesis, proteins like β-amyloid, α-synuclein, and tau naturally build up in our brains. Those proteins are strongly linked to neurodegenerative diseases like Alzheimer’s [2]. Other damaging waste products, like reactive oxygen species (ROS), are also produced as our brains function [3].

Your glymphatic system is a bit like a dishwasher. Cerebrospinal fluid (CSF), which is produced by a part of your brain called the choroid plexus, mixes with fluid that surrounds your brain tissue [3]. It then circulates through your brain, carrying all those waste products out and down into your lymph nodes [3]. When you sleep, your glymphatic system works much more efficiently.

Another way sleep could keep your brain healthy is synaptic homeostasis. Think back to your biology classes in school. Do you remember your synapses – those tiny connections between neurons that are responsible for learning and memory? As you move through your day, some synapses get denser and stronger, which requires more energy to maintain and can lead to changes in other brain cells [4]. Sleep allows your brain to return all your synapses to the same strength and density, improving your brain’s function [5].

What Are the Effects of Sleep Deprivation?

In some ways, how sleep supports brain health doesn’t matter. We know that it does – across many different dimensions. Studies have shown that not getting enough sleep can [6]:

• make you take more risks
• slow your reaction times
• reduce your processing speed
• lead to less moral decision making
• impair memory consolidation
• reduce your recall
• shorten your attention span.

In other words, both short- and long-term sleep loss lead to significantly worse cognition. Not getting enough sleep makes our brains less effective.

What Is Dementia?

Major neurocognitive disorder (dementia) can be caused by various health conditions. The most common cause, though, is Alzheimer’s disease, which is responsible for 70 to 80% of cases [7].

In its early stages, Alzheimer’s has no symptoms. As it progresses, it begins to affect things like memory, executive function, and speech [8]. Those symptoms get worse at a rate of about 10% a year, eventually leading to severe memory impairment, speech loss, sleep fragmentation, and hallucinations [8].

Scientists still can’t agree on exactly what causes Alzheimer’s. The most widely accepted idea is the amyloid hypothesis [8]. According to that theory, β-amyloid – one of the toxic proteins we talked about earlier – builds up over time, killing your brain cells.

How Lack of Sleep Contributes to Dementia

We might not know exactly how dementia works, but we do know that poor sleep plays a role. Many studies have shown that getting less sleep earlier in life is linked to a greater risk of dementia as we get older [9, 10, 11].

One study, for example, found that people with sleep disturbances – like insomnia, sleep apnoea, and moving during sleep – were nearly 1.5 times as likely to develop Alzheimer’s disease [12]. Another study found that a 1% decrease in slow-wave sleep each year over 17 years was associated with a 32% increase in the risk of Alzheimer’s [13].

The main culprits are the proteins we talked about earlier: β-amyloid and tau. Lack of sleep means our bodies can’t get rid of them as effectively. Over time, that leads to a toxic buildup, which causes dementia [10]. Inflammation and blood–brain barrier integrity (both of which are affected by sleep) might also play a role [10].

Interestingly, it’s not just how long we sleep that matters. An irregular sleep–wake schedule (a weak circadian rhythm) has been associated with a higher risk of dementia as well [14].

Dementia’s Effect on Sleep

Sleep and dementia don’t have a one-way relationship. Dementia can also disrupt sleep, worsening sleep quality and increasing the risk of sleep conditions [16].

Some studies have found, for example, that over 50% of people with dementia experience obstructive sleep apnoea [17]. Other sleep conditions commonly associated with dementia include [18]:

• fragmented sleep
• talking or walking while asleep
• restless legs.

Those conditions can then lead to daytime sleepiness and naps, which make it harder to fall asleep at night, which then leads to even worse daytime sleepiness … it’s a vicious spiral.

Why does Alzheimer’s disease affect sleep? We don’t exactly know. One major contributor could be circadian rhythm disruption [16]. Because people with dementia are less likely to get natural light, exercise, and eat at the right times, their circadian rhythms may be weaker.

How to Protect Your Brain Health

If you’ve read this far, you probably have one big question: how can I keep my brain as healthy as possible for as long as possible? Luckily, there’s a simple solution.

Scientists have discovered a revolutionary new treatment that makes you live longer. It enhances your memory and makes you more creative. It makes you look more attractive. It keeps you slim and lowers food cravings. It protects you from cancer and dementia. It wards off colds and the flu. It lowers your risk of heart attacks and stroke, not to mention diabetes. You’ll even feel happier, less depressed, and less anxious.

That’s a quote from one of the world’s leading sleep scientists, Dr Matthew Walker [19]. He’s talking about sleep. Getting a good night’s rest is, undoubtedly, the best way to protect yourself from dementia. As you now know, failing to sleep well might actually cause Alzheimer’s.

If you’re struggling to get the sleep your body needs, try these 10 sleep hygiene steps:

1. Make sleep your priority. If you do one thing each day, make it a good sleep.
2. Go to bed and wake up within +/- 30 minutes of the same time each day.
3. Go outside and get direct sunlight (no sunglasses) within 30 minutes of waking up. If you can’t, use a SAD lamp instead.
4. Create a sleep sanctuary. That means investing in a high-quality sleep surfacein a cool, dark, distraction-free space.
5. Avoid bright lights (especially screens) at least 1.5 hours before bed.
6. Have a sleep routine. Set aside an hour to relax and unwind (without screens) before bed.
7. Avoid heavy meals, alcohol, and exercise at least 2 hours before bed.
8. Avoid caffeine and naps at least 6 hours before bed.
9. Ask your doctor about the sleep impacts of any medication.
10. Don’t lie in bed awake. If you can’t sleep for 20 minutes or more, get up and do a relaxing activity until you feel sleepy.

Still worried? These 10 brain health tips can also help.

1. Do at least 150 minutes per week of moderate-intensity aerobic exercise [20, 21]. (Keep in mind that ‘moderate intensity’ just means getting your heart rate into Zone 2 or above – depending on your fitness level, that could be as little as a brisk walk for around 20 minutes a day.)
2. Get 80% of your calories from single-ingredient foods (fruits, vegetables, cereals, meat and fish, eggs, dairy, nuts and seeds).
3. Eat at least 1.6 grams of protein per kilogram of body weight per day.
4. Consume one to 2 grams of omega-3 fatty acids per day.
5. Get 30 ‘plant points’ per week. Memory Morsels has many plant-rich, brain-focused recipes.
6. Consume at least 0.75 grams of fibre per kilogram of bodyweight per day.
7. Challenge your brain with exercises and new experiences. The BrainHQ app, for example, lets you play one free brain game per day.
8. Avoid alcohol, tobacco, and recreational drugs as much as possible.
9. Socialise with someone other than your partner (if you have one) for at least 2 hours per week. Try to catch up in person rather than over technology.
10. Lower your stress levels by trying meditation or mindfulness. You can find various free mindfulness exercises here and here. If you prefer a guided experience, apps like Waking Up can be good options.

Bonus tip: keep passive screen time to under one hour per day. (‘Passive’ means time that you’re not working, creating, or talking to other people.) Science shows that, even in adults, it can shrink important parts of your brain – and lead to an increased risk of dementia.

The information contained in this article is general information only. It should not be construed or used as medical or healthcare advice. For personalised advice, book a consultation with a qualified and registered medical or allied healthcare professional.