Poor sleep can increase your risk of dementia - so how much shut-eye should we be getting? Photo / 123RF
Poor sleep can increase your risk of dementia - so how much shut-eye should we be getting? Photo / 123RF
We all know that after a bad night’s sleep, we feel below par the next day, with our energy, mood and ability to concentrate all impacted. But over longer periods, poor sleep can have serious long-term implications for our cognitive health, increasing our risk of dementia.
A growing body of research has linked sleep problems with the brain disease, including a study by University College London and the French National Institute of Health and Medical Research (Inserm) which found that people getting six hours of sleep or less in midlife were 30 per cent more likely to be diagnosed with dementia than those getting seven hours or more.
Scientists believe the reason is that sleeping fewer hours means getting less deep sleep. During this phase of our sleep, our brains are believed to go through a process of “deep washing”, clearing out toxins which, if they accumulate, can lead to dementia. “Our sleep in our 50s and 60s can have a major impact on our risk of developing dementia,” says Dr Severine Sabia, who led the Inserm and UCH study. “That’s why it’s so important to establish good sleep habits during this time.”
Get an early night – but not too early
The timing of our sleep plays a significant part in its quality, since the shift from deep sleep to REM sleep happens at certain times of the night, regardless of when we go to bed – so if we miss the window, we drastically reduce the slow wave phase.
Deep sleep is important for your overall health. Photo / Getty Images
One study by researchers in China, Sweden and Britain showed a link between going to bed very early and dementia, with every hour extra in bed before 10pm associated with a 25 per cent increased risk of the disease. However, it’s not yet known whether it’s sleeping too long that heightens the risk, or whether sleeping longer is an early warning sign of a disrupted circadian rhythm and the first stages of the disease.
Turning in before midnight – ideally at 10-11pm – is optimal to give ourselves the best possible chance of enough deep sleep before our alarm goes off.
What is deep sleep?
This is the phase of sleep, also known as “slow wave sleep” or stage three, in which the glymphatic system is most active and this “deep washing” occurs.
Throughout the night, we move through between four and six cycles consisting of different stages of sleep, including light phases, rapid eye movement (REM) and deep sleep. We usually descend into deep sleep within an hour of falling asleep, and experience progressively shorter periods of it as the night wears on.
According to the Sleep Foundation, the ideal amount of deep sleep is 1.4-2 hours, or 20-25 per cent of our overall sleep. However, the amount a person gets can vary depending on factors including age, genetics and lifestyle.
“Most sleep cycles last between one and two hours, and if we lose even half an hour of sleep, we might lose the deep sleep part which is vital for the brain’s cleaning,” says Dr Sabia.
Deep sleep ‘washes out’ brain toxins
Although scientists have long known about the restorative properties of sleep, it was in 2013 that a team from the University of Rochester Medical Centre in the US identified a system in the brain akin to a dishwasher’s rinse cycle, which is activated during sleep. They found a series of tiny channels surrounding the brain’s blood vessels that allow pulses of cerebrospinal fluid to wash in and be pushed through the brain tissue. As it leaves, it carries the day’s metabolic waste with it.
They named it the glymphatic system because of its similarity to the body’s lymphatic network, except managed by the glial cells, which support the brain’s neurons.
Brain changes associated with dementia disrupt deep sleep. Photo / 123RF
“The brain isn’t like other organ systems, such as the liver, where cells regenerate – our neuron levels aren’t replenished,” says Dr Ahmad Khundakar, a senior lecturer in biomedical science at Teesside University, whose specialism is dementia and neuroscience. “Because of that, if proteins build up, they can eventually cause neurodegeneration. The glymphatic system is very important as a clearance mechanism to flush out these proteins.”
In turn, brain changes associated with dementia also disturb sleep, disrupting the synchronised brain waves which happen during deep sleep – a vicious cycle, which prevents the glymphatic system working properly.
In people with Alzheimer’s, abnormal levels of beta-amyloid protein clump together to form plaques. Tau protein also accumulates and begins sticking together in tangles. These harm the communication between neurons, eventually causing them to die off and the brain to shrink.
Another protein, alpha-synuclein, is naturally abundant in our brains but in many people with Parkinson’s, it clumps together in masses called Lewy bodies.
“Often, we see a combination of different protein build-ups in the brains of people with dementia,” he says. “It’s very rare that you get pure Alzheimer’s or pure Parkinson’s.”
Why do we get less deep sleep as we age?
Babies and children have a large amount of slow wave sleep, before this begins to decline from early adulthood onwards. As we age, we begin to have relatively short periods of slow-wave sleep and fewer of them, making our sleep lighter and more fragmented. Although the reason is not yet fully understood, it is thought to be due to the lower levels of growth hormone and melatonin our bodies produce. “Our circadian rhythm is disrupted as we grow older, and that deeper sleep is harder to reach,” says Dr Sabia.
While many of us tend to assume poorer sleep is a natural part of ageing, Dr Sabia urges over-50s to do everything they can to strive for more deep sleep.
“There are so many reasons for us not to get enough quality sleep – we live in a society where it isn’t prioritised,” she says. ‘But it is essential for brain health.”
1. Get into daylight every morning
If we do one thing to improve our sleep, she advises: “Get up at the same time every day and get outside into daylight to regulate your circadian rhythm.”
Studies have shown that bright light therapy, in which people with dementia sit in front of a light box for 30 minutes every morning, can help reduce their sleep disturbances by reinforcing their body clock. Scientists are currently exploring whether this kind of therapy could be used to prevent the disease.
In the meantime, research has proved that making efforts to regulate our circadian rhythm, including exposure to natural light in the daytime, avoiding blue light from screens before bedtime and blocking out light at night using an eye mask or blackout blinds, can help us get better-quality, deeper sleep.
It’s tempting, following a restless night, to try to catch up the following day, but this doesn’t offer the same brain benefits as night-time sleep, says Dr Sabia.
“Napping doesn’t result in the same deep cleaning as happens during the night,” she says. “It can also interfere with good quality nighttime sleep, particularly if you enter deep sleep during the nap as this means getting less deep sleep at night.”
3. Try pink noise
Sleep researchers at the University of Cardiff are working on sounds that may help to boost deep sleep, including soft “clicks” played to sleepers as they approach the peak of their brain activity during slow wave sleep. Their research has shown this can increase deep sleep.
Until the technique is marketed as a gadget we can use at home, it’s worth trying pink noise. A small recent study by researchers in Zurich found that playing pink noise, which includes sounds such as falling rain, a flowing river, crashing ocean waves or rustling leaves, enhanced slow wave brain activity during deep sleep in some participants.
Moderate drinking has not been linked to an increased risk of dementia, but research has proved a link between alcohol and diminished sleep quality.
Drinking tends to increase slow wave sleep in the first half of the night, but in the second half, all stages of sleep are disrupted, leading to frequent wakings. Ideally, it’s best to avoid alcohol for three hours before bed. Avoiding caffeine for at least seven hours before bedtime is also recommended, as it significantly reduces slow wave sleep.
