Not sleeping enough can increase the risk of developing dementia later in life, according to a new study that found those getting under six hours were most at risk.
Researchers from the University of Paris analysed survey data on the health of 7,959 British individuals since 1985, including self-reported sleep durations.
The team, led by Severine Sabia found that those aged 50 to 70 who got fewer than six hours sleep a night in middle-age had a 30 percent higher risk of late-onset dementia.
Globally, around 50 million people have dementia, and there are nearly 10 million new cases every year, according to the World Health Organisation (WHO).
Sabia says sleep may be important for brain health in midlife, and that future research could establish whether improving sleep habits could prevent dementia.
A common symptom of dementia is altered sleep, but researchers say there is evidence sleep patterns before dementia onset may contribute to the disease.
For this study, authors examined data gathered over the past 36 years since 1985 on thousands of people who self reported their sleeping habits and duration, with some wearing watch accelerometers overnight to confirm this was an accurate estimate.
‘Whether sleep parameters also affect late-life dementia remains the subject of debate,’ according to Sabia and colleagues.
They found that dementia is known to affect sleep-wake cycles, but the extent to which sleep duration as an adult is associated with dementia was unclear.
This is because most studies have not explicitly considered age at assessment of sleep duration or the length of follow-up.
“Our approach pays attention to both these aspects along with inclusion of a wide array of covariates to show that short sleep duration in midlife is associated with an increased risk of dementia,” the team explained.
It is known that during sleep, toxins are cleared out from the brain and other parts of the body – protecting against a host of illnesses including heart disease and cancer.
Dr Sabia said: “There are plausible biological hypotheses to explain the link between sleep duration and dementia.
“One of them concerns the role of sleep in clearance of protein waste in the brain.
“During a waking period neuronal activity increases release of beta amyloid proteins, these proteins are then washed away from the brain during sleep.
“In the case of short sleep, clearance of these proteins might be altered and lead to accumulation of Amyloid beta in the brain.
“Accumulation of these proteins are observed in Alzheimer’s. Other mechanisms might also involve a role of sleep in neuroinflammation and atherosclerosis (hardening of the arteries).”
The NHS says most adults need between six and nine hours of sleep every night. The Sleep Foundation in the US advises seven to eight hours specifically for over 65s.
More than 920,000 people in the UK are living with dementia – a figure expected to soar to two million by 2050 because of the ageing population.
With no cure in sight, there is an increasing focus on lifestyle changes that can help protect against it. In the UK, six in ten adults admit they don’t get enough sleep.
Sara Imarisio, head of research at Alzheimer’s Research UK, said: “We know that the diseases that cause dementia start up to two decades before symptoms like memory loss start to show, so midlife is a crucial time for research into risk factors.
“In this study, sleep duration was largely measured through study volunteers self-reporting their sleep duration,” Imarisio explained.
“And while this group of volunteers was not reflective of the UK population, it does offer insight into the relationship with sleep and dementia in mid to later life.”
She said the study couldn’t ‘tease apart’ the actual cause and effect, but did suggest a persistent lower sleep duration was linked to increased dementia risk.
In contract “it did not find an association between longer than average sleep duration and dementia risk,” she said.
“While there is no sure-fire way to prevent dementia, there are things within our control that can reduce our risk.
“The best evidence suggests that not smoking, only drinking in moderation, staying mentally and physically active, eating a balanced diet, and keeping cholesterol and blood pressure levels in check can all help to keep our brains healthy as we age.”
Elizabeth Coulthard, a dementia neurologist at the University of Bristol, not involved in this study said the team present new information on sleep and dementia.
“This means that at least some of the people who went on to develop dementia probably did not already have it at the start of the study when their sleep was first assessed,” based on 30 years of tracking data, she explained.
“So, it strengthens the evidence that poor sleep in middle age could cause or worsen dementia in later life.”