In April 2021, scientists found a link between a lack of sleep and an increased risk of dementia. According to research published in the scientific journal Nature Communications, middle-aged adults who sleep six hours or less a night were more likely to be diagnosed with dementia.
The findings from the 25-year-long study were covered by a wide variety of news outlets, including The New York Times and The Jakarta Post. International coverage prompted some Snopes readers to ask us if it was true.
We found that it was. But some important caveats should be noted, particularly the fact the data collected could not prove cause and effect — only suggest a link between sleep and dementia as people age.
Dementia is a syndrome caused by a deterioration in memory, thinking, behavior, and the ability to perform everyday activities. Globally, around 50 million people have dementia, most commonly Alzheimer’s, and the World Health Organization estimates nearly 10 million new cases are diagnosed each year. People with dementia often have issues with sleep. However, the Alzheimer’s Society reports that the evidence is unclear on whether poor sleep is a risk factor for dementia.
“Sleep and dementia is a complicated topic. Different types of dementia are associated with different sleep problems. Researchers are also not yet sure which way the interaction goes — whether poor sleep causes or exacerbates dementia or if dementia leads to poor sleep,” wrote the UK-based society, adding that both theories could be true and the relationship “could be circular.”
To determine how sleep patterns might influence the risk of dementia, scientists at the French research institute INSERM analyzed data from the Whitehall II study, a long-term health study conducted by University College London that followed the health of nearly 8,000 British people since 1985.
Participants self-reported sleep duration, and about half wore devices during sleep that confirmed sleep estimates at six intervals throughout the course of the more than 25-year study; survey respondents also were asked how many hours of sleep they averaged per weeknight. This data was then compared with national health registries that identified dementia cases among survey respondents, including the Mental Health Services Data Set, a national database that contains information on dementia for persons in contact with healthcare providers.
A higher risk of dementia was identified in those who slept six hours or less each night when in their 50s and 60s when compared with those who slept an average of seven hours. Researchers also found a 30 percent increased risk of dementia in those with “persistent short sleep” from the age of 50 to 70, regardless of cardiometabolic and mental health issues, both known risk factors for dementia.
A similar study published in February 2021 in the journal Aging also found that older adults who get little sleep at night may be at a heightened risk of dementia or earlier death. In a study of 2,800 older Americans, those who slept no more than five hours a night were more likely to develop dementia or die in the following five years — a risk that was more than double that of those who slept seven to eight hours a night.
Though neither of the studies establishes a causal relationship — that a lack of sleep causes dementia — the research offers insight into understanding how sleep and dementia may be related to one another, particularly as individuals age.
“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,” said Dr. Sara Imarisio, head of research at Alzheimer’s Research UK, in a statement.
Imarisio, who was not involved in either study, said no “magic bullet” can prevent dementia, but individuals can reduce their 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,” said Imarisio.