Sleep deprivation may boost dementia risk

Could getting too little sleep increase your chances of developing dementia?

For years, researchers have pondered this and other questions about how sleep relates to cognitive decline. Answers have been elusive because it’s hard to know if insufficient sleep is a symptom of the brain changes that underlie dementia — or if it can actually help cause those changes.

Now, a large new study reports some of the most persuasive findings yet to suggest that people who don’t get enough sleep in their 50s and 60s may be more likely to develop dementia when they’re older.

The research, published Tuesday in the journal Nature Communications, has limitations but also several strengths.

It followed nearly 8,000 people in Britain for about 25 years, beginning when they were 50. It found that those who consistently reported sleeping six hours or less on an average weeknight were about 30 percent more likely than people who regularly got seven hours of sleep to be diagnosed with dementia nearly three decades later. (Seven hours was defined as “normal” sleep in the study.)

“It would be really unlikely that almost three decades earlier, this sleep was a symptom of dementia, so it’s a great study in providing strong evidence that sleep is really a risk factor,” said Dr. Kristine Yaffe, a professor of neurology and psychiatry at the University of California, San Francisco, who wasn’t involved in the study.

Pre-dementia brain changes such as accumulations of proteins associated with Alzheimer’s are known to begin about 15 to 20 years before people exhibit memory and thinking problems, so sleep patterns within that time frame could be considered an emerging effect of the disease.

That has posed a “chicken or egg question of which comes first, the sleep problem or the pathology,” said Dr. Erik Musiek, a neurologist and co-director of the Center on Biological Rhythms and Sleep at Washington University in St. Louis, who wasn’t involved in the new research.

“I don’t know that this study necessarily seals the deal, but it gets closer because it has a lot of people who were relatively young,” he said. “There’s a decent chance that they are capturing people in middle age before they have Alzheimer’s disease pathology or plaques and tangles in their brain.”

Drawing on medical records and other data from a prominent study of British civil servants called Whitehall II, which began in the mid-1980s, the researchers tracked how many hours 7,959 participants said they slept in reports filed six times between 1985 and 2016. By the end of the study, 521 people had been diagnosed with dementia at an average age of 77.

“It’s always difficult to know what to conclude from these kinds of studies,” wrote Robert Howard, a professor of old age psychiatry at University College London, one of several experts who submitted comments about the study to Nature Communications. “Insomniacs — who probably don’t need something else to ruminate about in bed — shouldn’t worry that they are heading for dementia unless they get off to sleep immediately.”