That doesn’t mean middle-aged short sleepers should panic, according to experts. Although the study is an important step forward, much about the connection between sleep and dementia remains unknown, they said. Still, it can’t hurt to work on your sleep habits while research continues, and you’ll find some strategies listed below.
In the study, European researchers followed nearly 8,000 people in Britain for 25 years, starting when subjects were 50. They found that those who consistently got six hours of sleep or less per night in their 50s and 60s were about 30 percent more likely to develop dementia later in life, compared to those who logged seven hours of sleep per night. That was independent of “sociodemographic, behavioural, cardiometabolic, and mental health factors,” the study authors wrote. Findings were published in the journal Nature Communications in late April.
“This is just another example of the importance of appropriate sleep for brain health,” said Michael V. Vitiello, a professor of psychiatry and behavioral sciences at the University of Washington at Seattle and member of the SleepFoundation.org medical advisory board, who wasn’t involved in the study. “It’s really important for people to be conscious of making sure that they sleep well. It’s not trivial, and it shouldn’t be the last thing you think about. It shouldn’t be the thing you sacrifice.”
Lack of sleep might increase dementia risk by impairing learning and memory development, said study author Andrew Sommerlad, an old-age psychiatrist at University College London, or it could affect the brain’s ability to clear harmful protein waste products.
Researchers have spent years trying to understand the sleep-dementia connection, a quest that becomes more urgent as the number of people with Alzheimer’s disease balloons. More than 6 million Americans are living with the disease, according to the Alzheimer’s Association, and by 2050, that number is expected to reach nearly 13 million. Yet, it’s a difficult area in which to draw conclusions.
Earlier this year, Charles Czeisler, chief of the sleep and circadian disorders division at Brigham and Women’s Hospital in Boston, co-authored a similar study that found that adults age 65 and older who got five hours or less of sleep per night had double the risk of dementia than those who clocked seven or eight hours per night. Results were published in the journal Aging.
“At this point, it’s too early to say that behavior X leads to Y,” Czeisler said. “But the association certainly reveals the importance of continuing to study the relationship.”
One of the challenges to studying the link between sleep and cognitive decline is that it’s difficult to determine what happens first: Is too little sleep a symptom of the brain changes that often begin decades before cognitive problems appear? Or does it cause those changes? So far, that’s still unclear, said Claire Sexton, director of scientific programs and outreach with the Alzheimer’s Association.
“There’s mounting evidence pointing toward the relationship between sleep and dementia,” she said. “But there are a lot of unanswered questions. There’s no one factor that would guarantee someone will develop dementia, and there’s no one factor that will guarantee someone won’t.”
Vitiello lauded the new study’s lengthy follow-up period and examination of people in their 50s (most similar research focuses on those 65 and older). But he emphasized that the findings estimate increased risk for the entire population, not for any one individual. “These are predictions,” he said. “On average, if you have this kind of disturbed sleep, your odds go up this percentage. It doesn’t mean that just because you’re a 55-year-old sleeping under six hours a night, you’re guaranteed to have an increased Alzheimer’s risk of 30 percent.”
Exactly why someone is a short sleeper — for example, if they have insomnia, hold multiple jobs that require odd hours or naturally need less sleep — likely plays a role in their unique risk, he added. The study didn’t account for those factors.