The New York Times
Sleeping too little in middle age can increase risk of dementia, study finds
Could not getting enough sleep increase your chances of developing dementia? For years, researchers have pondered these and other questions about the link between sleep and cognitive decline. The answers have been elusive because it’s difficult to know if not enough sleep is a symptom of the brain changes that underlie dementia – or if it can actually help trigger those changes. Now, a large new study reports some of the most compelling findings to date, suggesting that people who don’t get enough sleep in their 50s and 60s are more likely to develop dementia when they are older. Sign up for The Morning newsletter from the New York Times. 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, starting when they were 50 years old. It found that those who consistently reported sleeping six hours or less on an average weeknight were about 30% more likely than people who regularly got seven hours of sleep (defined as “ normal ” sleep in the study) nearly three decades later be diagnosed with dementia. . “It would be really unlikely that almost three decades earlier this sleep was a symptom of dementia, so it’s a great study to provide 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 was not involved in the study. Pre-dementia brain changes, such as build-ups of proteins related to Alzheimer’s disease, start about 15 to 20 years before people show memory and thinking problems, so sleep patterns within that time frame can be considered an emerging effect of the disease. That has led to a “chicken or egg question that 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 were not involved in the new investigation. “I don’t know if this research will necessarily seal the deal, but it’s getting closer because there are a lot of relatively young people,” he said. “There’s a decent chance they’ll catch middle-aged people before they have Alzheimer’s pathology or plaques and tangles in their brains.” Based on medical records and other data from a prominent study of British officials called Whitehall II, which began in the mid-1980s, the researchers tracked how many hours 7,959 participants said they slept in reports submitted six times between 1985 and 2016. At the end of the study, 521 people had been diagnosed with dementia at an average age of 77 years. The team was able to adapt to various behaviors and characteristics that could affect sleep patterns or dementia risk, said study author Séverine Sabia, an epidemiologist at Inserm, France’s public health research center. These include smoking, alcohol consumption, how physically active people were, body mass index, fruit and vegetable consumption, education level, marital status and conditions such as high blood pressure, diabetes and cardiovascular disease. To further clarify the relationship between sleep and dementia, researchers separated people who had mental illness before the age of 65. Depression is considered a risk factor for dementia and “mental disorders are quite strongly linked to sleep disturbances,” said Sabia. The study’s analysis of participants without mental illness found a similar association between short sleepers and an increased risk of dementia. The correlation also held whether people were on sleep medications and whether or not they had a mutation called ApoE4 that makes people more likely to develop Alzheimer’s disease, Sabia said. The researchers did not find a general difference between men and women. “The study found a modest, but I would mention a somewhat important association of short sleep and dementia risk,” said Pamela Lutsey, associate professor of epidemiology and community health at the University of Minnesota, who was not involved in the study. “Short sleep is very common and therefore, even if modestly associated with dementia risk, it can be important on a societal level. Short sleep is something we can control, something you can change. Yet, as with other research in this area, the study had limitations that prevented it from proving that insufficient sleep can cause dementia. Most sleep data was self-reported, a subjective measure that is not always accurate, experts said. Nearly 4,000 participants had sleep duration measured by accelerometers, and that data was consistent with their self-reported sleep times, the researchers said.Still, that quantitative measure came late in the study, when participants were about 69, making it less useful than when it was younger. In addition, most of the participants were white and better educated and healthier than the overall UK population. And by relying on electronic medical records for diagnoses of dementia, researchers may have missed a few cases and were unable to identify exact types of dementia. “It’s always hard to know what you’re out of these kinds of studies must conclude, ”wrote Robert Howard, a professor of old age psychiatry at University College London, one of the many experts who submitted comments to Nature Communications on the study. “Insomniacs – who probably don’t need anything else to worry about in bed,” he added, “don’t have to worry about being on the road to dementia unless they fall asleep immediately.” There are compelling scientific theories as to why too little sleep can increase the risk of dementia, particularly Alzheimer’s disease. Studies have shown that amyloid, a protein that clumps in plaques in Alzheimer’s disease, in the cerebrospinal fluid “goes up when you rob people of sleep,” said Musiek. Other studies of amyloid and another Alzheimer’s protein, tau, suggest that “sleep is important for removing proteins from the brain or limiting production,” he said. One theory is that the more people are awake, the longer their neurons are active and the more amyloid is produced, Musiek said. Another theory is that fluid flowing into the brain during sleep helps remove excess protein, so insufficient sleep means more protein build-up, he said. Some scientists also think it may be important to allow enough time in certain sleep stages for protein to clear up. Lutsey said too little sleep can also act indirectly, fueling conditions that are known risk factors for dementia. “Think of someone staying up late and snacking, or because they sleep very little, have low motivation for physical activity,” she said. “That could predispose them to obesity and then things like diabetes and hypertension that have been quite strongly associated with dementia risk.” Another theory is “a shared genetic link,” said Yaffe, “genetic pathways or profiles associated with both shorter sleep and an increased risk of Alzheimer’s disease.” She and others said it is also possible for the sleep-dementia relationship to be “ bidirectional, ” with poor sleep fueling dementia, further reducing sleep, making dementia worse. Experts seem to agree that research into the link between sleep and dementia is challenging and that previous studies have sometimes produced confusing findings. For example, in some studies, people who sleep too long (usually measured as nine hours or more) appear to have a greater risk of dementia, but several of those studies were smaller or had older participants, experts said. In the new study, the results indicated an increased risk for long sleepers (defined as eight hours or more because there weren’t enough nine-hour sleepers, Sabia said), but the association was not statistically significant. Experts said they couldn’t come up with any scientific explanations as to why long sleep would increase the risk of dementia and that it could reflect another underlying health condition. The new study also examined whether people’s sleep changed over time. There seemed to be a slightly increased risk of dementia in people who switched from short to normal sleep, Sabia said, a pattern that she says may reflect sleeping too little by age 50 and needing more sleep later due to developing of dementia. So, if short sleep is a culprit, how can people get more zzz’s? “Generally speaking, sleeping pills and many other things don’t give you that deep sleep,” said Yaffe. And “we really want a deep sleep because that seems to be the time when things are cleared up and it’s restorative.” She said naps are okay to make up for missed sleep, but a good night’s sleep should make naps unnecessary. People with sleep disorders or apnea should consult sleep specialists, she said. For others, Lutsey said, a regular sleep schedule, avoiding caffeine and alcohol before bed, and removing phones and computers from the bedroom are among the Centers for Disease Control and Prevention’s guidelines for “ sleep hygiene. ” But much about sleep remains a mystery. The new study “provides pretty strong evidence that sleep is important in middle age,” said Musiek. “But we still have a lot to learn about and how the relationship actually occurs in people and what we can do about it.” This article originally appeared in The New York Times. © 2021 The New York Times Company