En español | People who regularly slept six hours or less a night in their 50s, 60s and 70s were about 30 percent more likely to develop dementia than those who slept seven hours, a newly published study has found. The increased risk persisted even when scientists accounted for physical and mental health, as well as genetic risk for Alzheimer’s disease.
Other studies have uncovered associations between sleep problems and dementia, but the link has remained unclear. This report, however, offers a unique advantage over earlier ones, lead investigator Séverine Sabia told AARP.
“Most previous studies were based among individuals aged 65 or older,” said Sabia, an epidemiologist at French Institute of Health and Medical Research (INSERM) in Paris and at University College London, England. “The novelty of this study is that its long follow-up period allowed us to assess the association of sleep duration at age 50 and dementia risk in later life.”
What the researchers found was a “consistent association between persistent short sleep duration between age 50 and 70 and increased risk of dementia,” Sabia said.
Short sleep could contribute to disease development
Although scientists have long acknowledged the association between disturbed sleep and dementia, they haven’t been able to solve a crucial riddle: Are sleep problems contributing to the onset of dementia, or could they be an early sign that something is amiss in the brain?
While Sabia’s study doesn’t nail this conclusively, it does strongly suggest that persistent short sleep in midlife might be a key driver of dementia decades later, said Brendan Lucey, M.D., associate professor of neurology at the Washington University School of Medicine and an expert in the relationship between sleep and Alzheimer’s disease.
“They began monitoring sleep quality many years before any symptoms and probably before much of the pathology was developing,” he explained. “It’s not a definitive study, but to me it does provide compelling evidence that short sleepers might be at an increased risk.”
Sabia and her colleagues followed nearly 8,000 people in Britain for about 25 years and assessed their sleep patterns, starting at age 50. Participants reported their sleep duration and quality in real time at six points over the course of the study, and more than half of the subjects wore an accelerometer — a device that detects periods of motion and stillness — to record their sleep during the 2012-2013 reporting cycle.
By the end of the study, 521 subjects had developed some type of dementia; the average age at diagnosis was 77. What’s more, those who reported short sleep had a significantly increased risk of developing some form of dementia. At age 50, compared to normal sleepers, short sleepers faced a 22 percent increased risk. At age 60, the increased risk was 37 percent, and at age 70, it was 24 percent. All of the associations remained strong even after the team took into account physical and mental health, genetic risk for Alzheimer’s disease, and sociodemographic factors.
Sabia and her team also looked to see if changes in sleep patterns had any effect on developing dementia. Regardless of age, people who had persistent short sleep patterns were at the highest risk — 30 percent more likely to develop dementia than people with normal sleep.
The study didn’t break out different types of dementia, so there’s no way to know for sure how many people developed Alzheimer’s disease, or how many developed dementia as a result of cardiovascular disease or other neurocognitive disorders. But by using a diagnosis of dementia with no history of cardiovascular disease, the team estimated that 77.5 percent of the dementia cases (404) were Alzheimer’s. When they examined sleep patterns just in that group, the risk picture was similar.
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Sleeping gives the brain a chance to clean up
Lack of sleep could influence dementia risk in several ways. One of the most-studied mechanisms involves the brain’s nightly cleaning cycle, Lucey said.
“When we’re asleep, there’s an increased flow of fluid through the brain, and this is hypothesized to clear out waste products and lower their concentration,” he explained.
Among the waste products lowered by sleep are the proteins beta amyloid and tau. At night, both of these proteins are released less and cleared more. In people who develop Alzheimer’s, both proteins build up to dangerous levels. Beta amyloid forms sticky clumps that interfere with signaling between neurons, and tau forms tangled knots that kill the neuron itself. When these proteins can’t be normally removed, they may be more likely to eventually begin sticking together into pathological forms, Lucey said.
Other proteins implicated in different kinds of dementia also follow this circadian waste removal rhythm, he added. “We’ve also looked at alpha synuclein, a protein that is important in both Parkinson’s disease and Lewy body dementia, and whose concentration increases with sleep deprivation.”
Sleep’s effects on cognitive health may range far beyond protein clearance. Inadequate sleep is also associated with atherosclerosis, hypertension, obesity, diabetes and depression — all of which are important risk factors for Alzheimer’s disease and other dementias.
“An important question for the field to study is how sleep disturbance in people with diabetes or obesity changes their risk of developing Alzheimer’s disease,” Lucey said. “Treating sleep disorders may be even more important in these individuals.”
Sleep: Just one healthy habit that benefits the brain
“Sleep is one potential risk factor associated with dementia, but it’s not the only one,” said Claire Sexton, director of scientific programs and outreach at the Alzheimer’s Association. Her suggestion: Don’t focus on just one factor. Instead, “try to create a healthy lifestyle that might actually, truly help prevent dementia.” A nutritious diet, physical activity and social engagement have also been linked to better brain health.
The Alzheimer’s Association is putting sleep front and center in its own research right now. The group has just launched U.S. POINTER-zzz, a $5.3 million study to examine whether lifestyle changes that might reduce Alzheimer’s risk also improve sleep. U.S. POINTER-zzz is a substudy of U.S. POINTER, a two-year clinical trial testing whether a combination of exercise, diet, mental stimulation and social support can reduce the risk of dementia in people who may be at increased risk for cognitive decline.
U.S. Pointer-zzz is recruiting subjects for the study. You may qualify if you are 60 to 79 years old, not a regular exerciser and have a risk factor for memory loss (family history of memory problems or slightly high blood pressure, cholesterol or blood sugar). You can learn more about U.S. Pointer here.
Sleep-starved? Tips for dealing with insomnia
The bad news: Sleep problems might increase your risk of dementia. The good news? You can do something about it.
“People often think that poor sleep is something that just happens naturally as we get older, that it’s something we have to live with and can’t do anything about,” said Ronald Chervin, M.D., a neurologist and director of the Sleep Disorders Centers at the University of Michigan. “That’s simply not true. Poor sleep is not a feature of getting older. And if you’re not sleeping well, instead of suffering and just accepting it, talk to your primary care doctor or a sleep medicine physician. Usually there is a diagnosis and a treatment available.”
In the meantime, here are some of Chervin’s top tips for improving your sleep.
- Control your environment. A comfortable bed in a cool, dark, quiet room is the most conducive setup for high-quality sleep.
- Limit screen time for an hour or two before bed. “TV is full-spectrum light, and phones and tablets emit a lot of blue light, which can reset our circadian rhythm and delay sleep onset,” he said.
- Avoid stressful mental pastimes before bed. This might mean switching off the TV or closing your book, depending on the content.
- Avoid alcohol for a few hours before bedtime. It’s a sedative, true, but a short-acting one that leaves you vulnerable to abrupt waking once the effect of the alcohol wears off.
- Exercise regularly, but earlier in the day rather than close to bedtime.
- Establish a routine that lets your brain know sleep is coming soon. Set a regular bedtime, and if you are vulnerable to insomnia, set a regular wake-up time.
- Talk to your doctor about cognitive behavioral therapy for insomnia (CBTI). This psychological intervention is part education and part behavior modification. Usually delivered by a trained professional, it can encompass sleep restriction initially while you learn to sleep efficiently again, as well as other techniques that have been demonstrated by years of research to help restore — and then maintain — healthy sleep.