Sleep Better for Brain Health

New research shows adequate sleep lowers the risk of dementia.

More than one-third of the US population reports getting less than the recommended seven hours of sleep per night. Inadequate sleep is known to increase oxidative stress and anxiety levels and can have a negative effect on many aspects of health, including blood pressure, heart rate, hormones, immune function, and mental health. People who sleep less than seven hours per night are at higher risk for chronic health conditions such as arthritis, diabetes, and asthma. Now, research is showing sleep has another important function: keeping the brain healthy and protecting against dementia.

A new study, conducted by a team of European researchers and published in April 2021 in Nature Communications, examined about 8,000 participants over 25 years and concluded that short sleep duration in middle age is associated with an increased risk of dementia. The researchers found that consistently sleeping six hours or less at age 50, 60, and 70 was associated with a 30% increase in dementia risk compared to a normal sleep duration of seven hours, even after accounting for sociodemographic, behavioral, cardiometabolic, and mental health factors. About half of participants wore a sleep tracking device to confirm their questionnaire data.

This study builds on other research linking poor sleep and dementia. A Harvard Medical School study, published in Aging in February 2021, involving more than 2,800 participants aged 65 and older, found those who slept fewer than five hours per night were twice as likely to develop dementia and twice as likely to die, compared to those who slept six to eight hours per night. Another large UK study found an elevated risk for cognitive decline for those who sleep too little as well as those who sleep too much. That study concluded the optimal amount of sleep for cognitive health is between seven and eight hours per night.

Researchers do not fully understand why inadequate sleep increases the risk for dementia, but the newest research suggests the link may be due to several processes, including neuroinflammation, atherosclerosis, and impaired beta-amyloid clearance.

Much research has focused on impaired amyloid clearance as a contributor to the development of Alzheimer’s. Beta-amyloid is a protein that is thought to be a metabolic waste product created when brain cells communicate. These amyloid proteins accumulate in the brain daily and any excess are flushed out during deep sleep. Some studies suggest that interruption of deep, or slow-wave, sleep can cause a build-up of amyloid proteins that form a plaque on brain tissue, hindering communication between neurons.

“Observational studies have found that adults over age 65 with amyloid plaques in their brain have reduced slow-wave sleep, which is thought to play an important role in memory function, even though these people do not yet show signs of Alzheimer’s, like memory loss and cognitive decline,” says Dr. Brad Dickerson, associate professor of neurology at Harvard Medical School. A 2015 study in Nature Neuroscience examined brain scans that measured amyloid levels in a group of older adults who did not have dementia or sleep problems. The scans were done before and after eight hours of sleep. The participants were asked to memorize 120 pairs of words and were tested on how well they remembered them. Those with the highest levels of amyloid in the brain in the morning had the poorest quality of sleep and performed worst on the memory test.

That study concluded the optimal amount of sleep for cognitive health is between seven and eight hours per night. 

A subsequent study of beta-amyloid, published in 2018 in Proceedings of the National Academy of Sciences, scanned participants’ brains after a full night’s sleep and after a night of sleep deprivation—about 31 hours without sleep. After losing one night of sleep, the amount of beta-amyloid in participants’ brains increased about 5%, specifically in the areas of the brain associated with damage in the early stages of Alzheimer’s disease, the thalamus and hippocampus.

A 2013 study of people who had an increased genetic risk of developing Alzheimer’s found that better sleep not only reduced the likelihood of developing clinical Alzheimer’s disease, it also reduced the development of neurofibrillary tangles, another substance that accumulates in the brains of people with Alzheimer’s disease.

David Perlmutter, MD, a renowned neurologist whose expertise includes preventing neurodegenerative disorders, says the research connecting dementia risk with sleep duration in midlife—and possibly earlier—makes clear the need to “do everything we possibly can to get a good night’s sleep.”

Dr. Perlmutter recommends using a wearable device to track sleep in order to see how changes in lifestyle are reflected in sleep parameters such as length and quality of sleep. Some lifestyle modifications he recommends for improved sleep include limiting afternoon coffee consumption, reducing exposure to blue light from electronics in the evenings, lowering the temperature in the bedroom for sleep, and, if needed, using a sleep aid supplement such as melatonin.

Aerobic exercise and eating right can also lower the risk of dementia. “Exercise also helps with better sleep quality,” says Dr. Dickerson of Harvard. “Weight loss also plays a factor, as people who are overweight tend to have more sleep problems.”

Mind-body interventions have been shown to improve sleep quality, reduce sleep disturbances, and treat insomnia. A 2020 systematic review and meta-analysis evaluated mind-body interventions that included Tai Chi/Qigong and yoga/pilates and found they improved sleep quality compared to those who did not do any exercise.

Symptoms such as insomnia, sleep apnea, and waking up frequently to use the bathroom should not go untreated.

A 2020 randomized clinical trial examined the impact of yogic meditation on sleep quality in healthy adults. The participants in the intervention group received two 30-minute yogic meditation classes per week for eight weeks. Those in the meditation group fell asleep faster, experienced fewer sleep disturbances, and improved sleep quality compared to the control group. A 2015 randomized clinical trial, published in JAMA, found practicing 10-30 minutes of mindfulness exercises, such as meditation or mindful movement, was superior to sleep hygiene education for improving sleep. The group that practiced mindful awareness had a significant improvement in insomnia symptoms and fatigue severity.

Researchers are quick to point out that the link between sleep and dementia is bi-directional—for example, elevated beta-amyloid may also lead to trouble sleeping. While more long-term studies are warranted, the clear implication of the research is: It is never too soon to improve sleep habits. Experts say symptoms such as insomnia, sleep apnea, or waking up frequently to use the bathroom should not go untreated. Getting a sleep evaluation may go a long way toward protecting brain health in the future.