We’ve all felt the effects of a poor night’s sleep. We expect fatigue, but brain fog, slow reflexes, lack of focus, and even memory gaps that follow a night of tossing and turning can be daunting. Driving while tired is just as dangerous as driving under the influence of alcohol. Fortunately, we can rest easy knowing that the next good night’s sleep will restore our faculties, but be aware, a consistent lack of sleep quality may significantly affect brain function over the long term.

Evidence now points to sleep quality as a predictive factor in the development of dementia, specifically Alzheimer’s disease (AD), the most common form of age-related memory loss. One long-term study followed middle-aged men, who were initially cognitively healthy, for an average of 40 years. It found that participants who reported more sleep disturbances over time had an increased risk of developing dementia later in life.

Correlation doesn’t prove causation, however. Changes in sleep-wake cycles are known in people who already have AD. Just because people who sleep poorly are more likely to develop dementia later, doesn’t mean that the lack of sleep has a negative effect on brain health over the long term. Perhaps people predisposed to AD also tend to sleep poorly. However, shorter-term studies suggest a causative connection between inadequate sleep and cognitive health. One study revealed that just a single night of experimentally interrupted sleep in young men resulted in higher tau levels, a brain protein marker for Alzheimer’s disease.

Stages of slumber

Sleep is a dynamic process. We pass through several different stages and phases throughout the night, each characterized by distinct electrical activity patterns in the brain. Early in the night, we tend to spend more time in deep, non-dreaming sleep. It is specifically a lack of, or interruption in, this type of so-called slow-wave sleep (SWS) linked to problems with long-term brain health. A 2019 study showed that seniors who spent less time in this type of sleep developed higher levels of abnormal brain proteins linked to AD.

One reason a lack of deep sleep might predispose someone to dementia is because that specific period of rest is when the brain eliminates toxic by-products as part of normal metabolism. Accumulating cellular junk that is not removed regularly can be a source of free radicals and inflammatory compounds that interfere with neurons’ optimal functioning. Nightly cerebral housekeeping that occurs primarily during deep sleep is key to brain health maintenance.

To complicate matters, since older people tend to sleep less and more lightly, the chicken-and-egg principle is likely at play here in the later decades of life.

Better sleep now

Increasing the time spent in slow wave sleep (SWS) may one day be a therapeutic target for preventing or managing Alzheimer’s. The good news is that you don’t have to wait for a new drug or gadget to get you there. Physical exercise and socializing lengthen the time spent in the deepest sleep stages. Supplemental magnesium increases SWS in people 60–80 years old.

There’s more to learn about the impact of sleep on cognitive function. Regular good rest may be critical for preserving mental sharpness with age. We all experience the occasional bad night, but if lack of sleep is a regular occurrence for you, it is worth taking steps to improve your sleep quality. Your brain will thank you.