Health

Use Sleep and Exercise to Drop Your Dementia Risk

Too little (or too much) sleep may increase your dementia risk. Optimizing sleep and getting some exercise may reduce risk.

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“Putting both contacts in one eye … almost mistaking nail glue for contact solution … going to sleep and forgetting the dogs were outside in the cold … putting the dust pan in the refrigerator — and the milk on the floor near the broom … looking for my glasses and wearing two pairs on my head … finding the butter in the dish cabinet … wearing a terrific suit and two different black pumps … and finally — going through the drive thru for coffee and ordering from the trash can.”

I love this piece from the Huffington Post, one illustrating some of the perils of sleep deprivation. Today, we look at the relationship between short sleep and dementia. First, I would like to explore one of the primary reasons that we sleep.

Sleep is a waste disposal system

Your brain consumes an immense amount of energy. While it represents only two percent of your body mass, it uses about twenty percent of your energy. This energy use creates a big problem: As the brain’s nerve cells gobble up the power, they produce debris that flows through the brain. This garbage can interfere with the normal functioning of the organ.

Nerve cell waste products include proteins, which, if not dealt with, can form lumps that are bad for the brain. An example is the clumping of a protein known as amyloid-beta. When developing in abundance, this protein can result in suboptimal thinking (including memory problems such as Alzheimer’s dementia).

Spinal fluid flushes our toxic waste

Cerebrospinal fluid flows in and around our brain and spinal cord region’s crevices, carrying nutrients and cushioning our brain. As we sleep, the spinal fluid can flush out toxins that have accumulated during the day. These toxic byproducts include β-amyloid, a central component of Alzheimer’s disease.

This central nervous system waste removal pathway is known as the glymphatic system, which is more active while we sleep: Sleep, glymphatic clearance, and beta-amyloid clearance. Repeat.

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Sleep and memory

Given the brain clean-up occurs during sleep, might inadequate sleep be associated with health issues? Let’s look at the Women’s Health Initiative Memory Study (WHIMS). Participants completed monthly questionnaires and had cognitive tests. For those with a significant decline in mental functioning, researchers tested for dementia.

With an average follow-up of 7 years, researchers analyzed the information from 7,444 subjects ages 65 to 80. Eight hundred and two women experienced a significant drop in cognitive functioning (368 had mild cognitive impairment, and 265 developed dementia).

Scientists compared the duration of sleep for those with and without cognitive decline. After adjusting multiple social and lifestyle factors, depression, cardiovascular disease (CVD), and other clinical characteristics, the researchers discovered:

Women who reported an average of six or fewer hours of sleep had a 1.26-fold increase in the probability of a cognitive decline.

Women who reported sleeping more than eight or more hours had a 1.35-fold increase in cognitive decline probability.

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Keep in mind that this study is a so-called observational one. It does not establish causality; we do not know if sleeping too little or too much causes dementia. Still, if you have an overly short or long sleep duration, you may want to make an appointment with your primary healthcare provider.

Exercise clears debris, too

University of Rochester Medical Center scientists have been looking at the relationship between lifestyle and brain function. Using mouse models, they showed that exercise helps rid the brain of harmful debris. The study authors observed that daily running increases cerebrospinal fluid (CSF) flux in the mouse brain’s widespread areas, contributing to the pro-cognitive effects of exercise.

How exciting that researchers have identified a pathway, the glymphatic system, that may explain why we sleep. I think the discovery of the circuit brings us to a better understanding of the short sleep — memory loss connection.

What if you already have memory issues?

Aerobic exercise may slow the shrinkage of your hippocampus, a small structure in the brain that is charged the formation of new memories and is also associated with learning and emotions. Scientists at the University of Texas, Southwestern (USA) compared cognitive functioning and brain size between two groups of sedentary older adults who already had memory issues.

This study is the first randomized, controlled experiment to examine the effects of exercise on brain structure and function. It also looks at the amyloid plaque for this 55 year and older population. Here are the two groups:

  • Group #1 did aerobic exercise for approximately thirty minutes, 4 to 5 times per week.
  • Group #2 did flexibility training.

Both groups preserved their memory and problem-solving abilities. In addition, brain imaging showed:

Those in the aerobic exercise cohort with amyloid buildup had slightly less volume loss in the hippocampus. We know that this small structure deteriorates with the progression of dementia.

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The study authors speculate that aerobic activity can increase blood flow or encourage other factors that promote nerve cell growth and brain survival. Exercise may reduce the harm induced by amyloid plaques on nerve cells in the hippocampus.

Aerobic exercise can neither prevent nor cure dementia, but activities that promote blood vessel health are associated with better brain health.

“I love sleep. My life has the tendency to fall apart when I’m awake, you know?”
Ernest Hemingway

I have degrees from Harvard, Yale, and Penn. I am a radiation oncologist in the Seattle area. You may find me regularly posting at

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