These sleep habits can destroy your brain

Dr. Frank Shallenberger, MD

March 15, 2021


Does your sleep play a role in your risk for Alzheimer’s and other forms of dementia? Two recent studies say yes. But the results may surprise you.

When you add up the findings of the studies, it looks like the amount of sleep you get is not the determining factor for your future brain function.

These studies showed that there’s something else about sleep that’s more important.

The first study, called The Nurses’ Health Study, simply looked at the amount of sleep a person gets, and whether that can determine their risk of dementia. These researchers studied over 15,000 women. All of them were older than 70. They all completed a battery of six different cognitive tests to determine their mental status.

Over the next six years, they repeated the tests three more times. Then they compared the results of the test scores to how much sleep each woman was getting. Here’s what they found.

Women sleeping an average of seven hours a night maintained the best scores. The women who slept less than five hours per night on average had the worst scores.

The women who slept an average of nine or more hours also had lower scores. But they were still about 50% better than those who only got five hours.
So it’s apparent that sleep is an important determinant of the risk for brain deterioration.

But There’s More to This Story

The second study is referred to as the “Three City French Study.” In this study, the researchers looked at 4,900 men and women who were 65 or older in the cities of Bordeaux, Lyon, and Montpellier.

The researchers followed the participants for 10 years with periodic cognitive testing using the Mini-Mental State Examination. This is the test that I use in my practice. It’s an excellent way to monitor brain function and any potential tendency to dementia.

They also questioned the participants regarding the quality of their sleep. Specifically, did they have trouble falling asleep and/or staying asleep? They also asked them to rate their overall sleep quality and to count the number of recent insomnia episodes.

And finally, they asked if they felt excessively sleepy during the day. This is a very reliable study because of three important factors: It included a large number of people. It followed them over a long time. And it used an excellent cognitive testing method. So what did they find?

Interestingly, the results of the Three City study do not completely agree with those of the Nurses’ Health study. But they do serve to clarify just what may be the defining issue in the relationship between sleep and brain function.

And it doesn’t look like how much sleep you get is the deciding factor.

The Results of the Study Were Surprising

The results showed that not all sleep problems lead to brain decline. These included problems with falling asleep and early morning awakenings. In fact, on average, those who reported frequent insomnia and difficulty staying asleep were 20% less likely to have cognitive decline than the better sleepers!

There was only one factor in this study that was consistently associated with cognitive decline. And that was daytime sleepiness.

Those who reported sleepiness during the day were about 25% more likely to develop brain decline than those who did not feel sleepy during the day. This was true even for those who had insomnia or restless sleep. As long as they were not sleepy during the day, they had no decrease in brain function.

So what explains these apparently different findings? It has to do with sleep stages.

How many times have you had what you would call a rough night and yet were surprised to see how well you did the following day? It happens commonly.

Sometimes I am awakened in the middle of the night by a phone call from a patient in distress. And often enough, I can’t get back to sleep. So I just lay there for the next three to four hours and ponder how bad the next day is going to be. And yet many times, even though I got only four to five hours of sleep, I slam through the day like everything was perfect.

On the other hand, how about those nights when you seemed to have slept very well and yet you still felt sleepy the next day? These effects are not determined by how much sleep you got, but how deeply you slept when you were asleep.

Here’s How It Works

There are four stages of sleep. The first two are the lighter stages. In these stages you can be fairly easily wakened by a sound. The second two stages are the deeper stages. When you are in these stages, even a fairly loud noise will not wake you up. It’s in these stages of sleep that the restorative part of sleep happens.

In 2002, a study published out of Johns Hopkins Medical School was able to show that being sleepy in the day is strictly a matter of whether or not there was a disturbance in the deeper stages of sleep. When something disturbs the lighter stages of sleep, there is no sleepiness during the day. And this is what ties the results of the Three City and the Nurses’ Health studies together.

It’s not how much sleep you get that is important. What’s important is how much time you spend in the deeper stages of sleep.

If you sleep only five hours, but 20% of your sleep is in the deep stages, you had one hour of deep-stage sleep. On the other hand, if you slept a full eight hours, but only 10% of that was deep stage, then you had 48 minutes of deep sleep — 20% less than on your five-hour night.

The most damaging effects of sleep deprivation on your brain are not from too little sleep as the Three City study shows. They are from too little deep sleep. Deep sleep is when the body repairs itself and builds up energy for the day ahead. And it plays a major role in maintaining overall health and brain function.

How to Get a Higher Percentage of Deep Sleep

The best plan for deep sleep is to make yourself younger. Men and women in their 20s spend about 20% of their sleep in deep sleep. But by the time they are 50, that is cut in half to 10%.

So what’s the easiest way to get younger? Two things I have discussed many times before. Get in shape, and make sure your hormone levels are youthful.

A regular and properly done exercise program increases the percentage of deep sleep. The best exercise program is one I’ve discussed many times in these pages. You can read all about it on my website or you can read Al Sear’s book, PACE: Rediscover Your Native Fitness. Then take the time and make sure you’re in tiptop shape.

Also, supplementing with the right dose of bio-identical hormones – testosterone in men and estrogen and progesterone in women – increases deep sleep. You will need a doctor familiar with bio-identical hormone replacement to help you with this. You can find one at

What About the Sleep Hormone?

One of the most important hormones for deep sleep is melatonin. You don’t need a doctor to get this one. You can find it at any drugstore or pharmacy. Everyone over the age of 50, no matter how well they sleep should take 1 mg of melatonin for every pound of body weight before they go to sleep.

Research is showing that melatonin acts on special brain receptors called MT2. These receptors specifically induce deep sleep. Young people have much higher levels of melatonin, which is no doubt responsible for their increased levels of deep sleep.

Avoid drinking alcohol before bed. It will suppress deep sleep. So will many medications, including statins and antidepressants.

Lastly, take the amino acid tryptophan. Tryptophan is the source of the brain chemical serotonin. And serotonin is critical for deep sleep. I find that almost everybody over the age of 50 is lacking enough serotonin. This is especially true of women. A good starting dose for men is 500 mg before bedtime. Women should take 1,000 mg.

As an alternative, you can take 5-HTP. 5-HTP is the activated form of tryptophan, and as such is often more effective. You don’t need as high a dose when using 5-HTP — 50 mg for men, and 100 mg for women.

If you do not have daytime sleepiness, then perhaps you are already getting enough deep sleep. The Three City study shows that this is the main symptom we should focus on. But if you find yourself reaching for that Starbucks a little too often, perhaps you should work on increasing the amount of deep sleep you get. Your brain will thank you later on.


Berr, C., et al. “Sleep and cognitive decline in the elderly: The French Three-City cohort” AAIC 2012; Abstract F2-03.

DeVore, E., et al. “Sleep duration and cognitive function: The Nurses’ Health Study,” AAIC 2012; Abstract F2-03-01.

Gever, John. “Bad Sleep Tied to Cognitive Decline,” MedPage Today. Published: July 19, 2012.

Punjabi, N.M., et al. “Sleep-Disordered Breathing and Daytime Sleepiness. Sleep, vol. 25, no. 3, 2002, 314.

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