Sleeping longer than 6.5 hours a night associated with cognitive decline in the elderly?

“Sleeping longer than 6.5 hours a night associated with cognitive decline [in the elderly] according to research – what’s really going on here?”

A good night’s sleep is important for many reasons. It helps our body repair itself and function as it should, and is linked to better mental health and lower risk of many health conditions – including heart disease and diabetes. It’s also been shown that not getting enough sleep is linked to cognitive decline and conditions such as Alzheimer’s disease.

But more isn’t always better, as one recent study found. Researchers from the Washington University School of Medicine have published a paper that indicates that just like getting too little sleep, sleeping too much may also be linked with cognitive decline.

Full article:


Maybe the title of the article should also state “in the elderly,” seeing how all the test subjects were in their mid 70s


Very interesting. I hope researchers can figure out the implications of their findings with more certainty.

In the meantime, I won’t encourage my elderly parents to sleep less than 7.5 hours (not that I have any influence in the matter) since this study doesn’t seem to have a strong explanation for these results.

As I think about it, I wonder if they considered whether elderly people might habitually sleep in stages. Perhaps two sleeping sessions overnight, or otherwise over a 24 hour period—or by napping during the day.


Why don’t you read the original paper than instead of some article about the study…


Excellent idea. A little bed time reading.


Not sure about that, I mean from the abstract alone…

To test this hypothesis, we monitored sleep-wake activity over 4–6 nights in 100 participants who underwent standardized cognitive testing longitudinally, APOE genotyping, and measurement of Alzheimer’s disease biomarkers, total tau and amyloid-β42 in the CSF.

I could argue the whole thing the other way around and say “people with cognitive decline sleep less”… correlation is not causation, so if you test 100 subjects over 4-6 nights, I don’t think you’d have enough data points to argue either:

  • less sleep causes cognitive decline
  • cognitive decline causes less sleep

…or do you think that you can actually measure a decline over the span of 4-6 days?

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“…more than 6.5 hours every night had a greater risk of cognitive decline.”

If I sleep less than 6.5 hours for a week I die, the cognitive decline is irrelevant…


@Liam are you also in your mid 70s? Because if you’re not… that study is about as relevant to you as postnatal depression studies are to men or prostate cancer studies are to women.

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I see. I am still some decades away from that!

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This is what I was about to reply, and even if there is causation, the extend of it is not discussed.

Lets assume sleep deprivation causes the release of the biomarkers

Now, lets assume the released biomarkers cause two things: longer sleep and decreased mental function.

This eliminates the long sleep - decreased mental function link as a causality, but gives them both the same cause. Which seems more likely to me than to say that longer sleep causes decreased mental function.

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…or in science parlance “test our hypothesis” :wink:

which could of course be a separate study. You also have studies that have shown that during sleep your brain cleans out the amyloid-beta plaque that builds up during the day. So you could the other way around argue:

…lack of sleep prevents amyloid beta plaque to be removed completely. But who is to say that the whole thing is not simply an issue of recreational drugs such as alcohol or simply a melatonin issue or maybe 4-6 days was not enough to adjust to the environment and some people just couldn’t sleep well in a hospital environment and their lower performance was therefore acute and not chronic because they got less sleep than at home.

Good point. I think what most people fail to understand when they claim that “science has shown” or worse “science has proven” is that it’s just a matter of having a hypothesis, testing it, and then interpreting the results. That’s what science is.

Even the true-ism of 1+1 is 2 and not 3 is only true because you already assume that you are not working in binary, because there 1+1 is 10.

That’s hopeful. Of course it depends on the odds that you can go decades without a fatal week of less than 6.5 hours of sleep.


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If we’re comparing too little sleep with too much sleep, I find actually perform better in Memory Sports on less sleep than more. I’m not sure why this is. But during a stretch earlier this year when I was getting a lot of sleep, I felt more foggy and slow mentally, it was bizarre. I have an optimal sweet spot for sleep and memory sports, which I think is around 6.5-7 (7.5 max I think). If I get close to 8 or more, then that’s when things go south for me I find. I don’t have too many chances to sleep this much with young kids, so maybe my body and mind would adapt to it over time. Who knows.

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So I think it has to do with the mentality.

If go-go adrenaline-filled ready2go for action, then that 6-6.5 hours of sleep might be accurate.

If sleepy, love-sleeping, love-chilling, then I’m not sure if it mixes. Because I will be sleepy.

I mean if I’m focusing diligently, the sleepiness goes away. I can get away with 6hrs.

If I’m not focusing diligently, then 6hrs will make me crave sleep because I’m in chill-mode.

I mean, am I being casual or not casual. I’m not sure but I think eventually I want to snooze. Suppose I’m go-go-go attentive focusing, 6hrs-per-night-diligent-work-mode. That will work for many days, but I’m afraid that, after a week (?) I will probably crave sleeping a huge amount of sleep, and that might interrupt my groove of balance. I’d rather go for something like a steady 7.5 and not risk wanting to snooze hard sometimes.

Can I truly be at peak-performance if I chronically feel sleepy? Like, driving a car, I’m supposedly at a lower risk of cognitive decline but… what? I could doze off and crash.

My understanding is that we tend to sleep in cycles of roughly 90 minutes. (With variability by individual, of course).

It seems to me possible that finishing a cycle may be as important as—or even more important than—meeting some overall duration of sleep.

As much asI personally seem to function better after sleeping around 7 1/2 to 8 hours, waking up at the wrong stage of sleep also seems to affect me a great deal.

A recent study actually found that despite the elevated levels of Alzheimer markers, some individuals showed no sign of cognitive impairment.

I’m going to just advocate my Art of Memory forum post about the article :stuck_out_tongue: Research article: Cognitive Function Trajectories in Centenarians (100-102 year olds)

After their deaths, forty-four of the participants underwent autopsies to measure the plaques, or tangles of protein, in their brains that are typical markers of Alzheimer’s disease. Although many participants had the brain plaques typical of people who develop Alzheimer’s disease, none of them showed signs of disease itself. In addition, participants with the genes linked to an elevated risk of developing Alzheimer’s disease showed no signs of [cognitive decline].

And while the age in the book “Why we Sleep” by Matthew Walker is not mentioned, the book mentions that nothing indicated anything bad would happen about sleeping “too much”. Perhaps other than the obvious - you have less wakeful hours and consequently less time to be physically active and less time to be cognitive active.
On the contrary, everything bad happens when sleep deprived. Which by the way has an accumulative effect! :open_mouth:

So I’m pretty sure, when I do turn 70++, I will continue to sleep slightly more than 6.5 hours. Alas, I may sleep half at night and half during the day, though I will get my sleep! :smiley:

Though, 6-6.5 hours seem to be quite okay for me when it is summer or just that there is enough sunshine hours. During winter times my body does tending to require more sleep (7-8 hours).

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I agree nothing bad can happen from sleeping too much. There was a controversial study released a few years ago suggesting that people who sleep for a longer period of time die sooner as well, however it was heavily criticized for not allowing for the fact that people who sleep a lot longer than normal usually have other health problems. I would say almost with certainty this is the case here. If you need to sleep a really long time, you’re likely not the healthiest individual for one or another reason.


The researcher would have his study, but I guess everyone has a different lifestyle, eating habits and sleeping habits. So it is completely upon person what suits them. I generally need 7.5 hours of sleep daily; however, I am not 70+ yet, but age will not reflect on my this habits.