[macrael]

From the public results only[1] (I don't have a copy of the whole study) they studied the following things looking for correlation with brain decline:

* short sleep duration

* sleep quality

* difficulty initiating sleep (DIS)

* difficulty maintaining sleep (DMS)

* early morning awakening (EMA)

* daytime sleepiness

They only found that the middle four were correlated. I don't know what exactly "sleep quality" is but the others are pretty easy to understand. And the point is that the duration of a person's sleep is not what mattered, it was the quality.

[1]: https://www.neurology.org/doi/10.1212/WNL.0000000000209988

[timr]

Also, worth saying: these things were based on self-reported data, which is basically crap.

>To estimate the effects of sleep quality on the brain, the researchers surveyed approximately 600 adults on how well they slept. The participants were asked the same questions five years later and underwent brain scans 10 years after this.

This is press-release science. Maybe the latter three things you can remember, but I have sensors and whatnot in a fancypants mattress (i.e. I'm highly motivated to know), and my subjective opinion of my prior night's sleep is pretty uncorrelated with what they say. I couldn't begin to tell you the quality of my sleep from a week ago.

[fsckboy]

self-reported data is basically crap as it regards actual sleep patterns, but it could (hypothetically) be a rock solid predictor of brain shrinkage

[timr]

You can't just take crap data and compare it to a hard outcome and claim victory if you find a correlation.

Crap data is crap, no matter what you compare it to.

[fsckboy]

you're wrong. The only evidence we have for gravity is the correlation of mass and attraction. The theory of gravity does not contain any hint of a reason why, it simply points out what we can observe. Correlation is the only evidence we have.

And you have not ruled out that complaining about sleep in various ways isn't a direct side effect of brain shrinkage so the hypothesis remains open.

[digging]

Sleep quality, if excluding DIS, DMS, EMA, usually will refer to things like apneas, nasal congestion, digestion, noise or light in the room, etc. Disturbances that don't wake the person but do tax the brain.

[derefr]

I would describe low sleep quality as "difficulty entering or maintaining the restorative phases of sleep." It's the thing a sleep clinic measures with an EEG.