Agreed that paywalls - and the constraints in writing an abstract are a definite issue.

But "6 cups a day", no matter the size or caffeine content, says "poor sleep", particularly poor sleep in the beginning of the evening when the preponderance or NREM3 occurs would seem to be the issue as short sleep, particularly short NREM3 has been linked to dementia.

They didn't mention sleep in the abstract; was it in the paper itself?