Caffeine consumption does lead to poor sleep.

Makes sense then that lots of coffee would lead to many nights of low quality sleep thereby increasing the risk of all sorts of bad health outcomes

I suspect it's the other way around, or a cyclical effect. Plenty of people simply do not allow themselves a full night of sleep, or feel that they cannot afford a full night of sleep (e.g. working 2 jobs & raising kids), leading to dependence on caffeine for functioning.

Yeah it’s probably some kind of feedback loop. Over time the loop leads to more and more caffeine consumption and worse and worse sleep.

I can tell you from personal experience it’s not a good thing to have happen to you. Once I reduced my coffee intake to 0 cups a day my sleep became so happy and blissful.

Alas I’m back to drinking 1-2 cups a day. I hope I never go back to that feedback loop so I make sure to only drink coffee in the morning or early afternoon. Never later on in the day.

The problem with caffeine is not only the length of sleep but also that it negatively effects the quality of sleep.

So you not only sleep less hours but those hours won’t be as effective for the body and brain.

Doesn't coffee impact sleep quality as well? At 6 cups a day, I'd expect some caffeine left in the body when sleeping.

Twelve hours to metabolize. The six cup people are totally jacked.

Half-life of six hours, so after twelve hours, one quarter of the caffiene will still be in the blood.

Tolerance kicks in. I can drink a double espresso after a dinner and still sleep like an angel.

Perhaps, but do you really know if and how much REM sleep you are getting? I've seen some things that link dementia more specifically to quality of sleep and REM time.