What about the compound effects of a sleep surplus?
I sleep 9 hours a night, sometimes slightly more, and I often worry that I might have conditioned my body into accepting more sleep than it needs - with potentially negative long-term consequences. But when I sleep less I feel off. I think of the quantitative length of my sleep as offsetting the qualitative hit it suffers from my daily caffeine.
I think there are negative correlations with excessive sleep and mortality/health. But I doubt there is causality. As in it is much more likely that people who are of poor mental/physical health will sleep more, rather than your health deteriorating because you are sleeping +1 hour than the accepted norm.
I wouldn't worry too much, it is an absolute blessing that you have the conditions and the body to sustain 9h sleep cycles. As a father of two, with copious amounts of caffeine intake, I wouldn't mind having some nights with that quality of sleep myself! :)
I sleep 9 hours a night, sometimes slightly more, and I often worry that I might have conditioned my body into accepting more sleep than it needs - with potentially negative long-term consequences. But when I sleep less I feel off. I think of the quantitative length of my sleep as offsetting the qualitative hit it suffers from my daily caffeine.