Just to be clear, Betel leaf and Lolot (lá lốt in Vietnamese) while very closely related are not exactly the same thing, they are in the same genus but they are two different species. (the plant we get black peppercorns from is also in the same genus)
To make things even more confusing Lolot and another related plant with the latin name Piper sarmentosum are sometimes called "wild betel"
Betel is also important culturally in Vietnam (especially in traditional wedding ceremonies) but for chewing not eating at least as far as I'm aware.
So basically don't try to use true betel leaf in a recipe calling for lá lốt it won't work right.
This thread reveals a source
Paan is not simply Betel leaves. It has the areca nut inside (commonly incorrectly called a betel nut). The areca nut is a known to be highly carciogenic, causing not only oral cancers, but tumours in other locations of the body as well.
As for the betel leaf itself, I can't speak on the issue.
SE Asian has a very high rate of oral cancers, related to Paan consumption, as well as other cultural variations on the same theme.