I have a historian standing next to me right now who says the lead poisoning story is BS and people who propagate it should be shot/severely eye-rolled at. He says that:

-Romans did drink lead-sweetened wine but
-only lower class romans did so because they could not afford better
-lead-sweetened wine continued to be drunk up until the 18th century
-While some people undoubtedly died, saying it caused the fall of the Roman Empire is a ridiculous just-so story
-particularly because the sweetener was used centuries before and after the fall with no increasing usage leading up to the fall
-and the eastern Roman empire continued to exist for another thousand years anyway.