The Doom of Men and the Ringwraiths

[Gorthol]

I think that the effect of prolonging the lives of mortal bearers probably came from the Elves. Remember, it was the Elves themselves who forged the Rings, not Sauron. He taught them how to do it, and probably helped them, but he didn't do it himself.

All the rings except the Three were formed through the advice and instructions of Sauron, so using his cunning he should have been able to make them *any way he wanted*.
Remember that he could have perverted them later also, before handing them out.