Consistently elevated blood sugar, inflammatory pufas and a generally toxic system causes arteries to harden and lose their suppleness. the extremities are the first thing to go. It isn't to be joked about but..
It happened to a friend...he took powdered rhino horn for a month which worked but every time he got a hard-on he started head butting land rovers.
My grandad was in a nursing home and they gave him viagra, he didn't want sex but it stopped him from rolling out of bed.