I honestly don't think Jon is as healthy as his looks would indicate. He's made a comment in an interview to the effect that he prays a lot every day because it " soothes" him but the only thing he ever asks for for himself is good health. People generally don't pray for things they have/ take for granted. Then he commented that the band would tour if everyone was healthy enough to do so.

I believe he's giving all he's got to give.