QUOTE(SubRosa @ Jun 9 2012, 11:30 AM)

I would not be surprised. Vampires are undead after all. Other forms of undead do not need sustenance. Vampires are kind of the odd man out in a way, in that they feed on people. But I do not think Bethesda ever really explained why they feed. Except of course that it seems to suppress the vampiric disease, reducing their powers and making them appear more 'normal'. So feeding on people only seems necessary for vampires that want to blend in. Otherwise it is better to just abstain and be more powerful.
I have thought feeding on blood is like an instinct for vampires, or like a drug. Maybe both.