This linked BBC article asks the question “Could I live as a vampire by just drinking blood?” I’ll save you the trouble of reading it if you really don’t want to, and just answer the question for you. No. You cannot. Unless you are a *real* vampire, in which case you would already be “dead” in the clinical sense. You would have no heartbeat.
The article goes into detail, though, explaining why you could not subsist on blood. The amount of it you’d have to drink to avoid nutritional deficiency would lead you in no short time to death by hypertension and/or kidney failure. Animals that survive by drinking blood have specialized digestive systems that humans do not. And, being undead, vampires need not worry about blood pressure or renal failure. If you are a supernatural being, you’re good to drink as much blood as you desire. If, however, you are a human being who likes to pretend to be a supernatural creature, drinking too much blood is gonna kill you, and sooner rather than later.
What about sanguinarians, then? Human beings who claim to need to consume blood to maintain their health? I have the testimony of people whom I know and trust to assure me that this need is real. But they use blood as a supplement to their diets. None of them is trying to live on it exclusively.
