There are, of course, a few truly vampiric animals, including leeches, lampreys and vampire bats. And in all these cases the vampire’s intent is to draw enough blood for sustenance, but not enough to kill the host.
But what about human vampires? There are certainly many self-identified vampires who participate in gothic-inspired subcultures. Some host vampire-themed book clubs or secret bloodletting rituals; others wear capes or get vampire-fang dental implants. It’s all frightening and fun, but blood drinking is another matter entirely. The problem is that blood is toxic; because it is so rich in iron — and because the human body has difficulty excreting excess iron — anyone who consumes blood regularly runs a real risk of haemochromatosis (iron overdose), which can cause a wide variety of diseases and problems, including liver and nervous system damage.
In one form or another, vampires have been part of human culture and folklore in different forms for millennia, and the bloodsuckers show no signs of going away any time soon.