This is basically a theory of where the vampire myth came from, in a nutshell. Found it out after a little research.
Hundreds of years ago, people were born with a deficiency where they had to drink blood to survive. If memory serves me correctly, it was called haemobiberavitam. Around about the 1800's this deficiency was more common, and more heard of. The people who had this deficiency were pale due to this, and they were labeled 'Vampires.'
Bram Stoker then wrote a book, playing out Vampires to be something they are not, causing more misconceptions. More novels came about them, now films (damn Twilight), and so on.
Bam. The myth of Vampires.