A diet of too much corn, and not enough everything else, can give you the condition that inspired vampire legends. Learn about the corn-fed vampires who stalked the American west at the turn of the last century.
Corn has proved itself to be very useful. Over the last century, people have learned to use it to feed themselves, make all sorts of food additives, turn it into a building material, and even make it into biofuel. But first they had to learn to mix it with a few things, or they would turn into vampires.
Or, at least it would turn Europeans into vampires. Corn was an American food, and the native Americans knew to mix lime into their corn when they prepared it. European settlers started raising, and living on, mostly corn, and as it made its way around Europe and became the food of the poor, but they didn't add the lime. Without the lime - calcium hydroxide - or without specific types of amino acids, things start going bad. Corn contains niacin in an indigestible form. This isn't a problem for occasional corn-eaters, but people who make it a staple suffer from niacin deficiency, and from pellagra, the condition that comes with it.
Pellagra victims erupt into blisters when their skin is exposed to the sun. They stop being able to digest normal foods. Their tongues turn dark red, making them look like they've been sipping blood. They start staying up nights - not because of some latent vampirism but because most of them develop severe dementia. The dementia is also associated with aggression. Pellagra also tends to bring on diarrhea, which isn't part of most vampire legends, but other signs are there.
Vampire legends go back longer than corn in the old world, but this resurgence of symptoms which happened every year in spring, when supplies were dwindling and people ate mostly cornmeal, may have inspired new vampire legends. Into the early 1900s, people hadn't been able to pin down the source of the condition, and though it must have something to do with mold that grew on corn. It wasn't until 1937, when it was discovered that niacin in vitamin form cued pellagra in dogs that people finally got wise to it all. Today niacin supplements are often given out to people and animals who feed mostly on corn, and vampire numbers have been reduced. We get enough of them in pop culture, anyway.