Almost all vampire tales have an underlying common theme. One that hasn't even been touched by this Wiki. The question of how vampires survive off blood remains a mystery that I intend to tackle in this Vampedia post, along with all others throughout the class.
Consumption Methods of Blood: Edit
One of the most common methods of blood consumption is by biting the living person and using the fangs to simply pierce the skin. According to National Geographic vampire bats bite their prey then use their tongue to drink the blood. This occurs because the vampire bats tongue contains an enzyme that acts as a blood anticoagulant. Meaning, that it prevents the blood cells from clotting together to close the wound, and allows the bats to drink more blood. This consumption method is most common, and can be seen in almost any vampire folklore. In one of the vampire short stories called "Bucket Of Blood" the vampire is seen as draining the blood into a bucket, then drinking out of the bucket. While there may be other consumption methods of blood, these are the main two I wanted to discuss.
Amount of Blood: Edit
The average adult human contains 4.7-5.5 liters of blood, whereas a child will contain roughly half of that (1). In this post, I will be using the value of 5.5 liters of blood for an adult when discussing nutritional values. However please note that in some instances, vampires will not drink all the blood from a human, as seen in Buffy the Vampire Slayer Season 5 Episode 1.
Blood Contents: Edit
Blood contains a plethora of nutrients, however it would take much too long to analyze every aspect of blood, so for this initial post I will be focusing on the iron, vitamin C, and salt (4).
|Nutrient||Amount in Blood per Liter||Amount Required to Live|
At first glance at this table, one would expect the answer to be yes, it is possible for a vampire to survive off of blood. However, there are a couple of issues. The first, is that by drinking blood, you will consume far too much iron, a substance that the body has a hard time excreting. The same National Geographic article discusses how vampire bats combat this by having a membranous layer in the G.I tract to prevent too much iron from entering their own blood stream. As for Vitamin C, you'd have to drink 9 liters of blood to meet that requirement everyday, unless you had the human consume a lemon before drinking the blood, in which case the value of 5mg per liter goes to 15mg (Life Science Article). Finally, you would also have high sodium levels, which will lead to quicker dehydration, however it is possible to combat this with water. Blood on average contains 700 kcal/liter, which is 3850 kcal total in an adult. Based on that value alone it is possible for Vampires to survive off of blood, since the required kcal per day for an adult is 2500kcal (2).
With all of this data acquired from a plethora of external sources, my final conclusion is that it is not possible for a Vampire to survive off of blood alone based on the current vampire description found in most folklore. However, if vampires are capable of consuming water, or other things in addition to the blood, it would be possible.