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How much blood does a vampire need?

Could a humanesque creature derive all its nutrients from drinking blood?

Both these questions have some good answers and my question is based off them both...

  • Would there be a difference for the type of blood, such as if a vampire drank AB+ blood, would he gain something more then if he drank O+ blood.
  • What about negative blood?
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  • $\begingroup$ In your scenario, are the vampires incorporating the blood into theirs through some fantasy fusion process, or are they just drinking it? If it's the latter, it will have no effect at all, because any blood can be digested by anyone (obviously not as much as a vampire haha). $\endgroup$ – Mikey Jan 2 '16 at 21:46
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The simple answer is no, not in any meaningful way.

If you read this article: http://www.todayifoundout.com/index.php/2013/06/how-blood-works-and-the-difference-between-blood-types/

It gives a good introduction to blood types.

There are 8 main types of blood separated into 4 groups. The groups are A, B, AB, and O. They are grouped together by the presence or absence of what is known as an antigen. Antigens are substances within the blood that cause our immune systems to create antibodies. These antibodies then kill anything the immune system thinks is a threat. The specific antigens that create the different blood types are found on the surface of red blood cells and are known as type A and type B. They’re further separated by the presence of another type of antigen known as rH factor. If you have this rH antigen present, you’re considered positive, if not, you’re considered negative. Someone that has type A antigens and rH factor is considered to have type A+ blood. If you have both types of antigens and no rH factor, you have type AB- blood. If you have no A or B antigens then you are type O blood.

All of this matters because of those antibodies your immune system creates. Someone with type A blood will have antibodies for type B, and someone with type B will have antibodies for type A. Type O has antibodies for both A and B. If you were to give type B blood to someone who was type A, their antibodies would attack the type A red blood cells causing very unwanted side effects, including possible death!

As you can see from this description the only difference is in antigens within the blood that identify it as being yours or not. These are too small to have any nutritional effect.

The only way blood type may be significant is if the vampires are somehow susceptible to or need those antigens. For example if a vampire has recently drunk blood of one type and then drinks another the white blood cells from the first may fight the antigens from the second. If they are directly using the blood in their systems then they would need it to be compatible with their own antigens.

This is unlikely though as most digestive processes are going to break down the antigens and you would expect vampires to evolve the ability to process any blood group.

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  • $\begingroup$ so, what your saying is that a vampire's eventual evolution would give them the ability to strip the blood of it's type, so that it wouldn't effect them. huh....that just raises more questions. thank you very much. $\endgroup$ – Rayne Thomas Jan 2 '16 at 12:09
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    $\begingroup$ Well, the type is unlikely to affect them in the first place, but depending on what they are doing with it then it might. If it does then only being able to feed from X% of your potential prey is a severe limitation so you'd expect strong evolutionary pressure to overcome it. $\endgroup$ – Tim B Jan 2 '16 at 13:33
  • $\begingroup$ What is definitely true is that there is no nutritional difference. $\endgroup$ – Tim B Jan 2 '16 at 13:33
  • $\begingroup$ ok. that is very helpful. um... what about the "flavored bloods"? wouldn't vampires become attracted to a specified scent of blood? can blood have a scent. metallic yes, but anything else? $\endgroup$ – Rayne Thomas Jan 2 '16 at 13:41
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    $\begingroup$ As a supplement to this, one can always say "You know what, I declare the different blood types to be different for my vampires." After all, they're missing most of the hardware needed to do the chemistry, so its mostly magic anyway. Tim B's answer is the correct one, from a biology perspective, but I do encourage world builders to stretch out into whatever makes the story interesting (just know that you won't be able to make a good scientific explanation for it, if you needed one) $\endgroup$ – Cort Ammon Jan 2 '16 at 17:04

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