Blood is necessary for life, and it takes up a good amount of weight!
How crazy is that? 7%! Vampires would need to kill a lot of people to sustain themselves! Interestingly enough men generally have more than a woman of comparable height and weight.
In addition, people who live at high altitudes may have up to two liters more than those who live at lower altitudes. Because the air at higher altitudes has less oxygen, people who live at high altitudes need extra blood to deliver the right amount of oxygen to their lungs.
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