You assume a vampire needs as much of the D as you or me
Do bats need vitamin D?
Most bats, especially nocturnal ones that roost in dark places, have low vitamin D levels because they lack exposure to sunlight and often consume diets low in vitamin D.
You missed the entire point. (Because ofc you have)
Op entire argument was that vampires rely on blood for vitamin D. Which is a ridiculous notion after I demonstrated it's like squeezing water out of a rock. Even if hypothetically vampires required smaller amount than humans then it would still be incredibly inefficient source for vitamin D.
Put the fries in the bag.