Elevated B12 does not cause anything that has been reported as yet.

However, in a person who is NOT taking vitamins, or eating enriched foods, having a high B12 level (over 900) can be a signal of some disease states. B12 does not cause these, but happens to be a result. And this is pretty rare.

A test result over 1000 when one is taking supplements of B12 is not a reason to stop taking it.

Some cancers, kidney disease, and excessive bacteria in the bowel may raise B12 levels.

If you were taking vitamins containing folic acid and B12 when that test was taken, your levels will reflect that, however.

Doctors don't understand B12, and because the results are flagged at the lab, they respond as if it were any old other flag that signals harm. They are creatures of habit, in other words.

What your doctor should say is this: "I see your B12 levels are high. Do you take supplements/vitamins? If the answer is NO, then we need to further test you to see why this level is high."

Some people need more B12 than others. The folate is a whole other story. In people who cannot methylate folic acid to methylfolate which is the active form, folic acid levels may test artificially high. It might mean you have a DNA error of metabolism called the MTHFR polymorphism, and that should be tested for then. Foods in US are now fortified with folic acid (which is synthetic and not natural), so if you consume them your folic acid level may show high. This is controversial at this time, since the food fortification is rather new.