Hi, I hopefully have some answers for you...and many of you! I also have been trying to figure out the causes of my high B12 for the past four years and after the diagnosis of a rare, genetic disease called, MEN-1 (Multiple Endocrine Neoplasia - Type 1), in early 2018 which is a form of cancer in that it causes tumors throughout my endocrine system, some are benign, some malignant, I thought I finally had the answer. Turns out I was wrong, and to date, this disease is not the cause of my high B-12. That said, I'll admit I was the slightest bit disappointed to learn this particular disease had nothing to do with my high B12...and as my health has continued to decline despite surgeries to remove tumors (the only way to battle to this disease), I have been digging even harder to find the cause of the elevated B12 knowing there IS one! I too have heard from ALL of my physicians, many of whom are quite brilliant, very well-respected, published doctors at major medical institutions such as Mayo, MD Anderson and Baylor that, "there is no clinical significance to my high B-12" when my lab reports come back! Well after four years and me requesting it be checked at least once or twice annually, (each time it has gotten a little higher...yet there's NO SIGNIFICANCE to that???!!!!) Come on already!
So here is what you need to know: Vitamins B and C are water soluble and any surplus of these vitamins is excreted in the urine. Vitamin C and all of the B vitamins -- thiamine, riboflavin, niacin, vitamin B-6, folate, vitamin B-12, biotin and pantothenic acid -- share similar characteristics because they are all water soluble. The body has a limited ability to store these vitamins so they need to be continuously replenished by the diet. Water-soluble vitamins are absorbed by the digestive tract into the blood stream, metabolized and then excreted by the kidneys in the urine.
Knowing that, here is what you need to look up, and it's right here on the MAYO website, it's on Livestrong, MD Anderson, Healthfully, WebMD, etc... Just google: "causes of high vitamin B-12 levels in the blood"
Here is what I have: a rare blood cancer called, "Polycythemia Vera"