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Oncology (General Cancer)/elevated b12 levels area of concern?


QUESTION: Dear Doctor,

First off thank you for taking the time to read my question.  I'll make it short.  I was taking a b12 suppliment for an undiagnosed neuropathy.  Seemed to help.  Taking it daily for several months.

Fast forward to last month my doctor thought based on my symptoms I could be deficient.  Did a blood test.  My B12 came back at 2000+.  Was instructed to discontinue all vitamins and recheck.  A month later rechecked and came back at 1700.  All other basic metabolic labs etc appear normal.

Google is my worst enemy - and I made the mistake of searching high b12 and one concern is blood cancers.  My mother died of Myeloma, her grandfather had some type of blood cancer

Question:  Could daily supplimentation create such high levels and as a specialist would you be concerned with these levels if I were your patient with knowledge that I did orally suppliment with b12?

Thank you kindly if you are still with me.
Kind regards

ANSWER: First of all, it's not uncommon for someone on supplements to have a high B12 level.  The vitamin is stored in the liver, and if someone stops absorbing B12 from the diet because of a nutritional deficiency or because of the failure of the gut to absorb it, clinical signs of deficiency don't show up for several years. (The liver holds a lot of b12).  High doses of B12 (at least in the range you've described) don't cause adverse symptoms.  Certain blood disorders are associated with elevated b12 levels.  However, if your blood numbers are normal, I don't think I would do anything at present; when the blood is normal, and you have a high b12, you probably don't have a blood disorder.  I would bet that after a year or so, your B12 will be down even more if you stop taking extra.  On the other hand, if it appears to help your neuropathy, and the neuropathy starts to get worse after you've been off it a while, I'd probably start it up again.  Hope this helps.  

---------- FOLLOW-UP ----------

QUESTION: Dear Dr. Higby,

Thank you again for taking your time to respond.  I am very appreciative.  You put my mind at ease.  May I ask just out of curiosity what you look for in other blood work such as CBC that would be indicitive of concern in terms of blood cancers?  I have always been interested in this topic.

Thank you kindly and have a wonderful afternoon.


Generally you look at some measure of the total numbers of red cells, white cells, and platelets; you would want to know the percentages of different kinds of white cells; and you would want to know the predominant size and shape of red cells, together with a measure of variation.  In addition, good hematology technicians examine a blood smear through a microscope to see if there are any visual abnormalities not picked up by the automated screen which gives the numbers above.  If all of this falls in the normal range, you don't really have a blood disorder.  

Oncology (General Cancer)

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Donald Higby, M.D.


I can answer almost all questions related to the treatment and natural course of most kinds of cancer, especially cancers of prostate, colon, lung and breast.


I have been a practicing medical oncologist for 36 years, and have been chief of service at a major medical center for 25 years. I've also done research in cancer treatments.

American Society of Clinical Oncology

New England Journal of Medicine American Journal of Medicine Journal of the American Society of Clinical Oncology Hematology Transfusion Medicine

MD, Stanford University Internal Medicine residency, St. Louis University School of Medicine, St. Louis, MO Medical Oncology Fellowship, Roswell Park Cancer Institute, Buffalo, NY

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America's Best Physicians, last 14 years

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