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Is a High Level of Vitamin B12 Bad?

author image Jill Corleone, RDN, LD
Jill Corleone is a registered dietitian and health coach who has been writing and lecturing on diet and health for more than 15 years. Her work has been featured on the Huffington Post, Diabetes Self-Management and in the book "Noninvasive Mechanical Ventilation," edited by John R. Bach, M.D. Corleone holds a Bachelor of Science in nutrition.
Is a High Level of Vitamin B12 Bad?
Animal products are the primary source of vitamin B12 in the diet. Photo Credit Thomas Northcut/Digital Vision/Getty Images

Vitamin B12 is an essential water-soluble vitamin. Adequate intakes of vitamin B12 are necessary for the production of red blood cells and to prevent anemia. Vitamin B12 is also important for neurological function and the synthesis of your DNA. A vitamin B12 blood test is most often performed to test for deficiencies. However, elevated blood levels of vitamin B12 may be a sign of liver disease or certain types of leukemia.

Vitamin B12 Test

The vitamin B12 test is a blood test to determine your blood levels of vitamin B12. Folate, another B vitamin, is also tested at the same time. The test is performed to assess if you have megaloblastic anemia, a condition in which you have abnormally large and immature red blood cells that are unable to carry oxygen throughout your body. Vitamin B12 levels may also be tested if you are suffering from neurological changes such as dementia. Normally the test is looking for low blood levels of vitamin B12.

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As a water-soluble vitamin, toxicities of vitamin B12 are rare. Any vitamin B12 consumed in excess is excreted in your urine. No adverse effects have been reported with excessive consumption of vitamin B12 from either food or supplements, according to the Office of Dietary Supplements. In addition, the Institute of Medicine, the establishment that determines daily vitamin recommendations, has not set an upper tolerable limit for vitamin B12. If your blood levels of vitamin B12 are greater than normal, more than 835 picograms per milliliter, it may be a sign that you are suffering from a type of liver disease or leukemia.

Liver Disease

High blood levels of vitamin B12 may be a sign of cirrhosis or hepatits infection. Further tests are necessary to diagnose the problem. Hepatitis is a condition that causes inflammation of your liver, impairing its ability to process nutrients. It is usually caused by a virus, but alcohol abuse and certain medications can also cause hepatitis. Cirrhosis is a serious condition characterized by continued inflammation and scarring of your liver tissue. Alcohol abuse and hepatitis are the most common causes of cirrhosis.


Like liver disease, an elevated vitamin B12 level cannot adequately provide a diagnosis of leukemia. But it may indicate the need for further testing. Leukemia is a type of cancer in which white blood cells are higher than normal in either your blood or bone marrow. It also causes a reduction in red blood cells and platelets, cells needed for clotting blood. Types of leukemia include acute lymphoblastic, acute myelogenous, chronic lymphocytic and chronic myelogenous. The exact type of leukemia is determined by a doctor looking at cells under a microscope.

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