Vitamin B12

The A-B-C's of Vitamin Supplements

Peer Reviewed

Vitamin B12 may be taken to help prevent anemia. It assists folic acid (vitamin B9) in regulating the formation of red blood cells, and aids the body utilize iron. Vitamin B12 is also needed for proper digestion, food absorption, metabolizing carbohydrates and fats. It helps in cell formation and cell longevity.
 Vitamin B 12 element in a word cloudA disease termed pernicious anemia results if the body does not receive sufficient amounts of vitamin B12, also known as cobalamin. Pernicious anemia can be a progressive disease that disrupts maturation of red blood cells in bone marrow. The red blood cells do not receive enough oxygen and the nervous system is affected.

Symptoms of pernicious anemia may include extreme weakness, burning and/or tingling in the extremities, weight loss, confusion, memory loss, and balance difficulties. Pernicious anemia may affect elderly persons because aging may cause an inability to absorb enough vitamin B12 from foods eaten.

Dosage Guidelines

  • Adults - 2.0 mcg
  • Pregnant Women - 2.2 mcg
  • Women Breastfeeding - 2.6 mcg
  • Children - Consult a medical professional prior to giving a child Vitamin B12
  • Elderly - Consult a medical professional to determine the correct dosage. The adult dosage may not be suitable.

Sources of Vitamin B12
Vitamin B12 is found in milk, eggs, fish, cheese, and animal protein. Liver and kidney are good sources for this nutrient.

The man-made form of vitamin B12 may be labeled as cyanocobalamin. It is available in multivitamins or as B-complex in tablet, soft gel, chewable, liquid drops, and in lozenge form.


  • Generally nontoxic.
  • Patients with hyperglycemia (high blood sugar) should talk with their treating doctor as some prescription medications may interfere with vitamin B12 absorption.
  • Antigout medications, anticoagulant drugs and potassium supplements may block the absorption of vitamin B12 in the digestive tract.
  • Because vitamin B12 is found almost exclusively in animal tissues, people who have followed a vegetarian diet for more than five years should have B12 blood levels measured annually.

Disclaimer: Many people report feeling improvement in their condition and/or general well-being taking dietary, vitamin, mineral, and/or herbal supplements. The Editorial Board of, however, cannot endorse such products since most lack peer-reviewed scientific validation of their claims. In most cases an appropriate diet and a "multiple vitamin" will provide the necessary dietary supplements for most individuals. Prior to taking additional dietary, vitamin, mineral, and/or herbal supplements it is recommended that patients consult with their personal physician to discuss their specific supplement requirements.

Updated on: 01/22/19
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Thomas G. Lowe, MD
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