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Vitamin B12 is known as cobalamin. It is the largest vitamin molecule and also the only vitamin that contains the element cobalt. Methylcobalamin and adenosylcobalamin are the two forms of “active” vitamin B12 used by the body.
Your body cannot make vitamin B12. It is synthesized only by bacteria. While present in animal products, including meats, fish, shellfish, dairy products, and eggs, it is absent in plant- based foods.
Vitamin B12 deficiency is characterized by a specific type of anemia called megaloblastic anemia. It can cause fatigue, weakness, constipation, loss of appetite, and weight loss. Numbness and tingling in the hands and feet, depression, confusion, or poor memory can also occur.
People most at risk for B12 deficiency arevegans, as diets devoid of animal products will result in B12 deficiency. However, B12 issues can be caused by taking some types of stomach acid blockers. Also, some peopl have an autoimmune or inflammatory condition of the stomach wall that degrade the proteins that aid vitamin B12 absorption.
Symptoms of B12 deficiency can take decades to develop, and can usually only be diagnosed by a medical professional.
The Recommended Dietary Allowance for vitamin B12 is 2.4 micrograms per day (μg/day) for adolescents and adults. It is slightly higher for women who are pregnant (2.6 μg/day) or breastfeeding (2.8 μg/day).
Because of the increased risk of malabsorption by adults over 50 years of age, they should get most of their B12 from fortified food or supplements. The Linus Pauling Institute recommends adults older than 50 years take 100 to 400 μg/day of supplemental vitamin B12. Others may also have difficulty absorbing vitamin B12 from food, but determining this requires an evaluation of vitamin B12 status by a medical practitioner.
No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people.