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Toxicity of Vitamin B12

Things You Need to Remember About the Toxicity of Vitamin B12

Vitamin B12 is good for our health in many ways. Though it is considered to be safe even when taken in doses higher than the recommended daily allowance, an overdose can sometimes cause certain side effects. It must therefore be taken under medical supervision. Read on to know more...
Bidisha Mukherjee
Last Updated: Apr 9, 2018
Quick Fact
According to the Institute of Medicine, which is a nonprofit organization in the United States, "No adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals."

Vitamin B12, which is also called cobalamin, is one of the eight vitamins that are a part of the vitamin B-complex family. This water-soluble vitamin performs various functions associated with the nervous system, cell metabolism, production of healthy red blood cells, and DNA synthesis. It is essential for the healthy functioning of the body. Adverse effects or the symptoms of toxicity have not been observed even after the administration of doses above the recommended intake. The low potential for adverse reactions is mainly due to the fact that it is soluble in water. Though the tolerable upper intake limit has not been set by the Food and Nutrition Board, it is best to refrain from taking B12 supplements in doses higher than the recommended dosage.
Recommended Dietary Allowance
The Recommended Dietary Allowance (RDA) of vitamin B12 for infants below the age of 6 months is 0.4 mcg. Infants in the age group of 6 to 12 months can be given 0.5 mcg. The RDA is between 0.7 mcg to 2 mcg for children in the age group of 1 to 10 years. For those above the age of 11, the RDA is 2.4 mcg. The RDA for pregnant women and breastfeeding mothers is 2.6 mcg and 2.8 mcg respectively. There isn't enough evidence on the effect of an overdose in pregnant women and breastfeeding mothers. Thus, they must adhere to the guidelines on dosage as per the advice of a medical expert.
Who Should Avoid Vitamin B12
Some people are allergic to cobalt or cobalamin. An allergic reaction can occur if they consume vitamin B12 supplements. Such a reaction may be characterized by symptoms such as itching, wheezing, tightness in chest, breathing problems, facial swelling and hives. Therefore, these people should strictly avoid this vitamin supplement. Those who have been diagnosed with Leber's disease (Leber hereditary optic neuropathy) must also avoid taking these supplements. Leber's disease is a hereditary eye condition that is associated with progressive loss of vision due to the degeneration of the optic nerve. It is believed that use of cobalamin supplements can aggravate the condition.
Associated Side Effects
» People who suffer from dermatological issues must be cautious while taking the supplements. Rosacea fulminans is a skin condition that is associated with the use of cobalamin supplements in such people. The symptoms can persist for quite a few months even after stopping the supplement. Medical treatment is required under such circumstances.
» Some other side effects that are observed after ingestion of this dietary supplement in people suffering from gastrointestinal problems are diarrhea, nausea and difficulty in swallowing.
» The stomach has the capacity to produce a proteinaceous substance known as Intrinsic Factor. This substance is essential for the absorption of vitamin B12. As we age, production of this protein decreases, which leads to deficiency of vitamin B12 in the elderly. Pernicious anemia and megaloblastic anemia are conditions caused by deficiency of vitamin B12. While supplementation of cobalamin is recommended for people suffering from such conditions, treatment of the deficiency through supplementation can put a person at a risk of developing certain conditions. For instance, supplementation for treatment of megaloblastic anemia can put a person at a risk of developing hypokalemia (low potassium levels). The symptoms of polycythemia vera (elevated RBC count in blood) can also become evident due to supplementation.
A heavy dosage of supplemental form of vitamin B12 is mostly considered harmless as the part of unabsorbed vitamin readily dissolves in water and can be flushed out of the body. Vitamin B12 toxicity is rare, but people suffering from vitamin B12 deficiency must take supplemental form of the vitamin in moderate amounts only. It is equally important that the supplements are taken only after consultation with the doctor.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.