Vitamin B-12 is a water-soluble vitamin found in meat, seafood and dairy foods. Vitamin B-12, also known as cobalamin, is essential for metabolism, normal red blood cell production and optimal central nervous system health. Doctors recommend supplemental vitamin B-12 to treat vitamin B deficiency. Toxicity from vitamin B-12 isn't likely, but taking it in supplement form can interact with certain drugs.
Vitamin B-12 Basics
Your body uses up most water-soluble vitamins quickly and excretes excess amounts through urination. Fat-soluble vitamins A, D, E and K can be stored in your fat and liver, so your body can use them as needed. Vitamin B-12 is different from other water-soluble vitamins in that your liver can store it, sometimes for years.
How Much You Need
The recommended dietary allowance, or RDA, for vitamin B-12 for people age 14 and older is 2.4 mcg a day for both males and females. Pregnant women need 2.6 mcg of vitamin B-12, and nursing mothers need 2.8 mcg. You can easily get enough vitamin B-12 from the foods in your diet if you eat meat. One slice of beef liver gives you 800 percent of your daily value for vitamin B-12, according to the Office of Dietary Supplements. Three oz. cooked clams and a serving of vitamin B-fortified breakfast cereal gives you 570 and 100 percent of your DV, respectively. Doctors may recommend oral vitamin B-12 or B-12 injections to treat dietary deficiencies, as well as deficiencies caused by certain medical conditions. Toxicity from vitamin B-12 isn't associated with excessive amounts of the vitamin, the Linus Pauling Institute says.
Vitamin B-12 and Toxicity
The Institute of Medicine of the National Academies has set no tolerable upper intake level, or UL, for vitamin B-12 because it's very unlikely to be toxic, regardless of whether you get it from dietary supplements or food. The Office of Dietary Supplements indicates that no adverse effects were associated with long-term intake of vitamin B-12 at 0.4 mg for slightly longer than three years and 1.0 mg for five years.
Vitamin B-12 Cautions
Vitamin B-12 may not mix well when combined with certain medications, including an antibiotic called chloramphenicol, proton pump inhibitors, histamine H2 receptor antagonists found in antacids, and metformin, a drug used to treat diabetes. Because symptoms of vitamin B-12 deficiency, such as lethargy and weakness, are resolved with supplemental vitamin B-12, some people believe that it can give them a boost of energy or increase athletic performance. However, absent a deficiency, there's no evidence to suggest that taking vitamin B-12 supplements in large doses will give you extra energy.
References
- University of Maryland Medical Center: Vitamin B12 - Overview
- MayoClinic.com; Vitamin B12; November 2010
- Office of Dietary Supplements; Vitamin B12 Fact Sheet; May 2010
- Linus Pauling Institute; Vitamin B12; Jane Higdon, Ph.D., et al.; March 2003
- Merck Manuals Online Medical Library; Vitamin B12; April 2007
- Better Health Channel: Vitamin and Mineral Supplements
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