Vitamin B-12 is one of the eight B vitamins that aids in converting food you consume into energy. Your body does not normally store B vitamins because they are all water-soluble. However, vitamin B-12 is the exception. Your body can store vitamin B-12 for years making deficiency a low risk in the general population. Although you can store this vitamin, it is not associated with overdose or toxicity when taken in excess.
Absorption and Low Toxicity
Vitamin B-12 binds to the proteins in food and when you consume B-12--containing foods it combines with hydrochloric acid in your stomach. The vitamin is then released from the protein in the food and next combines with intrinsic factor, a glycoprotein produced by the cells of your stomach lining. The intrinsic factor is necessary for your intestines to properly absorb the vitamin, which is then released into your bloodstream to aid in the formation of red blood cells. Your body uses the majority of vitamin B-12 and stores small amounts in the liver until it is needed. Excess consumption of vitamin B-12 is not associated with adverse effects and no tolerable upper limit is established because of the low toxicity risk.
Deficiency Symptoms
Vitamin B-12 is essential to your daily diet. No symptoms are associated with vitamin B-12 overdose but deficiency of this vitamin can occur. Individuals at risk for vitamin B-12 deficiency include the elderly, vegetarians and individuals with malabsorption problems. Atrophic gastritis is a condition common in the aging that reduces your ability to absorb vitamin B-12 because of decreased hydrochloric acid production in the stomach. The condition pernicious anemia also decreases your ability to absorb the vitamin in your gastrointestinal tract. Vegetarians are at high risk of deficiency because natural food sources of B-12 are animal-based. Deficiency symptoms include weakness, fatigue, tingling in the extremities, confusion and irritability or depression. Advanced deficiency symptoms can result in delirium, paranoia and impaired mental functioning. Treatment involves high dose oral or injection supplements prescribed by your physician.
Recommended Dietary Allowance
The recommended dietary allowance for daily intake of vitamin B-12 is relatively low at 2.4 mcg in adult men and women. Natural sources of vitamin B-12 for adults younger than 50 years of age are suggested instead of supplemental forms. A well-balanced diet that includes lean meat provides adequate vitamin B-12. Adults older than the age of 50 are suggested to take vitamin B-12 in supplemental form because of possible malabsorption problems, notes the Linus Pauling Institute. Supplements of 25 to 100 mcg per day is commonly used in the elderly with physician recommendation. No symptoms of overdose are associated with this type of high dose use of vitamin B-12. Medication interactions can occur with vitamin B-12 supplements including those for treating diabetes or peptic ulcer disease. Consult your physician for medication interaction information.
Food Sources
Shell fish like clams, mussels and crab are high in vitamin B-12 with 8 to 84 mcg per 3 oz. serving. Poultry and beef yields .3 to 2.1 mcg per 3-oz. serving and dairy foods like milk and yogurt are good sources at .9 to 1.4 mcg per 1-cup serving. Breakfast cereals and whole grain breads are often fortified with vitamin B-12 but you have to read product labeling to determine the percentage. No symptoms of overdose are associated with eating plenty of foods with vitamin B-12.
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