Excessive Vitamin B-12 In The Body

Many patients take over-the-counter vitamin B-12 supplements to prevent or treat vitamin B-12 deficiencies, while others take it by prescription. Dosages vary widely and even relatively large doses -- sometimes up to 1,000 mcg a day -- rarely cause side effects. High levels of vitamin B-12 generally occur as a result of a liver or blood disorder. If you have questions about the dosage of vitamin B-12 you should take, check with your health-care provider for more information.

Vitamin B-12

Vitamin B-12, also called cyanocobalamin, helps the body to produce red blood cells, RNA and DNA, and also plays important roles in the cardiovascular and immune systems. Vitamin B-12 occurs naturally in foods such as eggs, fish and meat, but does not occur in plants. Vitamin B-12 supplements come in oral, nasal and intramuscular injection forms used to prevent or treat vitamin B-12 deficiency. Some forms require a prescription, while others may be purchased over-the-counter.

Vitamin B-12 Levels

The normal level of vitamin B-12 in the blood, measured in picograms per milliliter, ranges between 200 to 900 pg/mL, according to MedLinePlus. Vitamin B-12 deficiency, a level below 200 pg/mL, may result from surgery on the stomach, reduced intrinsic factor -- a substance that helps the body absorb vitamin B-12 from food -- or eliminating animal foods from the diet. Rarely, patients may have high vitamin B-12 levels due to liver disease or blood disorders.

Vitamin B-12 Stores

The body can store about 2,000 mcg of vitamin B-12 in the liver, according to Linda Aills, R.D., lead researcher in a study published in the September 2008 issue of "Surgery for Obesity and Related Disease." An excess of vitamin B-12 does not happen frequently, as a healthy person normally excretes any excess in his urine. However, conditions such as hepatitis, cirrhosis of the liver and blood disorders such as polycythemia vera and chronic myelocytic leukemia may have high levels of vitamin B-12.

Side Effects of Vitamin B-12

Some patients receive large doses of vitamin B-12, up to 500 to 1,000 mcg intramuscularly every day for several weeks to treat vitamin B-12 deficiency, according to Drugs.com. Although side effects occur rarely, they may include muscle cramps, pain, weakness, leg pain, thirst, confusion, shortness of breath, urinary frequency, coughing, rapid heartbeat, fatigue, swollen extremities, dizziness, headache, hives, rash or difficulty breathing. Patients who experience serious side effects should seek medical attention immediately.