Vitamin B-12, an essential nutrient found in many animal-based foods and added to fortified foods and dietary supplements, plays an essential role in red blood cell production, DNA synthesis, neurological function and fat and protein metabolism. The body absorbs a limited amount of vitamin B-12 from foods and supplements, and the vitamin has a low potential for toxicity, according to the National Institutes of Health Office of Dietary Supplements. Consult your doctor to determine whether or not you should take vitamin B-12 supplements.
B-12 Absorption
The body absorbs only a small percentage of vitamin B-12 from dietary supplements because of the limited capacity of intrinsic factor, a glycoprotein in the stomach needed to absorb the vitamin. For example, healthy adults absorb only about 10 micrograms of a 500 microgram oral B-12 supplement, according to the National Institutes of Health Office of Dietary Supplements. The body excretes excess vitamin B-12 and other water-soluble vitamins in urine.
Tolerable Upper Intake
Because no existing evidence suggests that high amounts of vitamin B-12 have harmful effects, the Institute of Medicine has not established a tolerable upper intake level for this nutrient. Tolerable upper intake L=levels indicate the maximum daily intake of a nutrient likely to cause adverse effects.
Common Doses
Scientific research supports the use of 300 to 10,000 microgram doses of vitamin B-12 for the treatment of B-12 deficiency and pernicious anemia, according to MedlinePlus. Doctors may prescribe a 500 microgram dose of B-12 in combination with 0.5 to 5 mg of folic acid and 16.5 mg of pyridoxine to treat elevated homocysteine levels.
Deficiency Health Effects
While taking too much vitamin B-12 will not likely cause adverse effects, inadequate intake or adsorption of this vitamin can cause potentially serious health problems. B-12 deficiency anemia can cause weakness, fatigue, shortness of breath, constipation, diarrhea and unintended weight loss. Long-term vitamin B-12 deficiency can cause permanent damage to the peripheral nervous system and neurological functions, leading to confusion, depression, poor memory and, in severe cases, dementia.
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