Vitamin B12, also known as cobalamin, is an important component of the diet. Vitamin B12 deficiency can result in detrimental health effects.
Individuals with certain health conditions, or on diets with strict protein restrictions can develop a vitamin B12 deficiency. Although symptoms are often manageable, severe complications including anemia can occur. Vitamin B12 supplements are generally safe and useful in treating patients who have a deficiency.
According to the U.S. Office of Dietary Suppplements, the recommended daily intake of vitamin B12 in most healthy adults is 2.4 mcg/day. Vitamin B12, also known as cobalamin, can be found in protein based food sources including fish, shellfish, meat and dairy products. Cyanocobalamin tablets for supplementation may contain 50 to 500 times the recommended daily allowance of vitamin B12. However, vitamin B12 absorption is limited by the availability of gastric intrinsic factor. Since vitamin B12 is water soluble, excess levels are easily eliminated by the kidneys.
Protein based foods contain large amounts of dietary vitamin B12. Since cobalamin is bound to proteins, gastric acid is required to cleave vitamin B12 from dietary proteins. The inner lining of the stomach produces a protein called intrinsic factor that combines with vitamin B12, allowing it to be absorbed into the body from the small intestine. Vitamin B12 is a vital component of many biological processes, including the synthesis of DNA and the creation of healthy nerve and red blood cells.
Individuals that are strict vegetarians may not have sufficient sources of vitamin B12 in their diets. Since gastric acid is required to cleave vitamin B12 from dietary proteins, the elderly and patients with medications or health conditions that cause a reduction in gastric acid may develop a vitamin B12 deficiency. Pernicious anemia is an autoimmune disease that can damage the inner linings of the stomach leading to impaired production of intrinsic factor. Since approximately 1 percent of vitamin B12 may still be absorbed in the absence of intrinsic factor, high-dose oral supplementation may still have some therapeutic benefits.
Symptoms of vitamin B12 deficiency may include fatigue, weakness, constipation and loss of appetite. In addition, vitamin B12 deficiency may also present as confusion, mood disorders and mouth soreness. In more severe cases, neurological symptoms such as tingling and numbing in the hands or megaloblastic anemia can develop. Treatment often involves the use of oral vitamin B12 supplements or prescription cyanocobalamin intramuscular injections.
Allergic reactions to vitamin B12 supplements, including rash and itching, can occur in patients allergic to cobalamin or cobalt. Vitamin B12 can also exacerbate certain blood cell disorders and is contraindicated in Leber’s disease, a rare eye disorder. According to the Office of Dietary Supplements, both the Norwegian Vitamin Trial (NORVIT) and the Heart Outcomes Prevention Evaluation-2 Study (HOPE 2) found that patients with vitamin B12 intake of 400 to 1000 mcg/day for up to five years reported no serious adverse effects. Patients should consult a phycisian if they have concerns regarding vitamin B12 deficiency.
Institute of Medicine: "Dietary Reference Intakes".
MayoClinic.com: "Vitamin B12" .
Office of Dietary Supplements: "Vitamin B12 Fact Sheet".
