B12, or cobalamin, is one of many essential B vitamins. It is important for metabolism, the process that converts food into energy, and for the formation of red blood cells. B12 also supports proper functioning of the nervous system. A B12 deficiency can result in serious medical conditions that may require vitamin therapy through supplements or B12 injections.
Sources and RDA
Dietary sources of B12 include eggs, meat, poultry, shellfish, milk and dairy products, according to Medline Plus. The recommended dietary allowance of B12 for infants up to 12 months is 0.4 to 0.5 micrograms per day. Children ages 1 to 13 need 0.9 to 1.8 mcg/day, depending on their age. Adolescents age 14 and older and adults need 2.4 mcg/day of B12.
Deficiency
According to the Office of Dietary Supplements, a B12 deficiency can result in anemia, fatigue, weakness, constipation, loss of appetite, weight loss, numbness and tingling in the extremities, difficulty balancing, depression, confusion, dementia, poor memory and soreness of the mouth or tongue.
Individuals at risk for a B12 deficiency include older adults, individuals with pre-existing anemia, vegetarians and those with intestinal disorders or who have had intestinal surgery. B12 deficiencies require vitamin therapy and can be treated with vitamin injections or oral supplements. The ODS says that vitamin B12 toxicity is rare and, according to the Institute of Medicine, "no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals."
Supplements
Oral B12 supplements are available as tablets and lozenges. B12 can be taken by itself or as part of a B vitamin complex that combines many B vitamins. The ODS says the body’s ability to absorb oral B12 supplements is limited and only about 10mcg of a 500mcg supplement is absorbed in the body. According to the Mayo Clinic 25 to 100mcg of oral B12 have been used to maintain normal levels of B12 in older individuals.
Injections
B12 injections are often preferred over oral B12 because they bypass barriers that may affect absorption of the vitamin, according to the ODS. Injections are most often prescribed to treat pernicious anemia, a blood disorder, and B12 deficiencies that result from an inability to absorb B12. Medline Plus says B12 injections for pernicious anemia are usually administered once a day for the first six to seven days of treatment. After the first week, injections are given every other day for two weeks and then every three to four days for the next two to three weeks. When the anemia resolves, injections may be given once a month for the rest of a patient’s life to prevent it from returning.
Side Effects
The Mayo Clinic says B12 supplements can cause itching, rash, hives and diarrhea. According to Medline Plus, common side effects of B12 injections include diarrhea and a feeling of swelling over the entire body. Serious but uncommon side effects of B12 injections include muscle weakness, cramps or pain, increased thirst or urination, confusion, difficulty breathing, coughing, increased heart rate, extreme fatigue, swelling of the extremities, headache, dizziness, hives, rash, itching and difficulty swallowing. According to the ODS, B12 can interact with the antibiotic chloramphenicol, medications used to treat acid reflux disease and ulcers and metformin, a diabetic medication used to lower blood sugar.
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