Vitamin B12 : Dosing

by MedlinePlus

(Page 2 of 3)

Adults (18 years and older):

Recommended daily allowances (RDAs):2.4mg/day for adults and adolescents aged 14 years and older, 2.6mcg/day for adult and adolescent pregnant females, 2.8mcg/day for adult and adolescent lactating females. Because 10-30% of older people do not absorb food-bound vitamin B12 efficiently, those over 50 years of age should meet the RDA by eating foods fortified with B12 or by taking a vitamin B12 supplement. Supplementation of 25-100mcg per day has been used to maintain vitamin B12 levels in older people.

Oral: The typical general supplemental dose of vitamin B12 is 1-25mcg per day. Formalabsorptionof vitamin B12 from food or pernicious anemia, cyanocobalamin doses of 300 to 2000mcg daily have been used. Forhyperhomocysteinemia, vitamin B12 in a dose of 500mcg in combination with 0.5 to 5mg folic acid and 16.5mg pyridoxine has been used. Todecrease the rate of restenosisafter coronary angioplasty, a combination of vitamin B12 400mcg plus pyridoxine (vitamin B6) 10mg and folic acid 1mg taken daily has been used, however unproven. Forreducingincreased homocysteineconcentrations associated with nitrous oxide general anesthesia, a supplement containing vitamin B12 500mcg with pyridoxine (vitamin B6) 25mg and folic acid 2.5mg taken daily for one week before surgery has been used. Forsickle cell disease,one study suggests that a practical daily combination may be 1mg folic acid, 6mcg vitamin B12, and 6mg vitamin B6. Some evidence suggests that 7.5mcg of vitamin B12 in combination with 5 grams of fish oil might be superior to fish oil alone when used daily toreduce total serum cholesterol and triglycerides.

Intramuscular (IM): For treatment ofvitamin B12 deficiency, the usual dose is 30mcg daily for 5-10 days. For maintenance therapy, 100-200mcg once monthly has been used. Both cyanocobalamin and hydroxocobalamin forms are used. For familial selectivevitamin B12 malabsorption, cyanocobalamin 1000mcg weekly for 3 weeks, followed by 250mcg monthly has been used. For relief oftremorassociated withshaky-leg syndrome, injections of 1000mcg of the cyanocobalamin form of vitamin B12 daily for two weeks, then weekly for two months, and once a month thereafter has been used. Fordecreasing homocysteine levelsand normalizing B12 levels in adult vegetarians, cyanocobalamin 1000mcg has been used. There is some evidence that intramuscular injections of 5mg of vitamin B12 given twice per week might improve the general well being and happiness of patients complaining of tiredness orfatigue, although unproven.

Children (younger than 18 years):

Recommended dietary allowances (RDAs):RDAs have not been established for all pediatric age groups therefore Adequate Intake (AI) levels have been used instead. The RDA and AI of vitamin B12 are: infants 0-6 months, 0.4mcg (AI); infants 7-12 months, 0.5mcg (AI); children 1-3 years, 0.9mcg; children 4-8 years, 1.2mcg; children 9-13 years, 1.8mcg.

Safety

Allergies

Vitamin B12 supplements should be avoided in people sensitive or allergic to cobalamin, cobalt or any other product ingredients.

Side Effects, Contraindications and Warnings

Cardiovascular: Caution should be used in patients undergoing angioplasty since an intravenous loading dose of folic acid, vitamin B6 and vitamin B12 followed by oral administration of folic acid 1.2mg plus vitamin B6 48mg and vitamin B12 60mcg taken daily after coronary stenting might actually increase restenosis rates. Due to the potential for harm this combination of vitamins should not be recommended for patients receiving coronary stents.

Dermatologic: Itching, rash, transitory exanthema, and urticaria have been reported. Vitamin B12 (20 micrograms/day) and pyridoxine (80mg/day) has been associated with cases of rosacea fulminans, characterized by intense erythema with nodules, papules, and pustules. Symptoms may persist for up to 4 months after the supplement is stopped, and may require treatment with systemic corticosteroids and topical therapy.

Gastrointestinal: Diarrhea has been reported.

Hematologic: Peripheral vascular thrombosis has been reported. Treatment of vitamin B12 deficiency can unmask polycythemia vera, which is characterized by an increase in blood volume and the number of red blood cells. The correction of megaloblastic anemia with vitamin B12 can result in fatal hypokalemia and gout in susceptible individuals, and it can obscure folate deficiency in megaloblastic anemia. Caution is warranted.

Leber's disease: Vitamin B12 is contraindicated in early Leber's disease, which is hereditary optic nerve atrophy. Vitamin B12 can cause severe and swift optic atrophy.

Pregnancy and Breastfeeding

Vitamin B12 is likely safe when used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA for vitamin B12 in pregnant women is 2.6mcg per day and 2.8mcg during lactation periods.

There is insufficient reliable information available about the safety of larger amounts of vitamin B12 during pregnancy.

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