IHN Database

Effectiveness of vitamin B12 supplementation

DENVER, COLORADO. It is estimated that about 16% of older adults are vitamin B12 (cobalamin) deficient. This deficiency is mostly related to an inability to absorb cobalamin bound to food. Several experiments have shown that this problem does not affect people's ability to absorb free or synthetic cobalamin. A lack of vitamin B12 can lead to megaloblastic anemia and, if untreated, to irreversible neurological damage that may mimic Alzheimer's disease. There is ample evidence that injections of cobalamin can quickly correct a deficiency as can oral supplementation with 1-2 mg/day. It is not clear, however, whether smaller amounts, such as the 25 mcg or so found in multivitamins, are sufficient to correct a deficiency.

A team of researchers from the universities of Washington and Colorado has just released a study designed to determine just how much oral cobalamin supplementation is required to reverse a deficiency. The study involved 23 older patients who had been diagnosed as being vitamin B12 deficient (serum cobalamin level less than 221 pmol/L and serum methylmalonic acid [MMA] level greater than 271 nmol/l). All participants received 25 mcg/day of cobalamin during the first 6 weeks, 100 mcg/day during the next 6 weeks, and 1000 mcg/day during the final 6 weeks of the study. Two participants achieved normal MMA levels with the 25 mcg/day dose, an additional 5 with the 100 mcg/day dose, but it took 1000 mcg/day (1 mg/day) before an additional 12 regained normal MMA levels. Thus 19 out of 23 patients (83%) normalized their MMA level and eliminated their vitamin B12 deficiency at a daily intake of 1000 mcg/day. The 1000 mcg/day dose was also effective in lowering homocysteine level in 75% of the patients, but folic acid supplementation was required in 4 of the patients in order to bring homocysteine concentrations down to an acceptable level.

The researchers conclude that most cobalamin-deficient older people require more than 100 mcg/day of oral cobalamin to correct their deficiency.
Rajan, S, et al. Response of elevated methylmalonic acid to three dose levels of oral cobalamin in older adults. Journal of the American Geriatrics Society, Vol. 50, November 2002, pp. 1789-95

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