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High doses of supplemental vitamin B12 needed to correct deficiency
The May 23 2005 issue of the American Medical Association journal Archives of Internal Medicine (http://archinte.ama-assn.org/) published the findings of Dutch researchers that much higher levels of vitamin B12 are needed to remedy a deficiency of the vitamin than are provided by the Netherlands’ recommended dietary allowance of approximately 3 micrograms per day. (In the US, the daily value for vitamin B12 is 6 mcg, however, the Institute of Medicine’s dietary reference intake is lower at 2.4 mcg per day.) A common means of correcting vitamin B12 deficiency is intramuscular injection of the vitamin, however, oral vitamin B12 has also been shown to be effective, although an optimal dose has not been determined.
Daily oral doses of 2.5, 100, 250, 500 and 1000 micrograms cyanocobalamin were administered for 16 weeks to 120 people aged 70 and older with vitamin B12 deficiency determined by low serum B12 and elevated plasma methylmalonic acid (MMA). Methylmalonic acid is a compound that is produced in the body when vitamin B12 is insufficient. Vitamin B12 is additionally needed to remethylate homocysteine to the amino acid methionine, therefore elevated total homocysteine can also be an indicator of B12 deficiency.
The participants’ blood samples were analyzed for cobalamin and MMA at 8 and 16 weeks. Plasma MMA was reduced in all participants at 8 weeks and remained stable through the study’s conclusion. Greater mean reductions in MMA were observed with increasing doses of vitamin B12, however, the highest dose of 1000 micrograms cyanocobalamin lowered MMA by the same percentage (33%) as 500 micrograms. Analysis of the data determined that the lowest dose resulting in 80 to 90 percent of the maximum reduction in MMA varied from 647 to 1032 micrograms per day.
The authors conclude that “the lowest dose of oral cyanocobalamin required to normalize biochemical markers of mild vitamin B12 deficiency in older people with a mild vitamin B12 deficiency is more than 200 times greater than the recommended dietary allowance for vitamin B12 of approximately 3 micrograms per day. Clinical trials are currently assessing the effects of high doses of oral cobalamin on markers of cognitive function and depression . . . However, the present trial demonstrates that much higher doses of cyanocobalamin are required to normalize vitamin B12 deficiency than were previously believed.”