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Associate Professor; Residency Director, Department of Family Medicine, University of California, Irvine
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Associate Professor; Residency Director, Department of Family Medicine, University of California, Irvine
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CME Released: 5/27/2005; Reviewed and Renewed: 5/26/2006
Valid for credit through: 5/26/2007, 11:59 PM EST
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May 27, 2005 -- In adults older than age 70 years, a dose more than 200 times the recommended dietary allowance (RDA) of B 12 is necessary to normalize mild deficiency, according to the results of a randomized study published in the May 23 issue of the Archives of Internal Medicine.
"Supplementation with high doses of oral cobalamin is as effective as cobalamin administered by intramuscular injection to correct plasma markers of vitamin B 12 deficiency, but the effects of lower oral doses of cobalamin on such markers are uncertain," write Simone J.P.M. Eussen, MSc, from Wageningen University in the Netherlands, and colleagues.
In this parallel-group, double-blind, dose-finding trial, the investigators assessed the effects of daily oral doses of 2.5, 100, 250, 500, and 1,000 µg of cyanocobalamin administered for 16 weeks on biochemical markers of vitamin B 12 deficiency in 120 older people. Study subjects had mild vitamin B 12 deficiency, defined as a serum vitamin B 12 level of 100 to 300 pmol/L (135 - 406 pg/mL) and a methylmalonic acid level of at least 0.26 µmol/L. The primary outcome was the dose of oral cyanocobalamin that produced 80% to 90% of the estimated maximal reduction in the plasma methylmalonic acid concentration.
Supplementation with cyanocobalamin at daily oral doses of 2.5, 100, 250, 500, and 1,000 µg was associated with mean reductions in plasma methylmalonic acid concentrations of 16%, 16%, 23%, 33%, and 33%, respectively. To achieve 80% to 90% of the estimated maximum reduction in the plasma methylmalonic acid concentration, daily doses of 647 to 1,032 µg of cyanocobalamin were required.
Study limitations include the variable absorption of vitamin B 12 in older people, current assay techniques that may misclassify a significant proportion of individuals with vitamin B 12 deficiency, lack of consensus about the cutoff points for vitamin B 12 deficiency or metabolites to define vitamin B 12 deficiency, and the extent to which differences in individual responses were due to active vs passive absorption of vitamin B 12.
"The lowest dose of oral cyanocobalamin required to normalize mild vitamin B 12 deficiency is more than 200 times greater than the recommended dietary allowance, which is approximately 3 µg daily," the authors write. "Clinical trials are currently assessing the effects of high doses of oral cobalamin on markers of cognitive function and depression. If such trials can demonstrate that the reported associations of vitamin B 12 deficiency with cognitive impairment or depression are causal and reversible by treatment, the relevance of correction of vitamin B 12 deficiency in older people could be substantial."
ZonMw in the Hague, Kellogg's Benelux, the Foundation to Promote Research Into Functional Vitamin B 12 Deficiency, and the European Union BIOMED Demonstration Project supported this study.
The authors report no financial disclosures.
Arch Intern Med. 2005;165:1167-1172
