Does high folic acid intake affect unrecognized cobalamin deficiency, and how will we know it if we see it?

Department of Medicine, New York Methodist Hospital, Brooklyn, NY, and the Department of Medicine, Weill Medical College of Cornell University, New York, NY.
American Journal of Clinical Nutrition (Impact Factor: 6.77). 11/2009; 90(6):1449-50. DOI: 10.3945/ajcn.2009.28835
Source: PubMed
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    ABSTRACT: The success of folic acid fortification has generated consideration of similar fortification with cobalamin for its own sake but more so to mitigate possible neurologic risks from increased folate intake by cobalamin-deficient persons. However, the folate model itself, the success of which was predicted by successful clinical trials and the known favorable facts of high folic acid bioavailability and the infrequency of folate malabsorption, may not apply to cobalamin fortification. Cobalamin bioavailability is more restricted than folic acid and is unfortunately poorest in persons deficient in cobalamin. Moreover, clinical trials to demonstrate actual health benefits of relevant oral doses have not yet been done in persons with mild subclinical deficiency, who are the only practical targets of cobalamin fortification because >94% of persons with clinically overt cobalamin deficiency have severe malabsorption and therefore cannot respond to normal fortification doses. However, it is only in the severely malabsorptive disorders, such as pernicious anemia, not subclinical deficiency, that neurologic deterioration following folic acid therapy has been described to date. It is still unknown whether mild deficiency states, which usually arise from normal absorption or only food-bound cobalamin malabsorption, have real health consequences or how often they progress to overt clinical cobalamin deficiency. Reports of cognitive or other risks in the common subclinical deficiency state, although worrisome, have been inconsistent. Moreover, their observational nature proved neither causative connections nor documented health benefits. Extensive work, especially randomized clinical trials, must be done before mandatory dietary intervention on a national scale can be justified.
    Journal of Inherited Metabolic Disease 02/2011; 34(1):67-73. DOI:10.1007/s10545-010-9150-2 · 3.37 Impact Factor
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    ABSTRACT: In elderly individuals with low serum vitamin B-12, those who have high serum folate have been reported to have greater abnormalities in the following biomarkers for vitamin B-12 deficiency: low hemoglobin and elevated total homocysteine (tHcy) and methylmalonic acid (MMA). This suggests that folate exacerbates vitamin B-12-related metabolic abnormalities. We determined whether high serum folate in individuals with low serum vitamin B-12 increases the deleterious effects of low vitamin B-12 on biomarkers of vitamin B-12 cellular function. In this cross-sectional study, 2507 university students provided data on medical history and exposure to folic acid and vitamin B-12 supplements. Blood was collected to measure serum and red blood cell folate (RCF), hemoglobin, plasma tHcy, and MMA, holotranscobalamin, and ferritin in serum. In subjects with low vitamin B-12 concentrations (<148 pmol/L), those who had high folate concentrations (>30 nmol/L; group 1) did not show greater abnormalities in vitamin B-12 cellular function in any area than did those with lower folate concentrations (≤30 nmol/L; group 2). Group 1 had significantly higher holotranscobalamin and RCF, significantly lower tHcy, and nonsignificantly lower (P = 0.057) MMA concentrations than did group 2. The groups did not differ significantly in hemoglobin or ferritin. Compared with group 2, group 1 had significantly higher mean intakes of folic acid and vitamin B-12 from supplements and fortified food. In this young adult population, high folate concentrations did not exacerbate the biochemical abnormalities related to vitamin B-12 deficiency. These results provide reassurance that folic acid in fortified foods and supplements does not interfere with vitamin B-12 metabolism at the cellular level in a healthy population.
    American Journal of Clinical Nutrition 06/2011; 94(2):495-500. DOI:10.3945/ajcn.111.014621 · 6.77 Impact Factor
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    ABSTRACT: Cobalamin deficiency is relatively common, but the great majority of cases in epidemiologic surveys have subclinical cobalamin deficiency (SCCD), not classical clinical deficiency. Because SCCD has no known clinical expression, its diagnosis depends solely on biochemical biomarkers, whose optimal application becomes crucial yet remains unsettled. This review critically examines the current diagnostic concepts, tools, and interpretations. Their exploration begins with understanding that SCCD differs from clinical deficiency not just in degree of deficiency but in fundamental pathophysiology, causes, likelihood and rate of progression, and known health risks (the causation of which by SCCD awaits proof by randomized clinical trials). Conclusions from SCCD data, therefore, often may not apply to clinical deficiency and vice versa. Although many investigators view cobalamin testing as unreliable, cobalamin, like all diagnostic biomarkers, performs satisfactorily in clinical deficiency but less well in SCCD. The lack of a diagnostic gold standard limits the ability to weigh the performance characteristics of metabolic biomarkers such as methylmalonic acid (MMA) and holotranscobalamin II, whose specificities remain incompletely defined outside their relations to each other. Variable cutoff selections affect diagnostic conclusions heavily and need to be much better rationalized. The maximization of reliability and specificity of diagnosis is far more important today than the identification of ever-earlier stages of SCCD. The limitations of all current biomarkers make the combination of ≥2 test result abnormalities, such as cobalamin and MMA, the most reliable approach to diagnosing deficiency in the research setting; reliance on one test alone courts frequent misdiagnosis. Much work remains to be done.
    American Journal of Clinical Nutrition 07/2011; 94(1):348S-358S. DOI:10.3945/ajcn.111.013441 · 6.77 Impact Factor
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