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B12 Deficiency, Higher Serum Folate Causes Adverse Effects

B12's enzymatic functions worsen as folate status increases in people who are B12-deficient

FRIDAY, Dec. 28 (HealthDay News) -- Among people with low serum vitamin B12 concentrations, high plasma folate is associated with higher concentrations of the two indicators of impaired B12 status: total homocysteine and methylmalonic acid, researchers report in the Dec. 11 issue of the Proceedings of the National Academy of Sciences.

Jacob Selhub, Ph.D., of Tufts University in Boston, and colleagues analyzed data on adults who participated in phase 2 of the National Health and Nutrition Examination Survey III (1991-1994) and the National Health and Nutrition Examination Survey (1999-2002).

The researchers found that concentrations of both metabolites decreased significantly as serum folate increased in subjects with high serum vitamin B12 levels above 148 pmol/L. In subjects with lower vitamin B12 serum levels, however, they found that concentrations of both metabolites increased as serum folate increased, starting at about 20 nmol/L.

"These observations provide a possible biochemical explanation for high folic acid intake's exacerbation of the clinical manifestations of vitamin B12 deficiency," the authors conclude.

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