Comparison%20of%20Two%20DFE%20Instruments - J. Agric. Food...

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Comparison of Two Dietary Folate Intake Instruments and Their Validation by RBC Folate J ANEL E. O WENS , ² D IRK M. H OLSTEGE , AND A NDREW J. C LIFFORD * Department of Nutrition and Division of Agricultural and Natural Resources Analytical Laboratory, University of California, Davis, California 95616 An optimal folate nutritional status is important in minimizing developmental and degenerative disease. Therefore, constant monitoring of folate intake and of biomarkers of folate nutritional status is essential. The objective of this research was to compare two folate intake instruments and validate each one against RBC folate measured by a high-throughput liquid chromatography tandem mass spectrometry (HT LC-MS/MS) method described in the companion paper (Owens, J. E.; Holstege, D. M.; Clifford, A. J. J. Agric. Food Chem. 2007 , 55 , 3292 - 3297). A food frequency questionnaire (FFQ) and a folate-targeted semiquantitative Block dietary folate equivalents (DFE) screener were compared and individually validated against an HT LC-MS/MS method. RBC folate was 1178 ( 259 nmol/L (mean ( SD) in a population of 337 normal adult subjects. Folate intakes were 556 ( 265 μ g/day by the FFQ and 524 ( 276 μ g/day by the DFE screener. Folate intakes by the DFE screener were approximately 34 μ g less than by the FFQ (paired t test, p < 0.01), but the intake instruments were highly correlated for total folate intake ( r ) 0.608, < 0.01). Correlations between instruments and RBC folate were low ( < 0.35) but strong ( < 0.01). ROC curve analysis indicates that the measurement of RBC folate by the HT LC-MS/MS method is a better predictive tool than are intake instruments for the evaluation of marginal folate status. KEYWORDS: RBC folate; LC-MS/MS; analytical method; folate intake; FFQ; DFE screener INTRODUCTION Folates are important cofactors for one-carbon metabolism and for DNA base synthesis. Humans are unable to synthesize folate and depend on an adequate and constant intake. A daily recommended intake of 400 μ g of dietary folate equivalents (DFE) from a mix of natural food folates, folic acid food fortificants, and folic acid supplements is advised by the U.S. Food and Drug Administration ( 1 ). Since 1998, the U.S. FDA has required that most cereal and grain products in the United States be fortified with folic acid ( 1 ) to lower the incidence of neural tube defects (NTDs) ( 2 , 3 ). An adequate intake by women of child-bearing age is especially important to minimize NTD risk. The mandate to increase folate intake was successful as evidenced by the decrease in NTD affected births ( 4 ) and reflected by the near doubling of red blood cell (RBC) folate levels post-fortification ( 5 ). This response in RBC folate to fortification was higher than predicted and may be due to higher than expected intakes of folic acid fortified foods or a significant excess fortification of such products ( 5 , 6 ). At the same time, some uncertainty persists concerning the actual increase in folate
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Comparison%20of%20Two%20DFE%20Instruments - J. Agric. Food...

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