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E
Methodological Problems Associated with Laboratory Values and Food Composition Data for B Vitamins

TABLE E-1 Methodological Problems with Laboratory Values for B Vitamins

 

Thiamin

Riboflavin

Niacin

B6

Are precise, accurate methods available?

Yes

Yes

Yes

Yes

What is known about the analytic sensitivity and specificity of the methods?

Good

Good

Good

Good

Is there good agreement in results from use of different methods?

Yes

Yes

Yes

Yes, for most

Is there good agreement in results if different laboratories use the same methods?

Yes

Yes

Yes

Fair

Over time, how have changes in methods affected estimates?

Generally lower because of more specific chromatographic separation (especially high-performance liquid chromatography)



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OCR for page 456
DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline E Methodological Problems Associated with Laboratory Values and Food Composition Data for B Vitamins TABLE E-1 Methodological Problems with Laboratory Values for B Vitamins   Thiamin Riboflavin Niacin B6 Are precise, accurate methods available? Yes Yes Yes Yes What is known about the analytic sensitivity and specificity of the methods? Good Good Good Good Is there good agreement in results from use of different methods? Yes Yes Yes Yes, for most Is there good agreement in results if different laboratories use the same methods? Yes Yes Yes Fair Over time, how have changes in methods affected estimates? Generally lower because of more specific chromatographic separation (especially high-performance liquid chromatography)

OCR for page 456
DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline Folate B12 Pantothenic Acid Biotin Choline Needs improvement Yes Needs improvement Being improved Yes Good, but incomplete assays for all forms Fair; some metabolite interference noted Needs improvement Variable Mass spectrometry specific to 5 pmol No, see Gunter et al., 1996a No, e.g., Euglena gracilis gives lower values than does Lactobacillis leichmannii Fair, limited No Yes No, see Gunter et al., 1996a No, nonisotopic and radioassays do not agree closely Fair Fair, limited Yes Trends vary depending on method. Radioassays were unreliable before 1978. Recent introduction of nonisotopic assays has led to higher results. Little change in methods Generally lower now No change

OCR for page 456
DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline   Thiamin Riboflavin Niacin B6 How are problems with methods addressed in the report? Not necessary Earlier under-and over-estimations of flavins noted. Questions for research Not necessary a Gunter EW, Bowman BA, Caudill SP, Twite DB, Adams MJ, Sampson EJ. 1996. Results of an international round robin for serum and whole-blood folate. Clin Chem 42:1689–1694. TABLE E-2 Methodologic Problems with Obtaining Food Composition Data for B Vitamins   Thiamin Riboflavin Niacin B6 Are precise, accurate methods available?a Substantial, acceptable quality Substantial, acceptable quality Substantial, acceptable quality Substantial, acceptable quality Is there good agreement in results using different methods? Fair when allowance is made for specificity differences Over time, how have changes in methods affected estimates? None noted About the same or slightly lower None noted Slightly higher now a Ratings for the B vitamins (but not for choline) are taken from Life Sciences Research Office/Federation of American Societies for Experimental Biology. 1995. Third Report on Nutrition Monitoring in the United States. Washington, DC: U.S. Government Printing Office. b Quality of data was rated moot if it was considered unlikely that improved data for that food component would make a difference in the assessment of nutrition-related health status and the assignment of nutrition monitoring priority status (LSRO/FASEB, 1995).

OCR for page 456
DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline Folate B12 Pantothenic Acid Biotin Choline Detailed subsections, questions for research Need for internal reference is stated and values given when available; questions for research. Questions for research Short subsection Not necessary Folate B12 Pantothenic Acid Biotin Choline Conflicting, variable quality Conflicting, quality mootb Conflicting Lacking, being improved Substantial, acceptable quality No, see Gregory (1997), Martin et al. (1992), Pfeiffer et al. (1997), Tamura et al. (1997)c No, tissue methods poorly developed — Insufficient comparisons to assess Yes, but very limited experience New methods give somewhat higher results for some foods — — — Old estimates were too high, early assay not specific c Gregory JF 3rd. 1997. Bioavailability of folate. Eur J Clin Nutr 51: S54–S59; Martin DC, Francis J, Protetch J, Huff J. 1992. Time dependency of cognitive recovery with cobalamin replacement: Report of a pilot study. J Am Geriatr Soc 40:168–172; Pfeiffer CM, Rogers LM, Gregory JF 3rd. 1997. Determination of folate in cereal-grain food products using trienzyme extraction and combined affinity and reversed-phase liquid chromatography. J Agric Food Chem 45:407–413; Tamura T, Mizuno Y, Johnston KE, Jacob RA. 1997. Food folate assay with protease, α-amylase, and folate conjugase treatments. J Agric Food Chem 45:135–139.