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. 2010 Jun 23;92(2):383–389. doi: 10.3945/ajcn.2010.29499

FIGURE 2.

FIGURE 2

The percentage of US adults (aged ≥60 y) without detectable concentrations of unmetabolized serum folic acid (UMFA−) and with detectable concentrations of UMFA (UMFA+) by quartiles of serum 5-methyltetrahydrofolate (5-Methyl THF) concentration (A), quartiles of total folic acid intake (B), red blood cell (RBC) folate concentration (C), and serum folate concentration (D). Data are from the National Health and Nutrition Examination Survey (http://www.cdc.gov/nchs/nhanes/about_nhanes.htm). Reasons for exclusion were elevated serum creatinine or alanine amino transferase concentration, self-reported anemia, use of folate-blocking cancer therapy, missing or incomplete dietary data, or self-reported folic acid supplement use in the fasting period before blood draw. UMFA and 5-methylTHF in serum were measured by using affinity/HPLC with electrochemical (coulometric) detection. Serum folate and RBC folate were assessed by radioassay. There was a significant P for trend across quartiles of 5-methylTHF (A), total folic acid intake (B), RBC folate (C), and serum folate (D). P ≤ 0.006 across quartiles for the UMFA+ group (Bonferroni-adjusted).