FIGURE 1.

Mean (A) and percentage concentrations (B) of unmetabolized serum folic acid (UMFA) and serum 5-methyltetrahydrofolate (MTHF, 5-methylTHF) in US adults aged ≥60 y with detectable UMFA by 5-methylTHF quartile. Data are from the National Health and Nutrition Examination Survey (http://www.cdc.gov/nchs/nhanes/about_nhanes.htm). Reasons for exclusion were elevated concentrations of serum creatinine or alanine amino transferase, 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. ^*Quartile 4 was significantly different from other quartiles, P ≤ 0.006 (Bonferroni-adjusted for multiple comparisons). Numbers above each bar represent the black portion of that bar.