TABLE 1.
Unmetabolized serum folic acid (UMFA) and its relation to selected demographic, dietary, and biomarker variables presented by participants without (UMFA−) and with (UMFA+) UMFA for adults aged ≥60 y in the United States (2001–2002)1
| Variables | All subjects (n = 1121) | UMFA− (n = 756) | UMFA+ (n = 365) |
| Demographic | |||
| Age (y) | 70 ± 0.5 | 71 ± 0.3 | 70 ± 0.5 |
| Male (%) | 42 ± 2 | 44 ± 2 | 38 ± 2 |
| Non-Hispanic white (%) | 82 ± 1 | 80 ± 1 | 86 ± 1 |
| Folic acid supplement users (%) | 47 ± 2 | 40 ± 2 | 61 ± 3* |
| Dietary | |||
| Dietary folic acid (μg) | 178 ± 8 | 164 ± 11 | 202 ± 10 |
| Dietary total folate (DFEs) | 517 ± 16 | 489 ± 21 | 564 ± 18 |
| Supplemental folic acid (μg) | 175 ± 10 | 140 ± 11 | 235 ± 21* |
| Total folic acid (μg)2 | 353 ± 14 | 303 + 17 | 437 ± 20* |
| Total energy-adjusted folic acid (μg) | 105 ± 5 | 99 ± 7 | 113 ± 6 |
| Biomarker3 | |||
| Serum UMFA (nmol/L) | 1.7 ± 0.2 | — | 4.4 ± 0.6 |
| Serum 5-methyltetrahydrafolate (nmol/L) | 49.3 ± 1.0 | 45.7 ± 1.3 | 55.2 ± 1.6* |
| Red blood cell folate (nmol/L) | 831 ± 16 | 810 ± 24 | 866 ± 17 |
| Serum folate (nmol/L) | 42 ± 0.9 | 37 ± 0.9 | 51 ± 2.6* |
| Serum vitamin B-12 (pmol/L) | 402 ± 14 | 384 ± 17 | 432 ± 12* |
| Serum methylmalonic acid (μmol/L) | 0.19 ± 0.1 | 0.20 ± 0.01 | 0.18 ± 0.01 |
| Serum homocysteine (μmol/L) | 10.4 ± 0.2 | 10.6 ± 0.1 | 10.2 ± 0.4 |
| Serum cotinine (ng/mL) | 33.1 ± 3.6 | 34.3 ± 4.2 | 31.0 ± 6.5 |
All values are means or percentages ± SEs. DFEs, dietary folate equivalents. For all variables other than those presented under Demographics, the results were controlled for sex, age, and race-ethnicity. 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. *Group differences were significant at P ≤ 0.006 (Bonferroni-adjusted for multiple comparisons).
Total folic acid represents the sum of dietary and supplemental consumption.
All values were controlled for session of blood collection and length of fast before blood draw. Significance level was obtained from variables in the log-transformed scale. UMFA and 5-methyltetrahydrafolate in serum were measured by using affinity/HPLC with electrochemical (coulometric) detection. Serum folate, red blood cell folate, and serum vitamin B-12 were assessed by radioassay, and plasma homocysteine was assessed by immunoassay. Plasma methylmalonic acid was measured by gas chromatography–mass spectrometry. Serum cotinine was analyzed by an HPLC/atmospheric-pressure ionization tandem mass spectrometry method.