Table 2.
Concentrations of serum folate forms and serum and red blood cell total folate by demographic variable categories for the US population ≥1 year, NHANES 2011–2a
| Serum | RBC | ||||||
|---|---|---|---|---|---|---|---|
| Variable | 5-MethylTHF | UMFA | Non-methyl folate | MeFox | Total folate without MeFox | Total folate with MeFox | Total folate |
| (nmol/L) | |||||||
| All | 37.5 (36.0–39.1) | 1.21 (1.15–1.28) | 1.59 (1.32–1.92) | 1.53 (1.45–1.61) | 41.4 (40.1–42.9) | 43.4 (42.0–44.9) | 1050 (1010–1090) |
| Age, year | |||||||
| 1–5 | 53.6 (50.5–57.0) | 1.72 (1.46–2.02) | 1.92 (1.68–2.18) | 1.31 (1.12–1.52) | 59.5 (56.1–63.2) | 61.2 (57.7–65.0) | 1030 (985–1070) |
| 6–11 | 53.2 (50.3–56.4) | 1.55 (1.36–1.78) | 1.75 (1.44–2.13) | 1.39 (1.27–1.51) | 58.5 (55.4–61.8) | 60.4 (57.2–63.7) | 1060 (1020–1090) |
| 12–19 | 37.1 (34.8–39.5) | 1.10 (1.02–1.17) | 1.44 (1.18–1.75) | 1.33 (1.19–1.48) | 40.5 (38.4–42.7) | 42.2 (39.9–44.5) | 933 (899–969) |
| 20–39 | 32.0 (30.6–33.3) | 1.04 (.968–1.12) | 1.55 (1.22–1.96) | 1.41 (1.32–1.51) | 35.5 (34.2–36.8) | 37.3 (36.0–38.6) | 961 (922–1000) |
| 40–59 | 34.3 (32.3–36.4) | 1.14 (1.04–1.24) | 1.49 (1.25–1.78) | 1.51 (1.43–1.60) | 38.1 (36.0–40.3) | 40.0 (37.8–42.3) | 1060 (1000–1110) |
| ≥60 | 44.4 (42.1–46.8) | 1.49 (1.36–1.64) | 1.77 (1.49–2.11) | 1.98 (1.86–2.11) | 49.0 (46.7–51.5) | 51.7 (49.3–54.2) | 1260 (1200–1330) |
| P value | <0.0001 | <0.0001 | <0.0001 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| P value adjusted | <0.0001 | <0.0001 | 0.0002 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| Sex | |||||||
| Male | 35.8 (34.0–37.6) | 1.17 (1.09–1.25) | 1.57 (1.30–1.90) | 1.50 (1.40 1.60) | 39.6 (38.0–41.2) | 41.5 (39.8–43.2) | 1030 (982–1070) |
| Female | 39.2 (37.6–40.9) | 1.26 (1.18–1.34) | 1.60 (1.33–1.94) | 1.55 (1.48–1.64) | 43.3 (41.7–45.1) | 45.4 (43.7–47.2) | 1070 (1040–1110) |
| P value | 0.0002 | 0.0438 | 0.15 | 0.18 | 0.0004 | 0.0005 | 0.0040 |
| P value adjusted | 0.0001 | 0.0349 | 0.25 | 0.23 | 0.0002 | 0.0002 | 0.0039 |
| Race-ethnicityb | |||||||
| Hispanic | 36.1 (34.3–38.0) | 1.01 (.924–1.12) | 1.73 (1.26–2.38) | 1.26 (1.20–1.33) | 40.0 (38.1–42.0) | 41.7 (39.8–43.6) | 961 (937–984) |
| MA | 37.4 (34.8–40.2) | .984 (.872 1.11) | 1.78 (1.28–2.47) | 1.21 (1.13–1.29) | 41.2 (38.9–43.5) | 42.8 (40.5–45.1) | 973 (940–1010) |
| NH Asian | 37.2 (35.4–39.1) | .945 (.864–1.03) | 1.60 (1.28–2.00) | 1.59 (1.45–1.74) | 40.9 (39.1–42.8) | 43.1 (41.2–45.1) | 952 (911–994) |
| NH Black | 29.8 (28.2–31.4) | 1.19 (1.12–1.26) | 1.83 (1.35–2.46) | 1.21 (1.16–1.26) | 34.0 (32.2–35.8) | 35.6 (33.8–37.4) | 860 (830–892) |
| NH White | 39.4 (38.0–40.9) | 1.30 (1.23–1.37) | 1.52 (1.29–1.79) | 1.66 (1.59–1.74) | 43.3 (41.9–44.9) | 45.5 (44.0–47.0) | 1130 (1080–1170) |
| P value | <0.0001 | <0.0001 | 0.35 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| P value adjusted | <0.0001 | <0.0001 | 0.21 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
NHANES, National Health and Nutrition Examination Survey; 5-methylTHF, 5-methyltetrahydrofolate; UMFA, unmetabolized folic acid; MeFox, pyrazino-s-triazine derivative of 4α-hydroxy-5-methylTHF; RBC, red blood cell; MA, Mexican American; NH, non-Hispanic.
Values are geometric means (95% CI); serum folate forms and serum total folate (sum of folate forms excluding or including MeFox) were measured by HPLC-MS/MS; RBC total folate was measured by microbiologic assay; non-methyl folate represents sum of three minor forms: tetrahydrofolate, 5-formyltetrahydrofolate, and 5,10-methenyltetrahydrofolate; for sample sizes, see Table 1; P value is the unadjusted Wald F p-value, while P value adjusted is the Satterthwaite F P value adjusted for age, sex, and race-ethnicity.
Hispanic subgroup represents the sum of Mexican American and other Hispanic ethnicity; P values for race-ethnicity show comparison of Hispanic, NH White, NH Black, NH Asian, and other (not shown).