Table 4.
Concentrations of serum folate forms and serum and red blood cell total folate by selected physiologic and lifestyle variables for the US population ≥1 year, NHANES 2011–2a
| Serum | RBC | ||||||
|---|---|---|---|---|---|---|---|
| Variable categories | 5-MethylTHF | UMFA | Non-methyl folate | MeFox | Total folate without MeFox | Total folate with MeFox | Total folate |
| (nmol/L) | |||||||
| Fasting time, hours | |||||||
| <3 | 39.1 (37.5–40.7) | 1.52 (1.44–1.61) | 1.57 (1.31–1.88) | 1.93 (1.84–2.03) | 43.7 (42.2–45.3) | 46.2 (44.6–47.8) | 1040 (1000–1080) |
| 3–<8 | 37.8 (35.8–40.0) | 1.40 (1.29–1.52) | 1.66 (1.37–2.00) | 1.96 (1.83–2.10) | 42.2 (40.1–44.4) | 44.8 (42.5–47.1) | 1050 (988–1120) |
| ≥8 | 36.3 (34.7–37.9) | .978 (.923–1.04) | 1.57 (1.29–1.92) | 1.17 (1.10–1.25) | 39.6 (38.2–41.1) | 41.1 (39.6–42.7) | 1060 (1020–1090) |
| P value | <0.0001 | <0.0001 | 0.19 | <0.0001 | <0.0001 | <0.0001 | 0.25 |
| P value adjusted | 0.0108 | <0.0001 | 0.44 | <0.0001 | 0.0170 | 0.0006 | 0.43 |
| eGFRb, mL/(min×1.73 m2) | |||||||
| 0–<60 | 42.3 (39.1–45.8) | 1.74 (1.57–1.92) | 1.80 (1.46–2.22) | 2.89 (2.66–3.15) | 47.5 (43.8–51.4) | 51.3 (47.6–55.2) | 1330 (1240–1430) |
| 60–<90 | 36.5 (34.8–38.3) | 1.24 (1.15–1.33) | 1.57 (1.31–1.89) | 1.61 (1.54–1.68) | 40.4 (38.7–42.2) | 42.5 (40.7–44.3) | 1100 (1060–1140) |
| ≥90 | 34.6 (33.0–36.3) | 1.05 (.988–1.13) | 1.52 (1.24–1.88) | 1.37 (1.26–1.48) | 38.1 (36.6–39.7) | 39.9 (38.3–41.5) | 982 (939–1030) |
| P value | 0.0001 | <0.0001 | 0.0406 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| P value adjusted | 0.48 | 0.0006 | 0.26 | <0.0001 | 0.42 | 0.11 | 0.0019 |
| BMIc | |||||||
| Underweight | 49.3 (46.3–52.4) | 1.62 (1.43–1.83) | 1.76 (1.49–2.07) | 1.36 (1.22–1.52) | 54.7 (51.7–57.8) | 56.6 (53.5–59.7) | 1010 (982–1040) |
| Normal weight | 38.8 (36.9–40.8) | 1.21 (1.14–1.30) | 1.55 (1.28–1.88) | 1.47 (1.36–1.59) | 42.8 (41.0–44.8) | 44.7 (42.8–46.8) | 1010 (973–1050) |
| Overweight | 36.7 (35.4–38.2) | 1.21 (1.14–1.29) | 1.55 (1.28–1.87) | 1.52 (1.44–1.61) | 40.5 (39.2–41.9) | 42.4 (41.0–43.9) | 1060 (1020–1110) |
| Obese | 33.3 (31.6–35.0) | 1.09 (.998–1.18) | 1.61 (1.30–1.99) | 1.65 (1.56–1.76) | 36.9 (35.2–38.6) | 39.0 (37.3–40.8) | 1090 (1040–1150) |
| P value | <0.0001 | 0.0002 | 0.0048 | 0.0001 | <0.0001 | <0.0001 | 0.0068 |
| P value adjusted | 0.0004 | 0.0015 | 0.73 | 0.0046 | 0.0004 | 0.0006 | 0.0026 |
| BSAd, cm×kg | |||||||
| <1.5 | 50.2 (47.8–52.8) | 1.55 (1.39–1.72) | 1.78 (1.50–2.10) | 1.41 (1.31–1.52) | 55.5 (53.1–58.0) | 57.4 (54.9–60.0) | 1040 (1020–1060) |
| 1.5–1.8 | 38.5 (36.2–40.9) | 1.23 (1.15–1.32) | 1.56 (1.28–1.90) | 1.53 (1.43–1.64) | 42.6 (40.2–45.1) | 44.6 (42.2–47.2) | 1020 (975–1060) |
| 1.8–2 | 36.0 (33.9–38.1) | 1.15 (1.09–1.22) | 1.55 (1.27–1.89) | 1.53 (1.43–1.63) | 39.6 (37.5–41.8) | 41.6 (39.4–43.8) | 1050 (995–1110) |
| ≥2 | 33.0 (31.3–34.8) | 1.11 (1.02–1.20) | 1.56 (1.29–1.89) | 1.57 (1.48–1.67) | 36.6 (35.0–38.2) | 38.6 (36.9–40.2) | 1080 (1030–1140) |
| P value | <0.0001 | <0.0001 | 0.0019 | 0.0009 | <0.0001 | <0.0001 | 0.24 |
| P value adjusted | 0.0053 | 0.0131 | 0.63 | 0.0159 | 0.0036 | 0.0040 | 0.0309 |
| Serum cotininee, μg/L | |||||||
| ≤10 | 39.6 (37.8–41.4) | 1.25 (1.19–1.32) | 1.60 (1.33–1.93) | 1.54 (1.46–1.63) | 43.6 (42.0–45.3) | 45.6 (43.9–47.4) | 1080 (1040–1130) |
| >10 | 29.3 (27.6–31.2) | 1.04 (.917–1.17) | 1.52 (1.22–1.89) | 1.49 (1.38–1.61) | 32.9 (31.3–34.7) | 34.8 (33.1–36.7) | 928 (877–981) |
| P value | <0.0001 | 0.0025 | 0.26 | 0.24 | <0.0001 | <0.0001 | <0.0001 |
| P value adjusted | <0.0001 | 0.0052 | 0.68 | 0.22 | <0.0001 | <0.0001 | <0.0001 |
| Alcohol intakef | |||||||
| No drinks | 38.2 (36.6–40.0) | 1.33 (1.25–1.42) | 1.68 (1.36–2.06) | 1.81 (1.73–1.89) | 42.5 (40.6–44.4) | 44.8 (42.9–46.8) | 1090 (1030–1140) |
| <1 (not 0) | 35.7 (33.9–37.6) | 1.18 (1.09–1.27) | 1.54 (1.26–1.89) | 1.53 (1.44–1.61) | 39.5 (37.7–41.4) | 41.4 (39.6–43.4) | 1060 (1010–1100) |
| 1–<2 | 31.7 (28.0–35.9) | 1.06 (.949–1.18) | 1.60 (1.34–1.91) | 1.45 (1.30–1.61) | 35.3 (31.6–39.5) | 37.2 (33.3–41.4) | 1110 (981–1250) |
| ≥2 | 30.5 (27.6–33.6) | .855 (.732–.998) | 1.52 (1.19–1.93) | 1.35 (1.14–1.59) | 33.6 (30.7–36.7) | 35.3 (32.4–38.5) | 1010 (940–1080) |
| P value | 0.0021 | 0.0003 | 0.14 | <0.0001 | 0.0018 | 0.0010 | 0.28 |
| P value adjusted | 0.0162 | 0.0002 | 0.57 | 0.0017 | 0.0108 | 0.0074 | 0.39 |
| Supplement useg | |||||||
| Yes | 52.9 (51.0–54.9) | 2.10 (1.92–2.29) | 1.78 (1.49–2.13) | 1.79 (1.67–1.92) | 59.2 (56.9–61.5) | 61.5 (59.2–63.9) | 1360 (1290–1430) |
| No | 33.6 (32.1–35.2) | 1.02 (.964–1.09) | 1.53 (1.26–1.87) | 1.44 (1.37–1.52) | 37.0 (35.7–38.4) | 38.9 (37.5–40.4) | 973 (940–1010) |
| P value | <0.0001 | <0.0001 | 0.0043 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| P value adjusted | <0.0001 | <0.0001 | 0.0008 | 0.0028 | <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; eGFR, estimated glomerular filtration rate; BSA, body surface area.
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-formyl-tetrahydrofolate, 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.
Used to assess renal function; available for persons ≥12 years; impaired renal function was defined as eGFR <60 mL/(min×1.73 m2)
BMI definitions (kg/m2): <18.5 (underweight); 18.5–>25 (normal weight); 25–<30 (overweight); and ≥30 (obese)
Calculated as square root of [(height in cm × weight in kg)/3600] or square root of [(height in inches × weight in pounds)/3131]
Biomarker of tobacco smoke exposure; concentrations >10 μg/L are considered to represent smokers
Calculated for participants ≥18 years as average daily number of “standard” drinks [(quantity × frequency)/365.25]; 1 drink ≈ 15 g ethanol
Folic acid-containing dietary supplements used in the last 24 hours prior to visiting the Mobile Examination Center