Table 1.

Unweighted sample sizes for serum folate forms and serum and red blood cell total folate by selected demographic, physiologic, and lifestyle variable categories for the US population ≥1 year, NHANES 2011–2

Variable categories	5-MethylTHF	UMFA	Serum Non-methyl folate	MeFox	Total folate	RBC Total folate
All	7454	7462	7458	7469	7442	7867
Age, year
1–5	568	573	570	575	563	708
6–11	955	957	959	960	953	1044
12–19	1073	1074	1074	1074	1073	1127
20–39	1730	1730	1730	1730	1730	1762
40–59	1604	1604	1605	1606	1603	1655
≥60	1524	1524	1520	1524	1520	1571
Sex
Male	3739	3745	3746	3750	3735	3944
Female	3715	3717	3712	3719	3707	3923
Race-ethnicityb
Hispanic	1798	1803	1803	1806	1794	1919
Mexican American	989	993	995	996	987	1071
Other Hispanic	809	810	808	810	807	848
Non-Hispanic Asian	947	947	948	951	944	999
Non-Hispanic Black	2025	2027	2027	2027	2025	2185
Non-Hispanic White	2401	2402	2398	2402	2397	2471
Other	283	283	282	283	282	293
Fasting time, hours
<3	2476	2479	2475	2482	2469	2644
3–<8	1633	1637	1635	1637	1631	1744
≥8	3345	3346	3348	3350	3342	3479
eGFR stagec, mL/(min×1.73 m2)
0–<60	467	467	466	467	466	466
60–<90	2032	2032	2031	2033	2030	2039
≥90	3382	3383	3383	3384	3381	3428
BMId
Underweight	1203	1206	1204	1209	1197	1382
Normal weight	2297	2301	2301	2303	2295	2415
Overweight	1854	1854	1855	1855	1854	1882
Obese	1921	1921	1918	1921	1918	1970
BSAe, cm×kg
<1.5	1756	1762	1761	1766	1750	1971
1.5–1.8	1989	1990	1989	1991	1987	2069
1.8–2	1596	1596	1596	1597	1595	1640
≥2	1934	1934	1932	1934	1932	1969
Serum cotininef, μg/L
≤10	5938	5941	5937	5945	5929	6068
>10	1240	1240	1240	1241	1239	1259
Alcohol intakeg
No drinks	1474	1474	1472	1474	1472	1530
<1 (not 0)	2540	2540	2539	2541	2538	2602
1–<2	342	342	342	342	342	349
≥2	235	235	234	235	234	243
Supplement useh
Yes	1303	1305	1302	1306	1299	1370
No	5567	5573	5574	5579	5561	5882

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.

^aSerum folate forms and serum total folate (sum of all forms 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.

^bHispanic subgroup represents sum of Mexican American and other Hispanic ethnicity; other subgroup includes persons with multi-ethnic background.

^cUsed to assess renal function; available for persons ≥12 years; impaired renal function was defined as eGFR <60 mL/(min×1.73 m²)

^dBMI definitions (kg/m²): <18.5 (underweight); 18.5–>25 (normal weight); 25–<30 (overweight); and ≥30 (obese)

^eCalculated as square root of [(height in cm × weight in kg)/3600] or square root of [(height in inches × weight in pounds)/3131]

^fBiomarker of tobacco smoke exposure; concentrations >10 μg/L are considered to represent smokers

^gCalculated for participants ≥18 years as average daily number of “standard” drinks [(quantity × frequency)/365.25]; 1 drink ≈ 15 g ethanol

^hFolic acid-containing dietary supplements used during the last 24 hours prior to visiting the Mobile Examination Center