TABLE 1.

Prefortification (1988–1994) and postfortification (1999–2010) blood folate concentrations by sociodemographic variable, dietary supplement use, and survey period in participants aged ≥4 y (NHANES 1988–2010)¹

	1988–1994		1999–2010		1988–1994		1999–2010
	n	Serum folate	n	Serum folate	n	RBC folate	n	RBC folate
		nmol/L		nmol/L		nmol/L		nmol/L
Total	23,359	16.7 ± 0.5	46,873	41.0 ± 0.3	22,846	747 ± 10	46,759	1120 ± 7
Age group
4–11 y	4627	29.6 ± 0.7	7379	56.1 ± 0.4	4498	851 ± 16	7380	1130 ± 7
12–19 y	2956	15.5 ± 0.6	10,614	39.5 ± 0.4	2888	642 ± 12	10,574	971 ± 8
20–39 y	6467	13.0 ± 0.4	10,044	35.1 ± 0.3	6335	674 ± 9	10,017	1020 ± 7
40–59 y	4258	15.5 ± 0.5	8966	38.9 ± 0.4	4180	763 ± 13	8945	1150 ± 10
60–79 y	3882	22.0 ± 0.6	7739	49.0 ± 0.5	3796	898 ± 15	7718	1350 ± 11
≥80 y	1169	26.2 ± 1.0	2131	57.8 ± 1.0	1149	965 ± 22	2125	1490 ± 19
P2		<0.001		<0.001		<0.001		<0.001
P-model 12,3		<0.001		<0.001		<0.001		<0.001
P-model 22,4		<0.001		<0.001		<0.001		<0.001
Gender
Male	11,130	15.8 ± 0.5	23,021	38.9 ± 0.3	10,877	734 ± 9	22,966	1090 ± 8
Female	12,229	17.7 ± 0.5	23,852	43.2 ± 0.3	11,969	759 ± 12	23,793	1150 ± 8
Age 15–44 y	5254	14.0 ± 0.5	9994	37.6 ± 0.3	5153	686 ± 12	9968	1060 ± 9
P5		<0.001		<0.001		0.001		<0.001
P-model 13,5		<0.001		<0.001		0.001		<0.001
P-model 24,5		0.008		<0.001		0.982		<0.001
Race/ethnicity
MA	7017	15.0 ± 0.5	11,822	37.4 ± 0.4	6820	696 ± 15	11,801	1020 ± 10
NHW	8533	17.5 ± 0.6	19,241	43.1 ± 0.4	8344	786 ± 12	19,171	1190 ± 10
NHB	6813	13.1 ± 0.3	10,722	34.3 ± 0.3	6695	573 ± 6	10,703	900 ± 5
P6		<0.001		<0.001		<0.001		<0.001
P-model 13,6		<0.001		<0.001		<0.001		<0.001
P-model 24,6		<0.001		<0.001		<0.001		<0.001
PIR
<1.0	6154	15.6 ± 0.6	10,772	37.7 ± 0.4	6009	687 ± 14	10,753	1020 ± 10
1.0–1.9	5909	15.8 ± 0.5	11,690	39.6 ± 0.3	5785	703 ± 12	11,656	1080 ± 9
2.0–3.9	6462	16.8 ± 0.5	11,318	41.4 ± 0.4	6299	758 ± 11	11,290	1130 ± 9
≥4.0	2756	19.0 ± 0.8	9520	43.3 ± 0.5	2707	830 ± 13	9488	1190 ± 10
P7		<0.001		<0.001		<0.001		<0.001
P-model 13,7		<0.001		<0.001		<0.001		<0.001
P-model 24,7		0.004		<0.001		0.001		<0.001
Supplement use8
Yes	7949	24.3 ± 0.7	15,294	49.9 ± 0.4	7776	923 ± 14	15,211	1320 ± 10
No	15,376	13.1 ± 0.3	23,356	35.4 ± 0.3	15,038	649 ± 7	23,287	994 ± 7
P9		<0.001		<0.001		<0.001		<0.001
P-model 13,9		NA		NA		NA		NA
P-model 24,9		<0.001		<0.001		<0.001		<0.001
Survey period
1999–2000		NA	7411	45.8 ± 1.0		NA	7393	1180 ± 24
2001–2002		NA	8242	42.7 ± 0.6		NA	8220	1160 ± 17
2003–2004		NA	7692	40.3 ± 0.7		NA	7618	1080 ± 16
2005–2006		NA	7639	41.1 ± 0.7		NA	7578	1140 ± 11
2007–2008		NA	7705	39.2 ± 0.9		NA	7728	1120 ± 23
2009–2010		NA	8184	37.9 ± 0.5		NA	8222	1040 ± 14
P10		NA		<0.001		NA		<0.001
P-model 13,10		NA		<0.001		NA		<0.001
P-model 24,10		NA		<0.001		NA		<0.001

¹Values are geometric means ± SE. Serum and RBC folate concentrations were measured from 1988–2006 by the Bio-Rad radioassay and assay-adjusted to be comparable to the microbiologic assay that was used from 2007–2010 (13, 16, 17). MA, Mexican American; NHB, non-Hispanic black; NHW, non-Hispanic white; NA, not applicable; PIR, poverty-to-income ratio.

²Test comparing group means across age categories.

³-value for multiple linear regression model 1 including age, gender, race/ethnicity, and PIR for prefortification data and age, gender, race/ethnicity, PIR, and survey period for postfortification data (1999–2010).

⁴ value for multiple linear regression model 2 including age, gender, race/ethnicity, PIR, and supplement use for prefortification data and age, gender, race/ethnicity, PIR, supplement use, and survey period for postfortification data (1999–2008).

⁵Test comparing males and females.

⁶Test comparing group means across race/ethnicity categories.

⁷Test of linear trend across PIR categories.

⁸Geometric means by dietary supplement use were limited to data from 1999–2008 for the postfortification period.

⁹Test comparing group means across supplement use categories.

¹⁰Test of linear trend across survey periods.