Table 1. Characteristics of NHANES 1999–2002 participants by quartiles (Q) of red blood cell (RBC) folate and dietary folate equivalents (DFE)¹.

	RBC folate (ng/ml)				DFE (μg/d)
	Q1	Q2	Q3	Q4	Q1	Q2	Q3	Q4
	<237.8	237.8–<318.0	318.0–<422.0	≥422.0	<291.6	291.6–<467.0	467.0–<836.4	≥836.4
Characteristics2
n	341	361	350	350	345	353	351	338
Days of follow up	2193 ± 39	2096 ± 42	2179 ± 39	2187 ± 40	2162 ± 45	2193 ± 41	2201 ± 40	2091 ± 33
Age (years)	68.6 ± 0.4	69.2 ± 0.4	70.8 ± 0.5	71.2 ± 0.5	70.2 ± 0.5	69.7 ± 0.4	69.9 ± 0.5	69.6 ± 0.4
Gender, men (%)	59.2	55.1	50.6	44.9	44.3	54.1	57.6	55.6
Race/ethnicity (%)
Non-Hispanic white	41.4	55.2	69.1	75.4	49.3	56.9	63.5	71.1
Non-Hispanic black	29.6	15.4	8.9	5.3	21.1	16.2	12.0	10.1
Other race	29.0	29.4	22.1	19.3	29.6	26.9	24.5	18.9
Education level (%)
< High school	54.1	48.7	33.2	32.5	55.1	45.6	36.5	31.1
High school	18.9	20.5	27.2	23.4	19.1	23.8	22.5	25.7
> High school	26.9	30.8	39.5	44.2	25.8	30.6	41.0	43.2
Smoking (%)
Current	24.0	14.9	12.3	10.5	21.2	18.1	10.3	11.8
Former	34.6	40.6	36.4	36.8	33.9	35.4	40.7	41.7
Never	41.4	44.5	51.3	52.6	44.9	46.5	49.0	46.5
Physical activity (%)
Sedentary	29.0	31.1	25.8	29.5	35.5	30.3	27.9	24.9
Light	58.3	55.7	59.3	55.6	54.5	56.4	57.3	57.1
Moderate/high	12.7	13.2	14.9	14.9	9.7	13.1	15.0	18.1
Alcohol intake (gm/d)	6.5 ± 1.2	6.5 ± 1.1	4.0 ± 0.7	4.5 ± 0.9	4.2 ± 0.6	5.9 ± 1.1	6.1 ± 1.1	5.2 ± 0.9
BMI (kg/m2)	27.6 ± 0.3	28.4 ± 0.3	28.1 ± 0.3	28.0 ± 0.3	28.3 ± 0.3	28.1 ± 0.3	28.0 ± 0.3	27.7 ± 0.3
Total energy intake (kcal/d)	1730 ± 45	1797 ± 42	1807 ± 40	1760 ± 41	1186 ± 24	1725 ± 31	2044 ± 40	2111 ± 47
Folic acid supplement, users (%)	7.1	19.3	13.8	62.6	13.8	17.7	27.4	74.6

¹ Frequencies do not add up to 100% because of rounding and missing values.

² Mean ± SE for continuous variables, and percentages for categorical variables presented by quartiles of RBC folate and intake of DFE.