Table 3.

Trials using plasma concentration to assess the bioavailability of food folates or fortificants.

	Dose nmol 1	AUC or App Abs 2	Sampling duration (nr/4 h) 3	Females + males	Age 4	Ref.
Size of AUC (h∙nmol/L) from supplements and fortified foods
[13C6]-folic acid	634	19	8 h (8)	10 10	31 ± 1	[17]
Folic acid 5	1134	146	10 h (6)	0 + 13	26 ± 6	[64]
Folic acid	1134	40	10 h (6)	6 + 6	36-69	[45]
Folic acid	1193	37, 49 7	7 h (3)	8 + 8	20-50	[65]
Folic acid	907	62	10 h (4)	10 + 10	27 ± 3	[70]
[13C5]-folic acid in bread	450 (D)	28	12 h (7)	5 + 3	39-66	[46]
[13C5]-folic acid in breakfast meal	450 (D)	26	12 h (7)	5 + 3	39-66	[46]
(6S)-[13C6]-5-HCO-H4folate	500	42	8 h (8)	10 10	31 ± 1	[17]
(6S)-5-CH3-H4folate 5	1088	142	10 h (6)	0 + 13	26 ± 6	[64]
(6S)-5-CH3-H4folate 5	830 6	44, 88 6	10 h (7)	0 + 2	55, 77	[40]
(6S)-5-CH3-H4folate i.m. 5	830 6	111, 144 6	10 h (7)	0 + 2	55, 77	[40]
(6S)-[13C5]-5-CH3-H4folate in bread	450 (D)	66	12 h (7)	5 + 3	39-66	[46]
Size of AUC (h∙nmol/L) from native food folates
Broccoli 5	440 (M)	27, 41 6	10 h (7)	0 + 2	55, 77	[40]
Strawberries 5	450 (M)	32, 41 6	10 h (7)	0 + 2	55, 77	[40]
Spinach, monoglutamate 8	820 (T)	31	10 h (6)	6 + 6	36-69	[45]
Spinach, polyglutamate 9	990 (T)	27	10 h (6)	6 + 6	36-69	[45]
Spinach	544 (C)	41	10 h (4)	10 + 10	27 ± 3	[70]
	1088 (C)	71
Aleurone flour	1167 (M)	46, 38 7	7 h (3)	8 + 8	20-50	[65]
Wheat bran	213 (M)	8, 6 7	7 h (3)	8 + 8	20-50	[65]
Apparent absorption (%) from supplements, fortified foods and food folate
[13C6]-folic acid	634	24%	8 h (8)	14 10	33 ± 2	[18]
(6S)-[13C6]-5-HCO-H4folate	500	38%	8 h (8)	14 10	33 ± 2	[18]
Spinach [15N1-7]folate	588 (M)	44%	8 h (8)	14 10	33 ± 2	[18]
Folic acid in bread 5	491 6 (M)	74%	10 h (7)	1 + 8	51-79	[44]
(6S)-5-CH3-H4folate in fermented milk 5	450 6 (M)	86%	10 h (7)	1 + 8	51-79	[44]
Yeast folate 5	155 6 (M)	80%	10 h (7)	1 + 8	51-79	[44]

5-HCO-H₄folate: 5-formyltetrahydrofolate; 5-CH₃-H₄folate: 5-methyltetrahydrofolate; [13C5]-, [13C6]-: stable isotope-labeled (5 or 6 ¹³C); (6S)-: bioactive folate diastereoisomer; ¹ Folate content in food intervention doses quantified by (T: trienzyme, D: dienzyme or M: Monoenzyme extraction, or by C: calculation); ² App abs: apparent absorption, estimated by (kinetic modeling [18,42] or AUC: area under the curve (Mean or Median)); ³ Number of sampling occasions during 0-4 h post-dose in brackets; ⁴ Mean ± SD or range; ⁵ Presaturation with ~1 mg [38,42] or 5 mg [72] folic acid/day from day −9 to day −2 prior to each test day; ⁶ Conversion factors from µg to nmol: 0.441⁻¹ nmol/µg (folic acid) and 0.460⁻¹ nmol/µg (plasma folate and 5-methyltetrahydrofolate);⁷ Females and males reported separately; ⁸ Folate monoglutamates from enzymatic cleavage of endogenous spinach folates after cell disruption; ⁹ Native spinach folate polyglutamates; ¹⁰ No data on gender.