Folate Intake and Markers of Folate Status in Women of Reproductive Age, Pregnant and Lactating Women: A Meta-Analysis

Table 3

Effects of total folate supply (i.e., folic acid plus dietary folate)¹ on folate in plasma/serum and in red blood cells, as well as on plasma homocysteine levels in women, stratified by population group, duration of supplementation, and dose of folic acid supplementation.

Stratum for analysis	Folate in plasma/serum			Folate in red blood cells			Total plasma homocysteine
	No. of studies (n participants)	Regression coefficient [95% CI]	Heterogeneity 𝐼^2 (%)	No. of studies (n participants)	Regression coefficient [95% CI]	Heterogeneity 𝐼^2 (%)	No. of studies (n participants)	Regression coefficient [95% CI]	Heterogeneity 𝐼^2 (%)
All studies	9 (632)	0.56***; [0.40, 0.72]	92	10 (724)	0.30***; [0.22, 0.38]	82	9 (585)	−0.10**; [−0.17, −0.04]	72
Population group
Women in childbearing age	4 (343)	0.65***; [0.39, 0.92]	96	7 (486)	0.33***; [0.23, 0.44]	86	6 (470)	−0.12***; [−0.15, −0.08]	0
Pregnant women	3 (204)	0.52***; [0.30, 0.75]	69	1 (153)	0.26***; [0.15, 0.37]	n.a	1 (30)	−0.42***; [−0.58, −0.25]	n.a
Lactating women	2 (85)	0.36; [0.08, 0.79]	90	2 (85)	0.19***; [0.09, 0.28]	0	2 (85)	0.03; [−0.04, 0.11]	0
Duration of supplementation
4–12 weeks	4 (317)	0.51***; [0.22, 0.80]	96	6 (415)	0.27***; [0.17, 0.37]	83	6 (444)	−0.10***; [−0.14, −0.05]	31
13–20 weeks	1 (43)	0.58***; [0.38, 0.77]	n.a	1 (43)	0.26**; [0.08, 0.44]	n.a	1 (43)	0.03; [−0.06, 0.12]	n.a
≥21 weeks	4 (272)	0.60***; [0.38, 0.82]	84	3 (266)	0.39***; [0.23, 0.55]	76	2 (98)	−0.26; [−0.55, 0.04]	90
Dose
≤250 𝜇g FA/day	2 (120)	0.61*; [0.05, 1.17]	82	2 (146)	0.28; [−0.06, 0.62]	70	2 (146)	−0.13; [−0.28, 0.02]	68
251–500 𝜇gFA/day	7 (569)	0.59***; [0.41, 0.76]	93	9 (682)	0.32***; [0.23, 0.40]	82	8 (543)	−0.12***; [−0.18, −0.06]	69
>500 𝜇g FA/day	1 (42)	0.13; [−0.07, 0.33]	n.a	1 (42)	0.16**; [0.04, 0.27]	n.a	1 (42)	0.05; [−0.08, 0.18]	n.a

¹ The amounts of folic acid from supplements/fortified foods were transformed into amounts of folate by multiplying × 1.7 (IOM, 2000; [6]). When not provided in the RCT, the dietary folate intake used corresponded to the mean value of 247 𝜇g/day.
n.a: not applicable.
Test for overall effect (P): *<0.05, **<0.01, ***<0.001.