Dietary and lifestyle predictors of folate insufficiency in non-supplemented German women

Figures & data

Figure 1. Folate intake is a determinant of folate status. The relationship is influenced by several effect modifiers. Therefore, a dose–response relationship between intake and status markers is not necessarily present in a population with a generally low intake and no additional sources of folate.

Table 1. Characteristics of the 198 participants and their folate markers.

	Median (25th–75th percentiles)
Age, years	25 (22–29)
BMI, kg/m^2	21.5 (20.1–23.0)
Creatinine, mg/dL	0.76 (0.71–0.84)
ALT, U/L	16 (13–20)
AST, U/L	18 (15–21)
Fasting glucose, mmol/L	82 (79–87)
Hemoglobin, g/dL	13.2 (12.5–13.8)
Haematocrit, %	39.3 (37.7–41.1)
Mean corpuscular volume, fL	87.2 (84.8–90.1)
Smokers, n (%)	33 (16.7)
Using contraceptive hormones, n (%)^a	120 (60.6)
Physically active, n (%)^b	153 (77.3)
Women having children, n (%)	34 (17.2)
Education level, n (%)
Less than university	55 (27.8)
University student	69 (34.8)
University degree or higher	74 (37.4)
Folate status markers
RBC-folate, nmol/L	589 (438–771)
RBC-folate < 405 nmol/L, n (%)	37 (18.7)
RBC-folate ≥ 952 nmol/L, n (%)	19 (9.6)
Serum folate, nmol/L	14.7 (11.3–20.5)
Serum folate < 7 nmol/L, n (%)	7 (3.5)
tHcy, µmol/L	7.3 (6.1–8.4)

^a Hormonal contraceptives were defined as oral contraceptives or using any other hormonal preparations (i.e. delivered via devices).

^b Physically active was defined as practicing sports regularly.

Concentrations of folate were measured by using IMMULITE 2000. ALT: alanine transaminase; AST: aspartate transaminase; BMI: body mass index; RBC: red blood cell.

Table 2. Nutrient intakes in 198 German women of childbearing age.

Nutrients or nutritional values	Median (25th–75th percentiles)
Energy, kcal	1856 (1587–2206)
Total protein intake, g	69 (57–83)
Protein, % of total energy	16 (14–17)
Total fat intake, g	77 (62–91)
Fat, % of total energy	37 (33–40)
Carbohydrates, g	209 (175–248)
Carbohydrates, % of total energy	47 (42–51)
Total fibre intake, g	21 (17–26)
Polyunsaturated fatty acids, g	12 (9–16)
Total cholesterol intake, mg	268 (192–358)
Total vitamin intake per 1000 Kcal
Vitamin B6, mg	0.81 (0.68–0.92 )
Vitamin B12, µg	1.66 (1.32–2.22)
Folate, µg	154 (123–187)^a
Vitamin B1, mg	0.62 (0.54–0.72)
Vitamin B2, mg	0.72 (0.65–0.83)
Biotin, µg	24.7 (21.3–30.1)
Niacin, µg	13.7 (12.4–15.9)
Pantothenic acid, mg	2.3 (2.0–2.8)
Vitamin E, mg	6.2 (4.9–7.9)
Vitamin C, mg	67.9 (48.2–89.7)
Iodine, µg	44.4 (36.1–53.1)
Vitamin A, µg	621 (496–932)

Intake values were mean of 2 × 3-d food protocols repeated twice within 8 weeks. The results of the food protocol were analysed using EBISPro software based on a country-specific nutrient content database (details are in materials and methods). All women were not receiving any supplementation.

^a Median (25th–75th percentiles) of folate not adjusted for energy intake is 278 (229–361) µg/d.

Table 3. Concentrations of folate biomarkers, dietary intakes and characteristics of 198 German women according to quartiles of RBC-folate.

	Q1 lowest, n = 50	Q2, n = 49	Q3, n = 49	Q4 highest, n = 50	p*
Folate biomarkers
RBC-folate, nmol/L	380 (346–409)	516 (475–554)	662 (628–718)	901 (817–1026)	–
Serum folate, nmol/L	12.1 (8.4–14.0)^a,b	12.7 (10.7–14.7)^c	18.8 (13.9–22.8)^a,c	20.4 (15.9–30.8)^b,c	.000
tHcy, µmol/L	7.7 (6.2–9.1)	7.3 (6.1–8.7)	6.8 (5.9–8.1)	7.2 (5.8–8.3)	.319
Dietary intakes‡
Folate intake, µg DFE/d	259 (216–314)	275 (235–367)	283 (235–376)	317 (223–378)	.193
Total energy intake, kcal/d	1728 (1591–2159)	1977 (1565–2312)	1808 (1574–2131)	1945 (1633–2210)	.527
Carbohydrate, g/d	199 (167–244)	226 (186–254)	203 (175–242)	210 (178–263)	.414
Fat, g/d	76 (64–87)	79 (61–98)	75 (58–86)	79 (65–91)	.644
Proteins, g/d	65 (58–79)	69 (55–87)	74 (56–85)	72 (61–84)	.721
Fibre, g/d	18.3 (15.3–22.8)^a,d,e	21.7 (17.3–26.9)^d	21.6 (17.9–24.8)^e	21.6 (17.4–30.9)^a	.012
Demographics
Age, years	23 (21–27)^a,f	27 (23–31)^a	26 (24–29)^f	25 (22–32)	.025
BMI, kg/m^2	21.5 (19.8–23.0)	21.5 (20.2–23)	21.7 (20.4– 23.0)	21.2 (19.8–23.2)	.892
Smokers, n (%)	10 (20)	10 (20.4)	6 (12.2)	7 (14.0)	.606†
Use hormonal contraceptives, n (%)	34 (68)	30 (61.2)	28 (57.1)	28 (56)	.606†
Practicing physical activity, n (%)	34 (68)	38 (77.6)	36 (73.5)	45 (90)	.058†
Women having children, n (%)	5 (10)	9 (18.4)	9 (18.4)	11 (22)	.436†
Education, n (%)					.298†
Less than university	18 (36)	16 (32.7)	9 (18.4)	12 (24)
University student	19 (38)	14 (28.6)	17 (34.7)	19 (38)
University degree or higher	13 (26)	19 (38.8)	23 (46.9)	19 (38)

Data are shown as median (25th–75th percentiles) or n (%).

* p values were determined with the use of Kruskall–Wallis test.

† p values were determined with the use of Chi-square test.

Pairwise comparisons were determined with two sided tests and Bonferroni correction.

^a–fGroups that carry similar letters are significantly different.

^a–cp < .05; ^dp = .065; ^ep = .091; ^fp = .077.

‡ The intake data are mean of two food protocols repeated within 8 weeks.

Concentrations of folate in serum and RBCs were measured by using IMMULITE 2000.

DFE: dietary folate equivalents; RBC: red blood cells; tHcy: total homocysteine.

Table 4. Folate intake and concentrations of RBC-folate and serum folate according to serum-folate in 198 young German women not receiving any folate supplements.

Serum folate, nmol/L	n	Serum folate, nmol/L	Folate intake, µg DFE/d^a	RBC-folate, nmol/L	RBC-folate ≥ 952 nmol/L, n (%)^d
< 7.0	7	5.9 (5.2–6.8)	295 (238–381)	250 (222–353)	0 (0)
7.1–11.0	35	9.5 (8.4–10.4)	251 (216–317)	444 (402–564)	1 (2.9)
11.1–15.0	60	13.1 (12.2–13.8)	271 (235–342)	507 (413–626)	3 (5.0)
15.1–19.0	35	17.0 (16.1–17.7)	281 (235–377)	649 (450–794)	3 (8.6)
19.1–23.0	27	20.6 (19.9–21.5)	272 (219–382)	684 (627–841)	3 (11.1)
> 23.0E	34	32.3 (25.4–40.8)	299 (251–377)	856 (682–981)	9 (26.5)
p^b	/	<.001	.426	<.001	.009^c

Data are median and (25th–75th percentiles) or n (%).

^aFolate intake was mean values of 2 × 3-days food protocols repeated within 8 weeks.

^bp values were determined with the use of Kruskall–Wallis test for continuous variables.

^cp values were determined with the use of Chi-square test for categorical variables.

^d% of women of the same category of serum folate.

DFE: dietary folate equivalents; RBC: red blood cells.

Table 5. Concentrations of folate markers in German young women according to lifestyle, demographic or dietary determinants.

	n	Serum folate, nmol/L	RBC-folate, nmol/L	tHcy, µmol/L
Folate intake, µg DFE/d
≥ 280	97	15.9 (12.6–21.5)	624 (479–794)	7.3 (6.1–8.7)
< 280	101	13.8 (11.1–19.0)	551 (428–711)	7.2 (6.1–8.3)
p^a		.029	.113	.631
Fiber intake, g/d
≥ 21.0	101	16.3 (12.6–22.3)	624 (491–792)	7.2 (6.0–8.4)
< 21.0	97	14.0 (10.5–18.7)	560 (402–737)	7.3 (6.1–8.6)
p^a		.004	.038	.790
Carbohydrate intake, g/d
≥ 210	97	15.4 (12.2–20.6)	591 (455–775)	7.3 (6.2–8.6)
< 210	101	14.0 (11.1–19.4)	588 (424–766)	7.1 (5.9–8.4)
p^a		.328	.851	.552
Age, years
≥ 25	115	15.2 (11.6–20.6)	605 (468–763)	7.1 (6.1–8.5)
< 25	83	14.5 (10.7–20.4)	547 (395– 790)	7.3 (6.0–8.4)
p^a		.400	.126	.903
Smoking
No	165	15.9 (12.1–21.4)	605 (442–779)	7.3 (6.1–8.4)
Yes	33	12.5 (10.0–16.1)	547 (402–696)	6.8 (5.7–8.6)
p^a		.003	.383	.420
Using hormone contraceptives
No	78	17.2 (12.7–21.5)	638 (463–837)	6.8 (5.7–9.1)
Yes	120	13.8 (11.1–19.2)	577 (421–748)	7.3 (6.2–8.3)
p^a		.016	.056	.337
Physically active
No	45	13.8 (10.7–18.6)	540 (396–665)	6.8 (5.7–8.5)
Yes	153	15.4 (11.4–20.6)	608 (455–794)	7.3 (6.1–8.4)
p^a		.177	.015	.264
Have children
No	164	14.5 (11.2–19.9)	579 (431–761)	7.3 (6.2–8.5)
Yes	34	15.9 (12.6–24.2)	621 (467–894)	6.5 (5.2–8.2)
p^a		.142	.081	.053
Education^c
High	74	15.6 (12.6–21.2)	628 (493–779)	7.3 (6.1–8.2)
Medium	69	15.0 (11.0–20.6)	605 (422–791)	7.3 (6.1–8.7)
Low	55	13.4 (10.7–20.4)	548 (409–734)	6.8 (5.8–8.7)
p^b		.300	.175	.641

Data are median (25–75th percentiles).

^a p values were determined with the use of Mann–Whitney test.

^b p values were determined with the use of Kruskal–Wallis test.

^c Education categories: high (university or higher), medium (university student), low (less than university).

^d DFE: dietary folate equivalents; RBC: red blood cells.

Table 6. Stepwise multiple linear regression analysis to predict dietary and lifestyle factors with significant influence on RBC-folate concentrations in 198 German women not receiving any supplement.

Dependent variable log (RBC-folate)	Variables with a significant effect in the final model	Beta coefficient (95%CI)	p
	Age (years)	0.0138 (0.0055,0.0221)	.0013
	Fibre intake (g/d)	0.0164 (0.0097,0.0232)	<.001
	Carbohydrates intake (g/d)	−0.0017 (−0.0027, −0.0007)	.0013

Independent variables entered in the model were: having children (1 = yes, 0 = no), smoking (1 = yes, 0 = no), using contraceptive hormones (1 = yes, 0 = no), physically active (1 = yes, 0 = no), education (low = 2, medium = 1, high = 0) (all as categorical variables) and age, BMI, folate intake, fibre intake, carbohydrate intake, fat intake and protein intake as continuous variables. Adjusted R² = 13.1%. CI: confidence intervals; RBC: red blood cells.

Bailey LB, Stover PJ, McNulty H, Fenech MF, Gregory JF III, Mills JL, Pfeiffer CM, Fazili Z, Zhang M, Ueland PM, et al. 2015. Biomarkers of nutrition for development-folate review. J Nutr. 145:1636S–1680S.

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