Soy isoflavone intake and the likelihood of ever becoming a mother: the Adventist Health Study-2

Figures & data

Table 1 Relationships between soy isoflavone intake and some variables relevant to isoflavone intake and reproduction in the Adventist Health study-2

	Soy isoflavone intake (mg per day)						P for trend
	0–9	10–19	20–29	30–39	40–49	≥50
Number of women	6,089	1,968	1,376	812	529	914	–
Isoflavone intake (mg/day)	3.7 (2.9)	14.7 (3.1)	24.6 (2.9)	34.5 (2.9)	44.8 (2.9)	79.3 (32.5)	–
Age at enrollment	42.0 (5.3)	42.1 (5.3)	41.9 (5.4)	42.0 (5.4)	41.8 (5.3)	41.6 (5.6)	0.04
% never married	13.1 (798)	10.9 (215)	11.9 (164)	10.3 (84)	11.5 (61)	14.2 (130)	0.6
% with college	46.5 (2,833)	54.5 (1,072)	56.8 (781)	55.4 (450)	56.3 (298)	59.2 (541)	<0.001
% Black	35.3 (2,134)	32.8 (640)	29.5 (402)	28.0 (226)	33.9 (178)	37.4 (338)	0.2
Age at menarche	12.41 (1.54)	12.37 (1.49)	12.39 (1.51)	12.49 (1.52)	12.46 (1.51)	12.40 (1.53)	0.6
% used OCs	77.3 (4,694)	76.6 (1,502)	74.8 (1,023)	70.7 (571)	69.8 (368)	65.9 (599)	<0.001
% extended OC use*	3.4 (206)	2.0 (39)	1.5 (20)	1.6 (13)	1.1 (6)	1.0 (9)	<0.001
% never pregnant	17.9 (1,089)	19.6 (385)	18.8 (258)	20.3 (165)	19.1 (101)	22.3 (204)	0.002
% nulliparous	24.7 (1,506)	25.7 (506)	25.9 (357)	26.5 (215)	26.1 (138)	29.7 (271)	0.003
% problems becoming pregnant	17.1 (1,032)	16.1 (315)	17.8 (243)	16.4 (132)	15.7 (82)	15.6 (141)	0.3
Parity in all women	1.69 (1.27)	1.67 (1.29)	1.60 (1.21)	1.67 (1.31)	1.61 (1.25)	1.54 (1.27)	<0.001
Parity in parous women	2.24 (0.95)	2.24 (0.97)	2.17 (0.87)	2.27 (0.97)	2.18 (0.95)	2.19 (0.93)	0.09
Age at first delivery	25.7 (5.2)	26.3 (4.9)	26.5 (5.0)	26.5 (5.0)	26.8 (5.2)	27.0 (5.3)	<0.001
% ever smoked	7.0 (426)	4.6 (91)	4.7 (65)	3.7 (30)	4.9 (26)	4.3 (39)	<0.001
% ever used alcohol	38.4 (2,327)	27.1 (533)	27.6 (379)	26.6 (216)	28.0 (148)	25.9 (235)	<0.001
Physical activity (times/week)	2.2 (1.9)	2.4 (1.9)	2.5 (1.9)	2.7 (1.9)	2.6 (1.9)	2.6 (1.9)	<0.001
BMI (kg/m^2) at age 20	21.6 (3.8)	21.3 (3.4)	21.4 (3.6)	21.3 (3.7)	21.3 (3.7)	21.4 (4.1)	0.002
% with monthly use of caffeinated drinks	49.3 (2,956)	32.8 (633)	27.6 (375)	21.7 (173)	19.8 (102)	17.5 (157)	<0.001
% vegetarians	37.6 (2,292)	63.6 (1,252)	71.6 (985)	77.7 (631)	76.6 (405)	76.5 (699)	<0.001
% vegans	2.1 (125)	7.0 (137)	10.7 (147)	15.4 (125)	17.8 (94)	18.7 (171)	<0.001
Vegetarian meat analogs (g/day)	37 (38)	62 (56)	66 (64)	66 (58)	69 (73)	81 (81)	<0.001
Tofu/soybean products (g/day)	3 (4)	12 (12)	24 (19)	38 (23)	49 (30)	91 (74)	<0.001
Soy milk (g/day)	9 (29)	74 (79)	120 (112)	153 (139)	210 (171)	380 (333)	<0.001
Energy intake (kcal per day)	1,736 (702)	1,890 (689)	1,980 (687)	2,090 (702)	2,267 (721)	2,506 (788)	<0.001

Notes:

* Used OCs for 7 or more years both when aged 20–29 years and when aged 30–39 years. Data given as percentages (n) or mean (SD)Abbreviations: SD, standard deviation; OC, oral contraceptives; BMI, body mass index.

Table 2 Associations between soy isoflavone intake (mg per day) and fertility (at least one live child) estimated at age 26 years in the Adventist Health Study-2

Isoflavone intake (mg/day)	Number of women/parous women	Hazard ratio (95% CI) at age 26 years
<10	2,281/1,569	1.0
10–19	742/512	0.92 (0.83, 1.02)
20–29	526/358	0.93 (0.84, 1.04)
30–39	320/220	0.86 (0.74, 1.00)
40–49	221/152	0.93 (0.78, 1.10)
50+	386/259	0.83 (0.72, 0.96)
All	4,476/3,070
P-value for linear trend		0.003

Notes: Adjusted for educational level and marital status. Women aged 30–40 years when completing the lifestyle questionnaire.

Abbreviation: CI, confidence interval.

Table 3 Associations between soy isoflavone intake (mg per day) and fertility (at least one live child) in the Adventist Health Study-2

Isoflavone intake (mg/day)	Number of women/parous women	Estimated relative risk (95% CI) for giving birth to at least one live child
<10	3,808/3,014	1.0
10–19	1,226/950	0.99 (0.96, 1.02)
20–29	850/661	0.99 (0.96, 1.02)
30–39	492/377	0.97 (0.93, 1.02)
40–49	308/239	0.98 (0.93, 1.03)
50+	528/384	0.96 (0.92, 1.01)
All	7,212/5,625
P-value for linear trend		0.05

Notes: Adjusted for age when completing the lifestyle questionnaire, educational level and marital status. Women aged 41–50 years when completing the lifestyle questionnaire.

Abbreviation: CI, confidence interval.

Table 4 Associations between soy isoflavone intake (mg per day) and never having been pregnant in the Adventist Health Study-2

Isoflavone intake (mg/day)	Number of women/never pregnant women	Estimated relative risk (95% CI) for never been pregnant
<10	3,808/558	1.0
10–19	1,226/208	1.14 (1.03, 1.26)
20–29	850/129	0.98 (0.86, 1.12)
30–39	492/85	1.10 (0.95, 1.27)
40–49	308/52	1.11 (0.92, 1.33)
50+	528/103	1.15 (1.02, 1.29)
All	7,212/1,135
P-value for linear trend		0.03

Notes: Adjusted for age when completing the lifestyle questionnaire, educational level, and marital status. Women aged 41–50 when completing the lifestyle questionnaire.

Abbreviation: CI, confidence interval.