Association Between Composite Dietary Antioxidant Index and the Risk of Endometriosis-Related Rheumatoid Arthritis in Women of Childbearing Age: A Cross-Sectional Study Based on the National Health and Nutrition Examination Survey Database

Figures & data

Table 1 The Basic Information of the Included Study Population

Variables	Total (n=3803)	EM		Statistics	P
		No (n=3621)	Yes (n=182)
Age, year, Mean (S.E)	31.68 (0.17)	31.49 (0.18)	34.56 (0.49)	t=−6.06	<0.001
Race, n (%)				χ^2=47.588	<0.001
White	1718 (65.75)	1595 (64.59)	123 (83.36)
Black	734 (12.36)	706 (12.68)	28 (7.53)
Other	1351 (21.89)	1320 (22.73)	31 (9.11)
Education, n (%)				χ^2=6.090	0.048
Middle school	887 (14.94)	868 (15.35)	19 (8.71)
High School	818 (22.34)	775 (21.89)	43 (29.16)
University	2098 (62.72)	1978 (62.76)	120 (62.13)
Marital status, n (%)				χ^2=10.253	0.001
Married	1420 (38.20)	1372 (38.97)	48 (26.61)
Unmarried	2383 (61.80)	2249 (61.03)	134 (73.39)
PIR, n (%)				χ^2=1.535	0.215
<5	2938 (76.13)	2809 (76.43)	129 (71.61)
≥5	865 (23.87)	812 (23.57)	53 (28.39)
Drinking status, n (%)				χ^2=0.831	0.842
No	1481 (31.24)	1422 (31.47)	59 (27.75)
<1 time/week	1374 (38.20)	1304 (38.21)	70 (38.09)
≥1 time/week	729 (25.53)	688 (25.33)	41 (28.70)
Unknown	219 (5.02)	207 (4.99)	12 (5.46)
Smoking status, n (%)				χ^2=1.583	0.208
No	2501 (60.59)	2389 (60.96)	112 (54.96)
Yes	1302 (39.41)	1232 (39.04)	70 (45.04)
Physical activity, n (%)				χ^2=0.652	0.722
<450	818 (22.45)	774 (22.49)	44 (21.82)
≥450	1570 (48.06)	1482 (47.86)	88 (51.09)
Unknown	1415 (29.49)	1365 (29.65)	50 (27.09)
Age at menarche, ages, n (%)				χ^2=0.848	0.654
<=12	1881 (47.25)	1784 (46.99)	97 (51.11)
12–14	1431 (39.39)	1365 (39.56)	66 (36.77)
>14	491 (13.36)	472 (13.45)	19 (12.11)
Gravidity, n (%)				χ^2=9.738	0.008
No	156 (4.77)	140 (4.42)	16 (10.13)
Yes	1941 (48.86)	1851 (48.82)	90 (49.49)
Unknown	1706 (46.37)	1630 (46.76)	76 (40.37)
Uterine fibroids, n (%)				χ^2=30.491	<0.001
No	3548 (92.94)	3410 (93.80)	138 (79.81)
Yes	255 (7.06)	211 (6.20)	44 (20.19)
Surgery, n (%)				χ^2=86.417	<0.001
No	3717 (96.95)	3561 (97.92)	156 (82.22)
Yes	86 (3.05)	60 (2.08)	26 (17.78)
Pregnancy status, n (%)				χ^2=1.841	0.398
No	1904 (58.32)	1815 (58.42)	89 (56.79)
Yes	895 (7.63)	862 (7.78)	33 (5.29)
Unknown	1004 (34.05)	944 (33.79)	60 (37.92)
Diabetes, n (%)				χ^2=3.954	0.047
No	3681 (97.14)	3502 (97.02)	179 (98.99)
Yes	122 (2.86)	119 (2.98)	3 (1.01)
Hypertension, n (%)				χ^2=1.162	0.281
No	3043 (78.43)	2912 (78.69)	131 (74.58)
Yes	760 (21.57)	709 (21.31)	51 (25.42)
Dyslipidemia, n (%)				χ^2=2.147	0.143
No	1786 (52.46)	1708 (52.81)	78 (47.08)
Yes	2017 (47.54)	1913 (47.19)	104 (52.92)
Female hormones use, n (%)				χ^2=34.404	<0.001
No	3570 (92.15)	3424 (93.00)	146 (79.32)
Yes	233 (7.85)	197 (7.00)	36 (20.68)
Family history of arthritis, n (%)				χ^2=5.073	0.024
No	403 (12.80)	376 (12.45)	27 (18.21)
Yes	3400 (87.20)	3245 (87.55)	155 (81.79)
BMI, kg/m^2, n (%)				χ^2=2.268	0.132
<25	2397 (55.54)	2293 (55.92)	104 (49.75)
≥25	1406 (44.46)	1328 (44.08)	78 (50.25)
Energy, kcal, Mean (S.E)	2016.09 (18.39)	2017.55 (19.19)	1993.88 (65.58)	t=0.35	0.731
Protein, gm, Mean (S.E)	73.48 (0.75)	73.76 (0.79)	69.18 (2.23)	t=1.90	0.062
Carbohydrate, gm, Mean (S.E)	255.11 (2.35)	255.03 (2.38)	256.34 (9.62)	t=−0.13	0.893
Total fat, gm, Mean (S.E)	75.32 (0.91)	75.42 (0.96)	73.81 (2.71)	t=0.55	0.588
CDAI, n (%)				χ^2=0.785	0.376
<Q2	1864 (51.90)	1770 (51.66)	94 (55.54)
≥Q2	1939 (48.10)	1851 (48.34)	88 (44.46)
RA, n (%)				χ^2=6.557	0.010
No	3729 (98.01)	3559 (98.22)	170 (94.77)
Yes	74 (1.99)	62 (1.78)	12 (5.23)
CDAI: EM, n (%)
≥Q2: No	1851 (45.35)	1851 (48.34)	0 (0.00)
≥Q2: Yes	88 (2.75)	0 (0.00)	88 (44.46)
<Q2: No	1770 (48.46)	1770 (51.66)	0 (0.00)
<Q2: Yes	94 (3.44)	0 (0.00)	94 (55.54)

Note: Q₂, Median (−0.65).

Abbreviations: EM, endometriosis; PIR, poverty-to-income ratio; BMI, body mass index; CDAI, Composite Dietary Antioxidant Index; RA, rheumatoid arthritis; t, t-test; χ², chi-square test; SD, standard deviation; M, Median.

Figure 1 A diagram flow describing the patients’ selection. NHANES, National Health and Nutrition Examination Survey.

Table 2 Association of CDAI, and EM with the Risk of RA

CDAI	Model 1		Model 2
	OR (95% CI)	P	OR (95% CI)	P
≥Q2	Ref		Ref
<Q2	1.99 (1.18–3.35)	0.011	1.85 (1.12–3.04)	0.015
EM	OR (95% CI)	P	OR (95% CI)	P
No	Ref		Ref
Yes	3.05 (1.22–7.60)	0.018	3.05 (1.19–7.81)	0.023

Notes: Q₂, Median (−0.65); Model 1 was not adjusted for any confounders. Age, drinking status, smoking status, pregnancy status, and diabetes were adjusted in Model 2.

Abbreviations: EM, endometriosis; CDAI, Composite Dietary Antioxidant Index; RA, rheumatoid arthritis; OR, odds ratio; CI, confidence interval; Ref, reference.

Table 3 The Interaction Between CDAI and EM on the Risk of RA

CDAI: EM	Model 1	P	Model 2	P
	OR (95% CI)		OR (95% CI)
≥Q2: No	Ref		Ref
≥Q2: Yes	0.87 (0.19–4.03)	0.859	0.90 (0.19–4.18)	0.869
<Q2: No	1.65 (0.92–2.96)	0.091	1.53 (0.87–2.70)	0.127
<Q2: Yes	6.82 (2.52–18.50)	<0.001	6.19 (2.33–16.43)	<0.001
P of trend	/	0.006	/	0.007

Notes:Q₂, Median (−0.65); Model 1 was not adjusted for any confounders. Age, drinking status, smoking status, pregnancy status, and diabetes were adjusted in Model 2.

Abbreviations: EM, endometriosis; CDAI, Composite Dietary Antioxidant Index; RA, rheumatoid arthritis; OR, odds ratio; CI, confidence interval; Ref, reference.

Table 4 Evaluations of the Additive Interaction Results

Indicators	Model 1
	RERI (95% CI)	AP (95% CI)	S(95% CI)
CDAI: EM	−1.012(−7.799–5.774)	−0.230(−2.151–1.691)	0.771(0.101–5.875)
	Model 2
	RERI (95% CI)	AP (95% CI)	S(95% CI)
CDAI: EM	−0.018(−7.661–7.624)	−0.003(−1.593–1.586)	0.995(0.135–7.334)

Notes: Q₂, Median (−0.65); Model 1 was not adjusted for any confounders. Age, drinking status, smoking status, pregnancy status, and diabetes were adjusted in Model 2.

Abbreviations: EM, endometriosis; CDAI, Composite Dietary Antioxidant Index; RA, rheumatoid arthritis; RERI, relative excess risk due to interaction; AP, attributable proportion due to interaction; S, synergy index; CI, confidence interval; Ref, reference.

Table 5 Coexistence of CDAI and EM on the Risk of RA

CDAI	Endometriosis	Model 1		Model 2
		OR (95% CI)	P	OR (95% CI)	P
<Q2	No	Ref		Ref
	Yes	4.13 (1.45–11.79)	0.009	3.94 (1.35–11.51)	0.013
≥Q2	No	Ref		Ref
	Yes	0.87 (0.19–4.02)	0.859	0.90 (0.19–4.35)	0.894

Notes: Q₂, Median (−0.65); Model 1 was not adjusted for any confounders. Age, drinking status, smoking status, pregnancy status, and diabetes were adjusted in Model 2.

Abbreviations: EM, endometriosis; CDAI, Composite Dietary Antioxidant Index; RA, rheumatoid arthritis; OR, odds ratio; CI, confidence interval; Ref, reference.