Association between the serum vitamin D level and prevalence of obesity/abdominal obesity in women with infertility: a cross-sectional study of the National Health and Nutrition Examination Survey data

Figures & data

Figure 1. Flowchart of participants included in analyses.

Table 1. Descriptions of study individuals’ characteristics.

Variables	N = 201
Age, (years) (%)	35.34 ± 0.54
20–30	54 (21.69)
31–40	92 (48.90)
>40	55 (29.41)
Race/ethnicity, %
Mexican American	65 (57.66)
Non-Hispanic white	49 (14.75)
Non-Hispanic Black	54 (18.12)
Other Race	33 (9.47)
Married/live with partner
Yes	141 (74.17)
No	60 (25.82)
Education level, %
Below high school	31 (11.92)
High School or above	170 (88.08)
Poverty income ratio^a, %
Poor	41 (12.94)
Not poor	160 (87.06)
Sleep hour (hour)	7.31 ± 0.11
PHQ-9	4.53 ± 0.46
Body mass index, kg/m²	31.70 ± 0.75
Obesityb (%)
Yes	113 (56.07)
No	88 (43.93)
Waist circumference, cm	102.17 ± 1.68
Abdominal Obesity^c (%)
Yes	145 (74.20)
No	56 (25.80)
Systolic blood pressure, (mmHg)	114.44 ± 0.96
Diastolic blood pressure, (mmHg)	70.39 ± 0.82
Smoking (%)
Yes	39 (19.27)
No	162 (80.73)
Alcohol use (%)
Yes	57 (24.04)
No	144 (75.96)
DM history (%)
Yes	22 (9.94)
No	179 (90.06)
Hypertension history (%)
Yes	51 (24.17)
No	150 (75.83)
Hyperlipidaemia history (%)
Yes	81 (38.43)
No	120 (61.57)
25(OH)D, (nmol/L)	61.05 ± 2.23

Continuous variables are presented as mean ± standard error (SE); Categorical variables are presented as counts (weighted percentage).

Abbreviation: PHQ-9, Patient Health Questionnaire‑9; DM, diabetes mellitus; 25(OH)D, 25 hydroxy vitamin D3.

^aPoverty income ratio for not poor was defined as ≥ 1, and for poor was defined as < 1.

^bObesity was defined as when body mass index ≥30 kg/m².

^cAbdominal obesity was defined as when waist circumference ≥88 cm.

Table 2. Linear regression analysis between vitamin D and study variables.

Variables	Univariate		Multivariate^b
	β (95% CI)	P value	β (95% CI)	P value
Age, (years)
20–30	Ref		Ref
31–40	14.41 (5.39, 23.43)	0.002	5.51 (−3.40, 14.43)	0.224
>40	14.06 (3.72, 24.41)	0.008	4.69 (−5.76, 15.13)	0.377
Race/ethnicity
Mexican American	Ref
Non-Hispanic white	−28.90 (−38.18, −19.62)	<0.001	−27.18 (−35.85, −18.52)	<0.001
Non-Hispanic Black	−25.01 (−32.95, −17.07)	<0.001	−22.37 (−29.99, −14.76)	<0.001
Other Race	−12.28 (−21.59, −2.98)	0.010	−15.18 (−25.00, −5.36)	0.003
Married/live with partner
Yes	Ref		–	–
No	−4.74 (−14.62, 5.15)	0.345	–	–
Education level
Below high school	Ref		Ref
High School or above	13.35 (4.76, 21.94)	0.002	4.22 (−4.37, 12.82)	0.333
Poverty income ratio^a
Poor	Ref		Ref
Not poor	12.04 (3.41, 20.66)	0.006	−4.50 (−12.81, 3.82)	0.288
Sleep hour (hour)	0.25 (−2.41, 2.90)	0.855	–	–
PHQ-9	−0.62 (−1.39, 0.15)	0.112	–	–
Body mass index, kg/m²	−0.96 (−1.40, −0.51)	<0.001	–	–
Obesity ^a
Yes	−17.65 (−26.31, −8.98)	<0.001	−17.89 (−30.69, −5.09)	0.006
No	Ref		Ref
Waist circumference, cm	−0.40 (−0.59, −0.22)	<0.001	–	–
Abdominal Obesity^a
Yes	−9.63 (−20.24, 0.32)	0.057	3.56 (−11.34, 18.46)	0.638
No	Ref		Ref
Systolic blood pressure, (mmHg)	−0.22 (−0.55, 0.11)	0.182	–	–
Diastolic blood pressure, (mmHg)	0.23 (−0.22, 0.69)	0.313	–	–
Smoking
Yes	−3.61 (−14.37, 7.16)	0.509	–	–
No	Ref		–	–
Alcohol use
Yes	1.45 (−8.40, 11.30)	0.772	–	–
No	Ref		–	–
DM history
Yes	−0.73 (−20.80, 3.34)	0.155	–	–
No	Ref		–	–
Hypertension history
Yes	1.58 (−8.91, 12.07)	0.767	–	–
No	Ref		–	–
Hyperlipidaemia history
Yes	−6.16 (−15.40, 3.07)	0.189	–	–
No	Ref		–	–

^a The definition of parameters were the same as in Table 1.

^b The parameters adjusted in multivariable linear regression included age, race/ethnicity, education level, Poverty income ratio, obesity and abdominal obesity. (entered).

Figure 2. Multivariable-adjusted spline curves for serum vitamin D levels about obesity (a) and abdominal obesity (b) as assessed by a spline regression model. (Solid lines—OR, dashed lines—95% CI) The model was adjusted for age (20–30, 31–40 and >40 years), race (Mexican American, Non-Hispanic white, Non-Hispanic Black and other race), education level (below high school and high school or above), and poverty income ratios (poor and not poor). P Nonlinear > 0.05 implies a significant linear relationship.

Table 3. Association between serum vitamin D quartiles and obesity/abdominal obesity.

25(OH)D, (nmol/L)	Total No.	No. of cases (%)	Model 1 Odds ratio (95% confidence interval)	Model 2 Odds ratio (95% confidence interval)	Model 3 Odds ratio (95% confidence interval)
Obesity
Q1	51	38 (74.51)	5.197 (2.211–12.212)	5.285 (2.201–12.687)	8.290 (2.451–28.039)
Q2	50	29 (58.00)	2.455 (1.097–5.494)	2.588 (1.119–5.985)	3.722 (1.253–11.055)
Q3	50	28 (56.00)	2.263 (1.013–5.052)	2.338 (1.026–5.332)	3.252 (1.174–9.025)
Q4	50	18 (36.00)	Ref	Ref	Ref
p for trend			<0.001	<0.001	0.001
Abdominal obesity
Q1	51	44 (86.27)	3.853 (1.445–10.274)	4.259 (1.537–11.799)	4.820 (1.351–17.194)
Q2	50	34 (68.00)	1.302 (0.571–2.969)	1.583 (0.660–3.796)	1.683 (0.578–4.905)
Q3	50	36 (72.00)	1.576 (0.680–3.654)	1.806 (0.750–4.346)	2.150 (0.768–6.017)
Q4	50	31 (62.00)	Ref	Ref	Ref
p for trend			0.016	0.010	0.037

Model 1, Unadjusted;

Model 2, Adjusted for age (20–30, 31–40 and >40 years);

Model 3, Model 2 plus additional adjustment for the race, married/live with partner status, education level, poverty income ratios, sleep hours, PHQ-9, smoking status, alcohol use and disease histories (including DM, hypertension and hyperlipidaemia).