Association between urinary cobalt exposure and kidney stones in U.S. adult population: results from the National Health and Nutrition Examination Survey

Figures & data

Figure 1. Schematic flow diagram of inclusion and exclusion criteria for our study cohort.

Table 1. Baseline characteristics of NHANES participants between 2007 and 2016 (n = 8518).^a

Characteristic	Total	None-stone formers	Stone formers	p Value
	No. (%)	No. (%)	No. (%)
Total patients	8518	7699 (90.4)	819 (9.6)
Gender				<0.001
Male	4220 (49.5)	3741 (48.6)	479 (58.5)
Female	4298 (50.5)	3958 (51.4)	340 (41.5)
Age				<0.001
<50 years	4415 (51.8)	4141 (53.8)	274 (33.5)
≥50 years	4103 (48.2)	3558 (46.2)	545 (66.5)
Race				<0.001
Non-Hispanic White	3588 (42.1)	3136 (40.7)	452 (55.2)
Non-Hispanic Black	1707 (20.0)	1616 (21.0)	91 (11.1)
Mexican American	1328 (15.6)	1223 (15.9)	105 (12.8)
Other Hispanic	946 (11.1)	842 (10.9)	104 (12.7)
Other	949 (11.1)	882 (11.5)	67 (8.2)
Education level				0.284
Less than high school	2181 (25.6)	1954 (25.4)	227 (27.7)
High school or equivalent	1897 (22.3)	1713 (22.2)	184 (22.5)
College or above	4440 (52.1)	4032 (52.4)	408 (49.8)
Marital status				<0.001
Married	4428 (52.0)	3947 (51.3)	481 (58.7)
Unmarried	4090 (48.0)	3752 (48.7)	338 (41.3)
BMI (kg/m^2)				<0.001
<25.0	2497 (29.3)	2326 (30.2)	171 (20.9)
≥25.0	6021 (70.7)	5373 (69.8)	648 (79.1)
Hypertension				<0.001
Yes	2977 (34.9)	2573 (33.4)	404 (49.3)
No	5541 (65.1)	5126 (66.6)	415 (50.7)
Diabetes				<0.001
Yes	1063 (12.5)	882 (11.5)	181 (22.1)
No	7261 (85.2)	6651 (86.4)	610 (74.5)
Borderline	194 (2.3)	166 (2.2)	28 (3.4)
Vigorous recreational activities				<0.001
Yes	1852 (21.7)	1735 (22.5)	117 (14.3)
No	6666 (78.3)	5964 (77.5)	702 (85.7)
Moderate recreational activities				0.242
Yes	3407 (40.0)	3095 (40.2)	312 (38.1)
No	5111 (60.0)	4604 (59.8)	507 (61.9)
Blood urea nitrogen	13.43, 5.74	13.28, 5.60	14.88, 6.76	<0.001
Creatinine	1.02, 0.33	1.01, 0.32	1.05, 0.36	0.007
Uric acid	5.46, 1.47	5.43, 1.46	5.71, 1.55	<0.001
eGFR	94.48, 23.65	95.37, 23.47	86.14, 23.73	<0.001
Urine creatinine	118.22, 76.90	117.68, 77.23	123.26, 73.59	0.048

^aFor categorical variables, p values were analyzed by χ² tests. For continuous variables, the t-test for slope was used in generalized linear models.

BMI: body mass index; eGFR: estimated glomerular filtration rate.

Figure 2. Relative risk for kidney stones based on U-Cd and U-Co level before PSM. The shaded areas represent upper and lower 95% CIs. Adjustment factors are as same as which presented in extended model 4. Restricted cubic spline (RCS) plot of the association between log2-transformed U-Cd/U-Cr and U-Co/U-Cr levels and kidney stones. The solid and dashed lines represent the odds ratios and 95% confidence intervals. (A) U-Cd; (B) U-Co; (C) log2-transformed U-Cd/U-Cr; (D) log2-transformed U-Co/U-Cr.

Figure 3. Adjusted odds ratios for associations between the U-Cd and U-Co and the presence of kidney stones in NHANES 2007–2016 before PSM. (A) U-Cd; (B) U-Co.

Figure 4. Distribution of propensity score before and after matching.

Table 2. Adjusted odds ratios for associations between the heavy metals and the presence of kidney stone in NHANES 2007–2016 before PSM.^a

Heavy metals		Model 1	Model 2	Model 3	Model 4
	N	aOR (95% CI)	aOR (95% CI)	aOR (95% CI)	aOR (95% CI)
U-Cd
Q1	2127	Reference	Reference	Reference	Reference
Q2	2134	1.732 (1.384–2.167)	1.582 (1.259–1.989)	1.553 (1.235–1.954)	1.483 (1.172–1.878)
Q3	2128	1.521 (1.210–1.912)	1.353 (1.069–1.714)	1.309 (1.033–1.660)	1.216 (0.945–1.565)
Q4	2129	2.168 (1.745–2.694)	1.862 (1.482–2.341)	1.863 (1.481–2.343)	1.663 (1.277–2.167)
p for trend		<0.001	<0.001	<0.001	<0.001
U-Co
Q1	2133	Reference	Reference	Reference	Reference
Q2	2125	1.219 (0.982–1.513)	1.211 (0.981–1.520)	1.199 (0.962–1.495)	1.196 (0.959–1.491)
Q3	2127	1.334 (1.079–1.650)	1.363 (1.098–1.692)	1.337 (1.075–1.661)	1.346 (1.083–1.673)
Q4	2133	1.534 (1.246–1.887)	1.770 (1.433–2.188)	1.742 (1.408–2.156)	1.748 (1.412–2.164)
p for trend		0.001	<0.001	<0.001	<0.001

^a Adjusted covariates: Model 1: univariate analysis; Model 2: age, gender, race, education levels, and marital status; Model 3: Model 2 plus BMI, hypertension, diabetes, vigorous recreational activities, and moderate recreational activities; Model 4: Model 3 plus blood urea nitrogen, creatinine, uric acid, eGFR, and urine creatinine.

CI: confidence interval; aOR: adjusted odds ratio; BMI: body mass index; eGFR: estimated glomerular filtration rate; PSM: propensity score matching

Figure 5. Relative risk for kidney stones based on U-Cd and U-Co level after PSM. The shaded areas represent upper and lower 95% CIs. Adjustment factors are as same as which presented in extended model 4. Restricted cubic spline (RCS) plot of the association between log2-transformed U–Cd/UCr and U–Co/UCr levels and kidney stones. The solid and dashed lines represent the odds ratios and 95% confidence intervals. (A) U-Cd; (B) U-Co; (C) log2-transformed U-Cd/U-Cr; (D) log2-transformed U-Co/U-Cr.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.