Serum vitamin C levels and their correlation with chronic kidney disease in adults: a nationwide study

Figures & data

Figure 1. A flowchart showing the sample selection from NHANES 2017–2018.

Table 1. Baseline characteristics of participants (n = 4969) according to vitamin C (quartiles 1–4, umol/L).

	Total (n = 4969)	Quartiles 1 (<30.4) (n = 1242)	Quartiles 2(30.4–50.3) (n = 1236)	Quartiles 3 (50.3–67.6) (n = 1239)	Quartiles 4 (≥67.6) (n = 1252)	p
Age (years)	47.5 ± 17.7	46.2 ± 16.8	45.8 ± 17.1	46.6 ± 17.2	51.3 ± 18.8	<.001
18–44	45.0 (43.0–47.1)	46.6 (42.5–50.7)	49.9 (45.7–54.1)	47.8 (43.5–52.1)	36.6 (32.7–40.6)
45–64	26.7 (24.8–28.8)	28.5 (24.6–32.7)	26.0(22.1–30.2)	26.6 (22.7–30.8)	25.9 (22.1–30.1)
65–80	28.2 (26.4–30.1)	25.0 (21.7–28.5)	24.1 (20.7–27.8)	25.7 (22.2–29.5)	37.5 (33.7–41.5)
Urine protein (mg/L)	38.1 ± 278.6	61.0 ± 392.8	46.2 ± 353.7	25.4 ± 182.6	21.4 ± 69.8	<.001
UACR (mg/g)	35.6 ± 269.5	55.2 ± 374.6	40.9 ± 291.2	23.8 ± 246.4	23.7 ± 88.0	.007
SCr (umol/L)	77.7 ± 28.3	81.4 ± 41.0	79.9 ± 27.6	76.3 ± 19.8	73.7 ± 19.0	<.001
eGFR (ml/min/1.73 m^2)	94.2 ± 22.3	93.9 ± 22.6	94.6 ± 23.0	96.5 ± 21.2	91.8 ± 22.2	<.001
HbA1C (%)	5.7 ± 0.9	5.8 ± 1.1	5.7 ± 0.9	5.6 ± 0.8	5.6 ± 0.8	<0.001
hs-CRP (mg/L)	3.8 ± 7.7	5.2 ± 9.7	4.2 ± 9.5	3.2 ± 5.5	2.8 ± 4.7	<.001
BUN (mmol/L)	5.3 ± 1.9	5.2 ± 2.1	5.3 ± 1.8	5.3 ± 1.7	5.4 ± 1.9	.004
SUA (umol/L)	320.2 ± 85.2	328.5 ± 88.5	332.0 ± 89.6	323.8 ± 82.7	298.4 ± 76.1	<.001
Hb (g/dL)	14.2 ± 1.5	14.4 ± 1.6	14.3 ± 1.5	14.2 ± 1.5	14.0 ± 1.3	<.001
TC (mmol/L)	4.9 ± 1.0	4.9 ± 1.1	4.9 ± 1.1	4.8 ± 1.0	4.9 ± 1.0	.008
HDL (mmol/L)	1.4 ± 0.4	1.3 ± 0.4	1.3 ± 0.4	1.4 ± 0.4	1.5 ± 0.4	<.001
Diabetes (%)						<.001
Yes	15.0 (13.6–16.5)	18.4 (15.5–21.8)	15.7 (13.1–18.8)	13.6 (11.1–16.6)	12.3 (10.0–15.1)
Hypertension (%)						<.001
Yes	51.3 (49.2–53.4)	56.8 (52.6–60.9)	54.7 (50.5–58.9)	46.9 (42.6–51.2)	47.4 (43.3–51.5)
LDL-C(%)						<.001
Yes	3.8 (3.1–4.7)	3.9 (2.6–5.9)	4.6 (3.1–6.6)	2.9 (1.9–4.6)	3.8(2.4–6.0)
Dietary VC intake by food,(mg/d)						<.001
<25.6	24.3 (22.5–26.2)	45.6 (41.5–49.8)	22.5 (19.1–26.3)	16.6 (13.8–19.8)	12.9 (10.3–16.1)
25.6–56.7	24.1 (22.3–26.0)	27.7 (24.2–31.5)	27.7 (24.0–31.8)	21.7 (18.3–25.5)	19.8 (16.7–23.4)
56.7–106.7	22.8 (21.1–24.7)	13.9 (11.3–17.1)	26.6 (22.9–30.6)	23.1 (19.6–27.0)	27.9 (24.3–31.8)
≥106.7	22.4 (20.6–24.2)	7.3 (5.5–9.5)	16.5 (13.9–19.5)	32.2 (28.1–36.5)	32.4 (28.6–36.3)
Not recorded	6.4 (5.6–7.4)	5.5 (3.9–7.7)	6.7 (5.3–8.4)	6.5 (4.9–8.6)	7.0 (5.4–9.1)
Daily dose of VC supplements, mg						<.001
None	63.5 (61.4–65.5)	87.3 (83.8–90.0)	69.2 (65.1–73.1)	59.1 (54.7–63.4)	39.9 (35.9–44.0)
1–60	11.5 (10.1–12.9)	7.1 (5.0–10.2)	12.5 (10.1–15.5)	14.4 (11.4–18.0)	11.7 (9.4–14.5)
61–120	11.6 (10.3–13.1)	3.4 (2.1–5.5)	10.6 (8.2–13.6)	14.2 (11.2–17.7)	17.9 (14.9–21.3)
121–500	7.7 (6.6–9.0)	1.2 (0.7–2.2)	5.8 (3.7–8.8)	7.3 (5.4–9.9)	16.1 (13.1–19.6)
≥500	5.8 (4.8–6.9)	1.0 (0.5–2.1)	1.9 (1.1–3.4)	5.0 (3.5–7.3)	14.5 (11.7–17.8)
Gender (%)						<.001
Male	48.9 (46.7–51.0)	56.6 (52.5–60.6)	54.3 (50.1–58.4)	53.3 (49.0–57.6)	32.3 (28.5–36.3)
Female	51.2 (49.0–53.3)	43.4 (39.4–47.6)	45.7 (41.6–49.9)	46.7 (42.5–51.0)	67.7 (63.7–71.5)
Race (%)						<.001
Hispanic	16.3 (15.2–17.5)	11.9 (10.1–14.0)	22.1 (19.5–25.0)	17.5 (15.3–20.0)	14.4 (12.4–16.6)
Non-Hispanic White	62.7 (60.9–64.5)	67.9 (64.6–71.1)	51.6 (47.4–55.7)	60.7 (56.9–64.4)	69.3 (66.2–72.3)
Non-Hispanic Black	10.6 (9.8–11.4)	10.9 (9.5–12.5)	13.4 (11.6–15.3)	10.3 (8.9–12.0)	8.0 (6.8–9.5)
Non-Hispanic Asian	5.6 (5.2–6.1)	3.4 (2.7–4.2)	7.2 (6.1–8.6)	6.2 (5.3–7.3)	5.8 (4.9–6.9)
Other races	4.8 (4.0–5.8)	6.0 (4.3–8.2)	5.7 (3.9–8.4)	5.3 (3.6–7.6)	2.4 (1.5–3.8)
Education						<.001
Less than high school	11.5 (10.6–12.6)	14.5 (12.4–17.0)	13.4 (11.4–15.7)	9.5 (8.0–11.3)	9.0 (7.5–10.8)
High school or equivalent	28.0 (26.1–29.9)	35.7 (31.7–39.8)	27.5 (23.8–31.5)	26.0 (22.4–29.9)	22.9 (19.7–26.5)
More than high school	60.4 (58.4–62.4)	49.8 (45.7–54.0)	58.9 (54.8–62.9)	64.5(60.4–68.3)	68.1 (64.3–71.6)
Not recorded	0.1 (0.0–0.2)	–	0.2 (0.1–0.6)	0.1 (0.0–0.2)	0.0(0.0–0.2)
Poverty-income ratio						<.001
<1.3	18.4 (17.2–19.8)	22.9 (20.2–25.7)	20.0 (17.2–23.1)	16.3 (14.0–19.0)	14.9 (12.8–17.4)
1.3–1.8	8.4 (7.6–9.3)	10.0 (8.3–12.1)	8.3 (6.6–10.3)	8.2 (6.7–10.1)	7.0 (5.7–8.6)
≥1.8	62.8 (60.9–64.6)	57.0 (53.1–60.8)	59.5 (55.5–63.4)	66.6 (62.9–70.1)	67.3 (63.8–70.7)
Not recorded	10.4 (9.3–11.7)	10.1 (8.1–12.6)	12.2 (9.7–15.2)	8.8 (6.9–11.2)	10.7 (8.6–13.3)
Alcohol use						<.001
None	7.2 (6.2–8.3)	7.1 (5.2–9.5)	6.6 (5.2–8.5)	6.8 (5.0–9.3)	8.2 (6.3–10.5)
Moderate	33.3 (31.2–35.4)	28.1 (24.3–32.3)	32.1 (28.1–36.4)	36.3 (32.2–40.8)	36.3 (32.3–40.5)
Heavy	42.9 (40.8–45.0)	47.6 (43.5–51.8)	46.5 (42.3–50.7)	40.9 (36.7–45.2)	37.2 (33.3–41.3)
Not recorded	16.6 (15.3–18.1)	17.2 (14.5–20.3)	14.8 (12.5–17.4)	15.9 (13.3–19.0)	18.4 (15.5–21.7)
BMI						<.001
<25	26.5 (24.6–28.4)	23.1 (19.8–26.8)	21.9 (18.6–25.7)	24.6 (21.1–28.6)	35.5 (31.6–39.6)
25–30	30.9 (29.0–32.9)	20.3 (17.2–23.7)	30.3 (26.6–34.2)	39.0 (34.8–43.4)	33.8 (29.9–37.8)
≥30	41.8 (39.7–43.9)	55.5 (51.3–59.5)	47.1 (43.0–51.4)	35.8 (31.8–39.9)	29.9 (26.3–33.8)
Not recorded	0.8 (0.6–1.1)	1.2 (0.7–2.0)	0.7 (0.4–1.3)	0.6 (0.3–1.2)	0.9 (0.4–1.6)
Physical activity						<.001
Inactive	46.9 (44.8–49.0)	45.5 (41.4–49.6)	44.4 (40.3–48.6)	43.7 (39.5–48.0)	53.5 (49.3–57.6)
Less active	8.6 (7.4–9.9)	6.2 (4.6–8.3)	9.4 (7.1–12.5)	9.5 (7.2–12.5)	9.3 (7.1–12.0)
Active	44.1 (42.0–46.3)	48.1 (43.9–52.2)	45.8 (41.6–50.0)	46.4 (42.1–50.7)	36.7 (32.8–40.8)
Not recorded	0.4 (0.2–0.8)	0.3 (0.2–0.6)	0.4 (0.2–0.7)	0.4 (0.2–0.9)	0.5 (0.1–3.0)
Aspirin Use						<.001
Yes	19.0 (17.4–20.7)	17.8 (14.8–21.2)	13.9 (11.3–17.0)	18.8 (15.7–22.4)	24.9 (21.4–28.7)
Smoking status						<.001
Nonsmoker	58.5 (56.4–60.6)	46.5 (42.3–50.7)	59.0 (54.7–63.2)	61.7 (57.4–65.8)	66.7 (62.6–70.5)
Former smoker	24.6 (22.8–26.6)	25.9 (22.3–29.9)	24.6 (20.8–28.8)	24.2 (20.6–28.1)	23.8 (20.4–27.6)
Current smoker	16.8 (15.4–18.4)	27.7 (24.4–31.2)	16.4 (13.7–19.5)	14.1 (11.4–17.3)	9.5 (7.3–12.4)
CKD						<.001
Yes	15.0 (13.7–16.4)	17.1 (14.5–20.0)	16.5 (13.9–19.5)	10.2 (8.3–12.5)	16.6 (13.8–19.8)
Albuminuria						.002
Yes	10.0 (9.0–11.2)	11.4 (9.3–13.9)	11.1 (9.2–13.4)	7.4 (5.8–9.3)	10.3 (8.0–13.0)
Low eGFR						.003
Yes	7.1 (6.2–8.1)	8.2 (6.4–10.3)	7.9 (6.0–10.3)	4.8 (3.5–6.6)	7.5 (5.8–9.6)

Values are weighted mean ± standard deviation or weighted % (95% confidence interval). P-values are weighted.

UACR: urinary albumin to creatinine ratio; SCr: serum creatinine; eGFR: estimated glomerular filtration rate; hs-CRP: high-sensitivity C-reactive protein; BUN: blood urea nitrogen; SUA: serum uric acid; Hb: hemoglobin; TC: total cholesterol; HDL: high-density lipoprotein; LDL-C: low-density lipoprotein cholesterolemia; VC: vitamin C; BMI: body mass index; CKD: chronic kidney disease.

Table 2. Associations between serum vitamin C level and CKD (n = 4969).

	CKD (Yes, n = 958)	Model 1 OR (95%CI) p	Model 2 OR (95%CI) p	Model 3 OR (95%CI) p
Quartiles of vitamin C, umol/ L
Q1(< 30.4)	274	Reference	Reference	Reference
Q2(30.4–50.3)	240	0.96 (0.72, 1.27) .777	0.97 (0.71, 1.32) .843	0.99 (0.71, 1.40) .983
Q3(50.3–67.6)	168	0.55 (0.41, 0.74) <.001	0.51 (0.37, 0.71) <.001	0.53 (0.37, 0.77) .001
Q4(≥ 67.6)	276	0.96 (0.72, 1.29) .806	0.72 (0.52, 0.99) .048	0.75 (0.51, 1.09) .128
P trend	–	<.001	<.001	<.001
Sensitivity analysis after exclusion of participants with dietary vitamin C supplement (None, n = 3301)
Quartiles of vitamin C, umol/ L N = 595
Q1(< 30.4)	247	Reference	Reference	Reference
Q2(30.4–50.3)	174	0.97 (0.71, 1.35) .886	1.05 (0.74, 1.50) .776	1.01 (0.69, 1.48) .971
Q3(50.3–67.6)	90	0.47 (0.33, 0.68) <.001	0.48 (0.33, 0.71) <.001	0.45 (0.29, 0.71) .001
Q4(≥ 67.6)	84	0.67 (0.44, 1.06) .086	0.65 (0.40, 1.04) .073	0.59 (0.37, 0.96) .032
P trend	–	<.001	<.001	<.001

Model 1: unadjusted model; Model 2: minimally adjusted model, adjusted for: gender, age, race; Model 3: fully adjusted model, adjusted for: gender, age, race, hs-CRP, diabetes, hypertension, education, alcohol use, physical activity, aspirin use, smoking, dietary vitamin C intake by food, vitamin C supplement, poverty income ratio, BMI.

CKD: chronic kidney disease; OR: odds ratio; 95% CI: 95% confidence interval.

Table 3. Associations between serum vitamin C level and albuminuria (n = 4969).

	Albuminuria (Yes, n = 681)	Model 1 OR (95%CI) p	Model 2 OR (95%CI) p	Model 3 OR (95%CI) p
Quartiles of vitamin C, umol/ L
Q1(< 30.4)	196	Reference	Reference	Reference
Q2(30.4–50.3)	173	0.97 (0.71, 1.33) .847	0.92 (0.67, 1.27) .626	0.97 (0.68, 1.37) .858
Q3(50.3–67.6)	129	0.62 (0.44, 0.87) .005	0.59 (0.42, 0.83) .003	0.63 (0.43, 0.93) .021
Q4(≥ 67.6)	183	0.89 (0.62, 1.26) .505	0.76 (0.52, 1.12) .161	0.78 (0.51, 1.20) .252
p trend	–	<.001	<.001	<.001
Sensitivity analysis after exclusion of participants with dietary vitamin C supplement (None, n = 3301)
Quartiles of vitamin C, umol/ L N = 436
Q1(< 30.4)	177	Reference	Reference	Reference
Q2(30.4–50.3)	118	0.92 (0.65, 1.30) 0.630	0.87 (0.62, 1.24) .439	0.85 (0.57, 1.27) .432
Q3(50.3–67.6)	71	0.55 (0.36, 0.83) .005	0.53 (0.35, 0.82) .004	0.54 (0.33, 0.88) .014
Q4(≥ 67.6)	70	0.81 (0.49, 1.36) .432	0.77 (0.46, 1.30) .327	0.76 (0.45, 1.27) .289
p trend	–	<.001	<.001	<.001

Model 1: unadjusted model; Model 2: minimally adjusted model, adjusted for: gender, age, race; Model 3: fully adjusted model, adjusted for: gender, age, race, hs-CRP, diabetes, hypertension, education, alcohol use, physical activity, aspirin use, smoking, dietary vitamin C intake by food, vitamin C supplement, poverty income ratio, BMI.

OR: odds ratio; 95% CI: 95% confidence interval.

Table 4. Associations between serum vitamin C level and low eGFR (n = 4969).

	Low eGFR (Yes, n = 446)	Model 1 OR (95%CI) p	Model 2 OR (95%CI) p	Model 3 OR (95%CI) p
Quartiles of vitamin C, umol/ L
Q1(< 30.4)	130	Reference	Reference	Reference
Q2(30.4–50.3)	114	0.96 (0.65, 1.43) .853	1.06 (0.67, 1.69) .792	1.03 (0.61, 1.73) .911
Q3(50.3–67.6)	78	0.57 (0.37, 0.87) .009	0.52 (0.32, 0.82) .005	0.53 (0.32, 0.88) .015
Q4(≥ 67.6)	124	0.91 (0.62, 1.33) .616	0.56 (0.37, 0.84) .006	0.56 (0.33, 0.94) .029
p trend	–	<.001	<.001	<.001
Sensitivity analysis after exclusion of participants with dietary vitamin C supplement (None, n = 3301)
Quartiles of vitamin C, umol/ L N = 263
Q1(<30.4)	119	Reference	Reference	Reference
Q2(30.4–50.3)	85	0.99 (0.62,1.58) .979	1.31 (0.75,2.28) .342	1.39 (0.79,2.44) .250
Q3(50.3–67.6)	34	0.39 (0.23,0.64) <.001	0.41 (0.24,0.72) .002	0.43 (0.23,0.81) .010
Q4(≥67.6)	25	0.42 (0.22,0.78) .006	0.40 (0.20,0.78) .007	0.39 (0.19,0.84) .015
p trend	–	<.001	<.001	<.001

Model 1: unadjusted model; Model 2: minimally adjusted model, adjusted for: gender, age, race; Model 3: fully adjusted model, adjusted for: gender, age, race, hs-CRP, diabetes, hypertension, education, alcohol use, physical activity, aspirin use, smoking, dietary vitamin C intake by food, vitamin C supplement, poverty income ratio, BMI.

eGFR: estimated glomerular filtration rate; OR: odds ratio; 95% CI: 95% confidence interval.

Data availability statement

Publicly available datasets were analyzed in this study. These data can be found here: https://www.cdc.gov/nchs/nhanes/.