Table 1.
Baseline characteristics of the study population according to urinary sodium excretion and 25-hydroxyvitamin D groups
| Characteristics | Total (n=5051) | Low Na+ and Low 25(OH)D (n=1726) | Low Na+ and High 25(OH)D (n=1640) | High Na+ and Low 25(OH)D (n=803) | High Na+ and High 25(OH)D (n=882) | P Value | |
|---|---|---|---|---|---|---|---|
| Urinary sodium excretion, mmol/24 h | <156.8 | <156.8 | ≥156.8 | ≥156.8 | — | ||
| Plasma 25(OH)D, ng/ml | <22.6 | ≥22.6 | <22.6 | ≥22.6 | |||
| Men, n (%) | 2391 (47) | 687 (40) | 589 (36) | 528 (66) | 587 (67) | <0.001 | |
| Age, yr | 48.4±11.7 | 49.3±12.4 | 48.6±11.5 | 46.8±11.1 | 47.6±10.9 | <0.001 | |
| Season, n (%) | — | <0.001 | |||||
| Summer (June–August) | 1069 (21) | 216 (13) | 476 (29) | 95 (12) | 282 (32) | — | |
| Autumn (September–November) | 1555 (31) | 442 (26) | 596 (36) | 179 (22) | 338 (38) | — | |
| Winter (December–February) | 1039 (21) | 481 (28) | 214 (13) | 247 (31) | 97 (11) | — | |
| Spring (March–May) | 1388 (28) | 587 (34) | 354 (22) | 282 (35) | 165 (19) | — | |
| Ethnicity, n (%) | — | — | — | — | — | <0.001 | |
| White | 4810 (96) | 1588 (93) | 1615 (99) | 735 (93) | 872 (99) | — | |
| Black | 45 (1) | 28 (2) | 1 (0.1) | 15 (2) | 1 (0.1) | — | |
| Asian | 100 (2) | 61 (3.6) | 9 (1) | 28 (4) | 2 (0.2) | — | |
| Other | 60 (1) | 31 (2) | 7 (0.4) | 17 (2) | 5 (1) | — | |
| Body mass index, kg/m2 | 25.7±3.9 | 25.4±4.0 | 24.9±3.4 | 27.1±4.6 | 26.5±3.6 | <0.001 | |
| Smoking status, n (%) | — | — | — | — | — | <0.001 | |
| Never | 1597 (32) | 553 (32) | 507 (31) | 266 (33) | 271 (31) | — | |
| Quit >1 yr | 1622 (32) | 501 (29) | 545 (33) | 239 (30) | 337 (38) | — | |
| Quit <1 yr | 197 (4) | 64 (4) | 69 (4) | 28 (4) | 36 (4) | — | |
| Current | 1621 (32) | 599 (35) | 517 (32) | 267 (33) | 238 (27) | — | |
| Type II diabetes, n (%) | 95 (2) | 33 (2) | 27 (2) | 20 (3) | 15 (2) | 0.52 | |
| History of CVD, n (%) | 168 (3) | 72 (4) | 52 (3) | 22 (3) | 22 (3) | 0.08 | |
| Systolic BP, mmHg | 125.8±17.9 | 126.0±19.3 | 123.5±17.7 | 128.4±16.6 | 127.3±16.2 | <0.001 | |
| Diastolic BP, mmHg | 72.8±9.1 | 72.5±9.3 | 72.0±9.0 | 74.1±8.9 | 73.8±8.7 | <0.001 | |
| BP-lowering drugs, n (%) | 583 (12) | 225 (13) | 179 (11) | 93 (12) | 86 (10) | 0.07 | |
| ACEi or ARB, n (%) | 160 (4) | 51 (4) | 45 (3) | 36 (6) | 28 (4) | 0.07 | |
| Lipid-lowering drugs, n (%) | 254 (5) | 85 (5) | 90 (6) | 40 (5) | 39 (4) | 0.70 | |
| Serum glucose, mg/dl | 82.9 [77.5–90.1] | 82.9 [77.5–90.1] | 82.9 [75.7–88.3] | 84.7 [79.3–91.9] | 84.7 [79.3–93.7] | <0.001 | |
| Serum total cholesterol, mg/dl | 215±43 | 214±43 | 215±43 | 217±41 | 217±42 | 0.20 | |
| Serum HDL cholesterol, mg/dl | 52.1±15.4 | 52.6±15.5 | 54.6±15.4 | 48.1±13.9 | 50.3±15.3 | <0.001 | |
| Serum triglycerides, mg/dl | 98.2 [71.7–141.6] | 93.8 [69.0–136.3] | 94.7 [69.9–132.7] | 108.8 [77.9–161.1] | 107.1 [78.8–149.6] | <0.001 | |
| hsCRP, mg/L | 1.08 [0.49–2.55] | 1.08 [0.48–2.59] | 1.08 [0.49–2.45] | 1.11 [0.48–2.77] | 1.07 [0.54–2.37] | 0.88 | |
| Plasma phosphate, mg/dl | 3.11±0.49 | 3.12±0.49 | 3.10±0.49 | 3.14±0.50 | 3.10±0.50 | 0.35 | |
| Plasma calcium, mg/dl | 9.11±0.37 | 9.11±0.36 | 9.12±0.37 | 9.10±0.35 | 9.13±0.39 | 0.56 | |
| Serum albumin, g/dl | 4.11±0.80 | 4.05±0.85 | 4.07±0.78 | 4.15±0.80 | 4.31±0.72 | <0.01 | |
| Plasma 1,25(OH)2D, pg/ml | 60.6±19.6 | 52.7±15.8 | 68.6±19.5 | 52.1±15.9 | 68.8±20.4 | <0.001 | |
| eGFR, ml/min per 1.73 m2 | 97.3±14.6 | 96.9±15.2 | 95.6±14.5 | 100.2±13.8 | 98.3±14.0 | <0.001 | |
| Urine potassium, mmol/24 h | 71.8±21.0 | 65.4±19.2 | 68.0±19.0 | 81.3±21.2 | 82.8±20.5 | <0.001 | |
| Urine calcium, mmol/24 h | 4.0±2.0 | 3.4±1.6 | 3.7±1.6 | 4.8±2.2 | 5.1±2.2 | <0.001 | |
| Urine albumin, mmol/24 h | 8.1 [5.9–12.1] | 8.0 [5.7–11.8] | 7.4 [5.6–11.1] | 9.3 [6.8–14.2] | 8.9 [6.5–12.7] | <0.001 | |
P values for differences between groups were assessed with ANOVA for normally distributed continuous data, the Kruskal–Wallis test for skewed distributed data, and the chi-squared test for nominal data. Baseline continuous data are reported as mean±SD for normally distributed data or median [interquartile range] for skewed data. The units presented in brackets are the interquartile ranges. 25(OH)D, 25-hydroxyvitamin D; CVD, cardiovascular disease; ACEi, angiotensin–converting enzyme inhibitor; ARB, angiotensin receptor blocker; hsCRP, high-sensitivity C-reactive protein; 1,25(OH)2D, 1,25-dihydroxyvitamin D.