Table 1.
Characteristics of the 4,267 study participants according to season assignment
| Descriptive variables (participants, N) | Spring (N = 1,060) | Summer (N = 979) | Autumn (N = 1,224) | Winter (N = 1,004) | P for trend |
|---|---|---|---|---|---|
| Age, years | 65.6 ± 10.7 | 64.5 ± 11.0 | 65.1 ± 11.3 | 64.2 ± 10.6* | 0.018 |
| Male, % | 45.3 | 45.2 | 47.1 | 50.0 | 0.023 |
| BMI, kg/m2 | 24.4 ± 3.5 | 24.3 ± 3.3 | 24.2 ± 3.6 | 24.3 ± 3.5 | 0.781 |
| Current smoking, % | 11.8 | 11.3 | 13.3 | 12.5 | 0.369 |
| Hypertension, % | 93.2 | 87.6* | 91.8† | 92.7† | 0.559 |
| Use of antihypertensive medication, % | 79.3 | 77.4 | 79.7 | 79.7 | 0.527 |
| Number of classes of antihypertensive medication, N | 1.60 ± 1.18 | 1.52 ± 1.20 | 1.54 ± 1.14 | 1.57 ± 1.17 | 0.862 |
| Diabetes mellitus, % | 23.2 | 25.2 | 25.7 | 23.2 | 0.869 |
| CKD, % | 21.9 | 23.0 | 24.7 | 20.8 | 0.875 |
| Statin treatment, % | 20.5 | 25.6* | 25.0 | 23.5 | 0.126 |
| Pre-existing CVD, % | 10.0 | 14.1* | 13.0 | 13.9* | 0.018 |
| Serum and urine biomarkers | |||||
| Fasting glucose, mg/dl | 107.0 ± 28.6 | 107.3 ± 27.6 | 107.5 ± 27.5 | 108.2 ± 26.6 | 0.025 |
| Total cholesterol, mg/dl | 203.2 ± 32.1 | 199.5 ± 33.2 | 201.8 ± 33.3 | 205.4 ± 33.5† | 0.105 |
| HDL cholesterol, mg/dl | 57.5 ± 15.3 | 55.8 ± 14.7 | 57.6 ± 15.3† | 59.3 ± 15.6* ,†,‡ | <0.001 |
| UACR, mg/g Cr | 13.2 (7.1, 29.1) | 12.3 (6.8, 25.7) | 13.8 (7.4, 35.2) | 13.4 (7.5, 32.8) | |
| Log UACRa | 1.12 (0.85, 1.46) | 1.09 (0.83, 1.41) | 1.14 (0.87, 1.55)† | 1.13 (0.88, 1.52)† | 0.029 |
| BNP, pg/ml | 18.6 (9.0, 36.9) | 19.5 (9.4, 43.2) | 19.3 (9.6, 39.6) | 17.3 (8.9, 34.7) | |
| Log BNPa | 1.27 (0.95, 1.57) | 1.29 (0.97, 1.64)* | 1.29 (0.98, 1.60) | 1.24 (0.95, 1.54)† | 0.301 |
| Office and home BP parameters | |||||
| Office SBP, mm Hg | 142.5 ± 18.0 | 139.4 ± 18.5* | 141.0 ± 18.3 | 141.6 ± 18.5 | 0.757 |
| Office DBP, mm Hg | 81.6 ± 11.3 | 80.8 ± 11.3 | 82.1 ± 11.4 | 82.4 ± 11.6 | 0.020 |
| Morning home SBP, mm Hg | 139.4 ± 15.5 | 134.1 ± 15.6* | 139.3 ± 16.1† | 140.3 ± 15.5† | <0.001 |
| Morning home DBP, mm Hg | 79.2 ± 9.8 | 77.3 ± 10.0* | 79.5 ± 10.2† | 80.3 ± 9.8† | <0.001 |
| Evening home SBP, mm Hg | 131.9 ± 14.9 | 126.7 ± 14.1* | 130.4 ± 15.2† | 131.3 ± 15.2† | 0.551 |
| Evening home DBP, mm Hg | 73.2 ± 9.4 | 71.0 ± 9.4* | 72.9 ± 10.0† | 73.5 ± 9.7† | 0.058 |
Data are expressed as mean ± SD or percentage. UACR and BNP are expressed as median (interquartile range). Pre-existing CVD includes angina pectoris, acute myocardial infarction, and stroke. Statistical significance was assessed using analysis of variance for parametric and categorical data, and Bonferroni correction for multiple comparisons. P values for trend in this table were calculated by Jonckheere–Terpstra’s test for continuous data and Cochran–Armitage trend test for categorical data. Statistical significance was defined as P < 0.05; statistical significant in seasonal differences: *vs. Spring, †vs. summer, and ‡vs. autumn. Abbreviations: BMI, body mass index; BNP, b-type natriuretic peptide; BP, blood pressure; CKD, chronic kidney disease; CVD, cardiovascular disease; DBP, diastolic blood pressure; HDL, high-density lipoprotein; SBP, systolic blood pressure; UACR, urine albumin creatinine ratio.
aMultiple comparisons and P values for trend were calculated in log-transformed UACR and BNP.