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Table 1 Characteristics of the study subjects (n = 24,407)

From: Association between exposure to ambient air pollution and renal function in Korean adults

Characteristics Mean ± SD or N (%) Missing
Age (years) 52.8 ± 14.3 0
Female gender 13,933 (57.1) 0
Education level   299
  ≤ Elementary school 7425 (30.8)  
 Middle school 3020 (12.5)  
 High school 7484 (31.0)  
  ≥ College or graduate school 6179 (25.6)  
Smoking   250
 Never 14,012 (58.0)  
 Former-smokers 5023 (20.8)  
 Current-smokers 5122 (21.2)  
Alcohol Consumption (per month)   313
 Never 7382 (30.6)  
  ≤ 1 6659 (27.6)  
 2–3 8108 (33.7)  
  ≥ 4 1945 (8.1)  
Daily protein intake (g) 66.0 (36.3) 2725
Residential region   0
 Urban 15,881 (65.1)  
 Rural 8526 (34.9)  
WC (cm) 82.1 ± 9.6 132
BMI (kg/m2) 23.8 ± 3.2 128
SBP (mm Hg) 120.5 ± 17.8 19
DBP (mm Hg) 77.1 ± 10.7 19
Hypertensiona 8299 (34.0)  
Fasting Glucose (mg/dL) 99.1 ± 24.3 43
Diabetesb 2635 (10.8)  
Total cholesterol (mg/dL) 190.8 ± 36.4 50
Creatinine (mg/dL) 0.9 ± 0.2 0
eGFR mL/min/1.73 m2c 84.4 ± 17.1  
CKDc 1361 (5.6)  
  1. BMI body mass index, WC waist circumference, SBP systolic blood pressure, DBP diastolic blood pressure, eGFR estimated glomerular filtration rate, CKD chronic kidney disease
  2. aHypertension was defined as a systolic blood pressure ≥ 140 mmHg or a diastolic blood pressure ≥ 90 mmHg or taking hypertension treatment medication more than 20 days a month
  3. bDiabetes was defined as fasting glucose ≥126 mg/dL or taking diabetes treatment medication or taking insulin by injection or physician diagnose
  4. ceGFR was calculated by MDRD-4 equation (GFR in mL/min per 1.73 m2 = 175 x SerumCr-1.154 x age-0.203 × 1.212 (if patient is black) × 0.742 (if female))
  5. cCKD was defined as eGFR < 60 mL/min/1.73 m2