Table 1.
Baseline characteristics of the study participants in the entire cohort and according to the quartiles of PM2.5 concentrations.
| Variable | Entire Cohort | The quartile of PM2.5* | |||
|---|---|---|---|---|---|
| Q1 | Q2 | Q3 | Q4 | ||
| PM2.5 concentration (μg/m3) | 77.7±13.2 | 62.3±9.0 | 72.5±0.5 | 78.6±3.7 | 96.2±5.7 |
| Participants, n | 59 456 | 13 791 | 12 976 | 18 265 | 14 424 |
| Age at baseline, y | 48.4±11.3 | 48.7±10.0 | 50.7±12.1 | 46.7±11.3 | 48.2±11.3 |
| Age in 2004, y | 50.0±11.2 | 52.4±9.3 | 51.3±11.9 | 48.1±11.6 | 49.0±11.3 |
| Male | 39.0% | 42.5% | 34.4% | 40.8% | 37.4% |
| High school education and above | 15.4% | 21.2% | 9.7% | 13.6% | 17.3% |
| Medium-high physical activity | 59.0% | 53.4% | 65.1% | 57.5% | 60.9% |
| Smoking status | |||||
| Never | 73.3% | 69.2% | 77.7% | 69.0% | 78.6% |
| Former | 3.2% | 4.2% | 2.0% | 3.9% | 2.3% |
| Current | 23.6% | 26.6% | 20.3% | 27.1% | 19.1% |
| Alcohol drinkers | 18.0% | 23.6% | 19.2% | 14.7% | 15.7% |
| BMI (kg/m2) | |||||
| < 18.5 | 6.1% | 7.3% | 9.1% | 4.8% | 4.0% |
| 18.5-25.0 | 68.0% | 71.1% | 70.9% | 67.3% | 63.2% |
| ≥ 25.0 | 25.9% | 21.7% | 20.1% | 27.9% | 32.8% |
| SBP, mm Hg | 116.9±11.5 | 114.8±11.6 | 116.6±11.5 | 116.6±11.2 | 119.6±11.2 |
| DBP, mm Hg | 73.6±8.0 | 72.8±8.3 | 72.0±8.3 | 73.8±7.7 | 75.7±7.4 |
| Diabetes mellitus | 3.9% | 2.9% | 2.8% | 4.8% | 4.7% |
| Hypercholesterolemia | 3.5% | 5.6% | 1.8% | 2.6% | 4.2% |
| Average temperature, °C | 14.6±3.1 | 15.4±5.7 | 15.6±0.8 | 14.3±1.7 | 13.5±1.3 |
BMI indicates body mass index; DBP, diastolic blood pressure; PM2.5, fine particulate matter; and SBP, systolic blood pressure.
*
Study participants were categorized into 4 groups based on the quartiles of PM2.5 concentrations. Minimum, 37.0 μg/m3; 25th percentile, 71.9 μg/m3; 50th percentile, 73.7 μg/m3; 75th percentile, 82.2 μg/m3; maximum, 109.1 μg/m3. Thus, Q1: <25th percentile; Q2: 25th-50th percentile; Q3: 50th-75th percentile; Q4: >75th percentile.