Table 1.
Baseline characteristics of study participants.
| Characteristics | Overall (n = 22,702) | Tertiles of blue days (days/year) | P value | ||
|---|---|---|---|---|---|
| Worst tertile | Middle tertile | Best tertile | |||
| 3.7–42.0 (n = 7,426) | 42.0–77.4 (n = 6,962) | 77.4–122.3 (n = 8,314) | |||
| Age, years | 56.1 ± 13.1 | 56.2 ± 13.4 | 57.5 ± 12.4 | 54.9 ± 13.3 | <.001 |
| Male | 10,505 (46.3) | 3,512 (47.3) | 2,946 (42.3) | 4,047 (48.7) | <.001 |
| Urban | 10,130 (44.6) | 4,090 (55.1) | 2,530 (36.3) | 3,510 (42.2) | <.001 |
| Han ethnicity | 20,315 (89.5) | 7,360 (99.1) | 5,342 (76.7) | 7,613 (91.6) | <.001 |
| Region | <.001 | ||||
| East | 9,263 (40.8) | 3,167 (42.6) | 2,120 (30.5) | 3,976 (47.8) | |
| Central | 9,460 (41.7) | 4,259 (57.4) | 1,899 (27.3) | 3,302 (39.7) | |
| West | 3,979 (17.5) | 0 (0) | 2,943 (42.2) | 1,036 (12.5) | |
| Education at least middle school | 11,109 (48.9) | 3,783 (50.9) | 3,348 (48.1) | 3,978 (47.8) | <.001 |
| Smoking | <.001 | ||||
| Current | 5,731 (25.2) | 1,878 (25.3) | 1,582 (22.7) | 2,271 (27.3) | |
| Former | 1,216 (5.4) | 313 (4.2) | 450 (6.5) | 453 (5.4) | |
| Never | 15,755 (69.4) | 5,235 (70.5) | 4,930 (70.8) | 5,590 (67.2) | |
| Alcohol consumption | 6,318 (27.8) | 1,893 (25.5) | 1,743 (25.0) | 2,682 (32.3) | <.001 |
| BMI (kg/m2) | <.001 | ||||
| Normal | 10,213 (45.0) | 3,156 (42.5) | 2,994 (43.0) | 4,063 (48.9) | |
| Overweight | 8,533 (37.6) | 2,891 (38.9) | 2,663 (38.3) | 2,979 (35.8) | |
| Obesity | 3,956 (17.4) | 1,379 (18.6) | 1,305 (18.7) | 1,272 (15.3) | |
| Hypertension | 8,957 (39.5) | 2,914 (39.2) | 3,044 (43.7) | 2,999 (36.1) | <.001 |
| Hypercholesterolemia | 7,724 (34.0) | 2,221 (29.9) | 2,488 (35.7) | 3,015 (36.3) | <.001 |
| Diabetes mellitus | 2,286 (10.1) | 706 (9.5) | 840 (12.1) | 740 (8.9) | <.001 |
| Family history of CVD | 2,621 (11.5) | 793 (10.7) | 791 (11.4) | 1,037 (12.5) | <.001 |
| CVD medication history | 4,929 (21.7) | 1,577 (21.2) | 1,892 (27.2) | 1,460 (17.6) | <.001 |
| Ambient temperature, (°C) | 24.6 ± 4.3 | 26.8 ± 2.4 | 22.2 ± 5.7 | 24.7 ± 3.1 | <.001 |
| PM2.5, (μg/m3) | 61.7 ± 22.5 | 70.8 ± 25.2 | 59.0 ± 23.9 | 55.9 ± 15.1 | <.001 |
| NO2, (μg/m3) | 29.3 ± 13.3 | 33.7 ± 11.1 | 26.8 ± 18.4 | 27.4 ± 8.1 | <.001 |
| O3, (μg/m3) | 56.7 ± 10.4 | 56.7 ± 10.7 | 57.1 ± 10.8 | 56.3 ± 9.8 | <.001 |
Numbers are mean ± SD or no. (%). BMI, body mass index; CVD, cardiovascular disease; PM2.5, particles with an aerodynamic diameter of ≤ 2.5 μm; NO2, nitrogen dioxide; O3, ozone.