Table 3.
Hazard ratios for incident diabetes per 6.7 ppb O3 stratified by covariatesa.
| Cases/PYs | HRa (95% CI) | |
|---|---|---|
| Neighborhood SES | ||
| Quintile 1 lowest | 1081/85,569 | 1.07 (0.64, 1.78) |
| Quintile 2 | 934/86,213 | 0.80 (0.55, 1.15) |
| Quintile 3 | 879/88,921 | 1.29 (0.96, 1.74) |
| Quintile 4 | 833/95,834 | 1.20 (0.90, 1.60) |
| Quintile 5 highest | 660/96,683 | 1.69 (1.21, 2.36) |
| Interaction p-value | 0.27 | |
| BMI | ||
| <25 | 298/135,021 | 1.11 (0.64, 1.93) |
| 25–29 | 1184/154,702 | 1.08 (0.83, 1.40) |
| ≥30 | 2905/163,498 | 1.26 (1.08, 1.48) |
| Interaction p-value | 0.98 | |
| Age | ||
| <40 | 655/133,509 | 1.27 (0.93, 1.72) |
| 40–54 | 2200/224,159 | 1.21 (1.02, 1.44) |
| ≥55 | 1532/95,553 | 1.16 (0.93, 1.44) |
| Interaction p-value | 0.34 | |
| Education | ||
| ≤HS | 980/71,966 | 1.06 (0.77, 1.48) |
| Some college | 1476/142,585 | 1.13 (0.89, 1.43) |
| College graduate | 1926/238,024 | 1.19 (0.98, 1.44) |
| Interaction p-value | 0.65 | |
| Parental history of diabetes | ||
| Yes | 2072/135,222 | 1.14 (0.93, 1.40) |
| No | 2236/310,344 | 1.17 (0.99, 1.40) |
| Interaction p-value | 0.71 | |
| Presence of hypertension | ||
| No | 1932/310,669 | 1.10 (0.90, 1.33) |
| Yes | 2455/142,551 | 1.22 (1.02, 1.46) |
| Interaction p-value | 0.55 | |
| Vigorous exercise | ||
| <5 h/week | 4157/407,886 | 1.18 (1.03, 1.35) |
| ≥5 h/week | 187/41,596 | 1.37 (0.69, 2.70) |
| Interaction p-value | 0.66 | |
| Smoking | ||
| Never | 2344/281,409 | 1.13 (0.95, 1.36) |
| Past or current | 2037/170,892 | 1.18 (0.97, 1.45) |
| Interaction p-value | 0.51 | |
| Meat/fried food diet pattern score | ||
| Quintile 1 | 700/87,221 | 1.19 (0.82, 1.73) |
| Quintile 2 | 755/85,892 | 1.19 (0.85, 1.67) |
| Quintile 3 | 814/86,307 | 1.21 (0.89, 1.65) |
| Quintile 4 | 866/86,104 | 1.22 (0.89, 1.68) |
| Quintile 5 | 965/84,832 | 1.11 (0.80, 1.54) |
| Interaction p-value | 0.95 | |
| Vegetable/fruit diet pattern score | ||
| Quintile 1 | 810/79,953 | 1.39 (0.98, 1.96) |
| Quintile 2 | 835/83,068 | 0.94 (0.67, 1.33) |
| Quintile 3 | 798/86,354 | 1.26 (0.89, 1.79) |
| Quintile 4 | 843/89,243 | 1.21 (0.88, 1.66) |
| Quintile 5 | 814/91,738 | 1.22 (0.91, 1.64) |
| Interaction p-value | 0.87 | |
| Max air temperature | ||
| Tertile 1 | 1456/150,404 | 1.26 (0.91, 1.77) |
| Tertile 2 | 1390/144,718 | 1.22 (0.87, 1.72) |
| Tertile 3 | 1538/157,761 | 1.16 (0.99, 1.36) |
| Interaction p-value | 0.80 | |
| Max heat index | ||
| Tertile 1 | 1429/151,728 | 1.18 (1.01, 1.39) |
| Tertile 2 | 1164/125,095 | 0.95 (0.67, 1.36) |
| Tertile 3 | 1765/173,575 | 1.35 (0.96, 1.88) |
| Interaction p-value | 0.22 | |
We tested effect modification for all variables used as confounders. We also tested for modification with hypertension because there is evidence that hypertension increases the risk for diabetes formation. We hypothesized therefore that individuals with hypertension might be more susceptible to the effects of air pollution. There is also evidence that hypertension is associated with air pollution exposure, and it could be on the causal pathway from air pollution to diabetes. We therefore did not include this disease condition as a confounder, but only as a modifier. We also tested the heat stress variables because of prior evidence that the health effects of ozone may be modified by heat stress.