Ozone Exposure, Outdoor Physical Activity, and Incident Type 2 Diabetes in the SALSA Cohort of Older Mexican Americans

BACKGROUND: Type 2 diabetes is a leading contributor to the global burden of morbidity and mortality. Ozone (O-3) exposure has previously been linked to diabetes. OBJECTIVE: We studied the impact of O-3 exposure on incident diabetes risk in elderly Mexican Americans and investigated whether outdoor physical activity modifies the association. METHODS: We selected 1,090 Mexican American participants from the Sacramento Area Latino Study on Aging conducted from 1998 to 2007. Ambient O-3 exposure levels were modeled with a land-use regression built with saturation monitoring data collected at 49 sites across the Sacramento metropolitan area. Using Cox proportional hazard models, we estimated the risk of developing incident diabetes based on average O-3 exposure modeled for 5-y prior to incident diabetes diagnosis or last follow-up. Further, we estimated outdoor leisure-time physical activity at baseline and investigated whether higher vs. lower levels modified the association between O-3 exposure and diabetes. RESULTS: In total, 186 incident diabetes cases were identified during 10-y follow-up. Higher levels of physical activity were negatively associated with incident diabetes [hazard ratio (HR) = 0.64 (95% CI: 0.43, 0.95)]. The estimated HRs for incident diabetes was 1.13 (95% CI: 1.00, 1.28) per 10ppb increment of 5-y average O-3 exposure; also, this association was stronger among those physically active outdoors [HR = 1.52 (95% CI: 1.21, 1.90)], and close to null for those reporting lower levels of outdoor activity [HR = 1.04 (95% CI: 0.90, 1.20), P-interaction = 0.01]. CONCLUSIONS: Our findings suggest that ambient O-3 exposure contributes to the development of type 2 diabetes, particularly among those with higher levels of leisure-time outdoor physical activity. Policies and strategies are needed to reduce O-3 exposure to guarantee that the health benefits of physical activity are not diminished by higher levels of O-3 pollution in susceptible populations such as older Hispanics.