Background
Air pollution, particularly from vehicle exhaust, has been shown to influence hormonal activity. However, at present, it is unknown whether air pollution exposure is associated with the occurrence of uterine leiomyomata, a hormonally sensitive tumor of the uterus.
Methods
Proximity to major roadways and outdoor levels of PM less than 10 microns (PM10) or 2.5 microns (PM2.5) or between 10 and 2.5 microns (PM10–2.5) in diameter were determined for all residential addresses from September 1989 to May 2007 for 85,251 women aged 25–42 at enrollment in the Nurses’ Health Study II who were alive and responding to questionnaires, premenopausal with intact uteri, without diagnoses of cancer, or prevalent uterine leiomyomata. Incidence of ultrasound- or hysterectomy-confirmed uterine leiomyomata and covariates were reported on biennial questionnaires sent through May 2007. Multivariable time-varying Cox proportional hazard models were used to estimate the relation between distance to road or PM exposures and uterine leiomyomata risk.
Results
During 837,573 person-years of follow-up, there were 7,760 incident cases. Living close to a major road and exposures to PM10 or PM10–2.5 were not associated with an increased risk of uterine leiomyomata. However, each 10 µg/m3 increase in 2-year average, 4-year average, or cumulative average PM2.5 was associated with an adjusted hazard ratio (HR) of 1.08 (95% confidence interval (CI):1.00–1.17), 1.09 (95%CI:0.99–1.19) and 1.11 (95%CI:1.03–1.19), respectively.
Conclusions
Chronic exposure to PM2.5 may be associated with a modest increased risk of uterine leiomyomata.