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<h5 class="section-title" id="d3146309e156">Background</h5>
<p id="P2">Chronic health effects of traffic-related air pollution, like nitrogen
dioxide (NO
<sub>2</sub>), are well-documented. Animal models suggested that NO
<sub>2</sub> exposures dysregulate cortisol function.
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<h5 class="section-title" id="d3146309e167">Objectives</h5>
<p id="P3">We evaluated the association between traffic-related NO
<sub>2</sub> exposure and adolescent human cortisol concentrations, utilizing measures
of the
cortisol diurnal slope.
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<h5 class="section-title" id="d3146309e175">Methods</h5>
<p id="P4">140 adolescents provided repeated salivary cortisol samples throughout
one day. We
built a land use regression model to estimate chronic NO
<sub>2</sub> exposures based on home and school addresses. We then generated model-based
estimates
of the association between cortisol and NO
<sub>2</sub> exposure one year prior to cortisol sampling, examining changes in cortisol
diurnal
slope. The final model was adjusted other criteria pollutants, measures of psychosocial
stress, anthropometry, and other demographic and covariates.
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<h5 class="section-title" id="d3146309e186">Results</h5>
<p id="P5">We observed a decrease in diurnal slope in cortisol for adolescents exposed
to the
estimated 75th percentile of ambient NO
<sub>2</sub> (high exposure) relative to those exposed at the 25th percentile (low
exposure).
For a highly exposed adolescent, the log cortisol was lower by 0.06 μg/dl at waking
(95% CI: −0.15, 0.02), 0.07 μg/dl at 30 minutes post waking (95% CI: −0.15, 0.02),
and higher by 0.05 μg/dl at bedtime (95% CI: 0.05, 0.15), compared to a low exposed
adolescent. For an additional interquartile range of exposure, the model-based predicted
diurnal slope significantly decreased by 0.12 (95% CI: −0.23, −0.01).
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<h5 class="section-title" id="d3146309e194">Conclusions</h5>
<p id="P6">In adolescents, we found that increased, chronic exposure to NO
<sub>2</sub> and the mixture of pollutants from traffic sources was associated with
a flattened
diurnal slope of cortisol, a marker of an abnormal cortisol response which we hypothesize
may be a mechanism through which air pollution may affect respiratory function and
asthma in adolescents.
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