Background: Ozone has heterogeneous effects on lung function. We investigated whether obesity and airways hyperresponsiveness (AHR) modify the acute effects of ozone on lung function in the elderly.
Methods: We studied 904 elderly men from the Normative Aging Study whose lung function (FVC, FEV1) was measured approximately every 3 years from 1995 to 2005. We defined obesity as a body mass index of at least 30 kg/m2. Using a standardized methacholine challenge test, we defined AHR as a FEV1 decline of 20% after inhalation of a cumulative dosage of 0 to 8.58 μmol of methacholine. Ambient ozone in the Greater Boston area was measured continuously. We estimated effects using mixed linear models, adjusting for known confounders.
Results: An increase in ozone of 15 parts per billion during the previous 48 h was associated with a greater decline in FEV1 in the obese (−2.07%; 95% confidence interval [CI], −3.25 to −0.89%) than in the nonobese (−0.96%; 95% CI, −1.70 to − 0.20%). The same exposure was also associated with a greater decline in FEV1 for those with AHR (−3.07%; 95% CI, −4.75 to −1.36%) compared to those without AHR (−1.32%; 95% CI, −2.06 to −0.57%). A three-way interaction trend test demonstrated a multiplicative effect of those two risk factors (p < 0.001). We found similar associations for FVC.
Conclusions: Our results indicate that both obesity and AHR modify the acute effect of ozone on lung function in the elderly, with evidence of interaction between AHR and obesity that causes a greater than additive effect.