Ozone exposure and lung function: effect modified by obesity and airways hyperresponsiveness in the VA normative aging study.

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 micromol 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.