Breath acidification in adolescent runners exposed to atmospheric pollution: a prospective, repeated measures observational study

Abstract

Background: Vigorous outdoors exercise during an episode of air pollution might cause airway inflammation. The purpose of this study was to examine the effects of vigorous outdoor exercise during peak smog season on breath pH, a biomarker of airway inflammation, in adolescent athletes.

Methods: We measured breath pH both pre- and post-exercise on ten days during peak smog season in 16 high school athletes engaged in daily long-distance running in a downwind suburb of Atlanta. The association of post-exercise breath pH with ambient ozone and particulate matter concentrations was tested with linear regression.

Results: We collected 144 pre-exercise and 146 post-exercise breath samples from 16 runners (mean age 14.9 years, 56% male). Median pre-exercise breath pH was 7.58 (interquartile range: 6.90 to 7.86) and did not change significantly after exercise. We observed no significant association between ambient ozone or particulate matter and post-exercise breath pH. However both pre- and post-exercise breath pH were strikingly low in these athletes when compared to a control sample of 14 relatively sedentary healthy adults and to published values of breath pH in healthy subjects.

Conclusion: Although we did not observe an acute effect of air pollution exposure during exercise on breath pH, breath pH was surprisingly low in this sample of otherwise healthy long-distance runners. We speculate that repetitive vigorous exercise may induce airway acidification.

Figure 1

Distribution of pre- and post-exercise breath pH values in runners. In this group of adolescent runners, there was no significant difference between pre- and post-exercise breath pH (p = 0.63 for nonparametric test of difference in pre- and post-exercise breath pH distributions).

Figure 2

Pre-exercise breath pH by subject (n = 16 subjects, 144 samples), with sprinters denoted by asterisks.

Figure 3

Outdoor resting breath pH was lower in runners (n = 16; green) compared to controls (n = 14; blue). Observed outdoor resting breath pH in this group of adolescent runners was lower than that seen in a control group of non-smoking, healthy adults, none of whom were involved in regular long-distance outdoor running (p = 0.003 by Mann-Whitney U test).