Who is more affected by ozone pollution? A systematic review and meta-analysis

Abstract

Ozone is associated with adverse health; however, less is known about vulnerable/sensitive populations, which we refer to as sensitive populations. We systematically reviewed epidemiologic evidence (1988-2013) regarding sensitivity to mortality or hospital admission from short-term ozone exposure. We performed meta-analysis for overall associations by age and sex; assessed publication bias; and qualitatively assessed sensitivity to socioeconomic indicators, race/ethnicity, and air conditioning. The search identified 2,091 unique papers, with 167 meeting inclusion criteria (73 on mortality and 96 on hospitalizations and emergency department visits, including 2 examining both mortality and hospitalizations). The strongest evidence for ozone sensitivity was for age. Per 10-parts per billion increase in daily 8-hour ozone concentration, mortality risk for younger persons, at 0.60% (95% confidence interval (CI): 0.40, 0.80), was statistically lower than that for older persons, at 1.27% (95% CI: 0.76, 1.78). Findings adjusted for publication bias were similar. Limited/suggestive evidence was found for higher associations among women; mortality risks were 0.39% (95% CI: -0.22, 1.00) higher than those for men. We identified strong evidence for higher associations with unemployment or lower occupational status and weak evidence of sensitivity for racial/ethnic minorities and persons with low education, in poverty, or without central air conditioning. Findings show that some populations, especially the elderly, are particularly sensitive to short-term ozone exposure.

Keywords: age; air pollution; effect modifiers; hospitalization; mortality; ozone; sex.

Figure 1.

Percent increase in risk of total mortality for a 10-ppb increase in 8-hour ozone concentration for published studies included in a meta-analysis, by sex, 1988–2013. The open points represent individual study estimates; the closed points and dashed vertical lines represent overall estimates from the meta-analysis. Horizontal lines represent 95% confidence intervals.

Figure 2.

Estimates of the association between ozone exposure and total mortality for published studies included in a meta-analysis, by sex, 1988–2013. Estimates show the percentage increase in risk per 10-ppb increase in 8-hour ozone concentration. The open points represent individual study estimates; the closed points represent “missing studies” for which data were derived from the trim-and-fill method to adjust for publication bias. Solid vertical lines represent overall estimates based on study results; dashed lines represent overall estimates adjusted for publication bias.

Figure 3.

Results from a meta-analysis of associations of ozone exposure with mortality and hospital admission, by sex or age, 1988–2013. A) Risk of mortality by sex; B) risk of mortality by age; C) risk of hospital admission by age. Points represent central estimates for the increase in health risk for a 10-ppb increase in daily 8-hour ozone concentration. Vertical lines represent 95% confidence intervals. CVD, cardiovascular disease.

Figure 4.

Percent increase in risk of total mortality for a 10-ppb increase in 8-hour ozone concentration for published studies included in a meta-analysis, by age, 1988–2013. The open points represent individual study estimates; the closed points and dashed vertical lines represent overall estimates from the meta-analysis. Horizontal lines represent 95% confidence intervals.

Figure 5.

Estimates of the association between ozone exposure and total mortality for published studies included in a meta-analysis, by age, 1988–2013. Estimates show the percentage increase in risk per 10-ppb increase in 8-hour ozone concentration. The open points represent individual study estimates; the closed points represent “missing studies” for which data were derived from the trim-and-fill method to adjust for publication bias. Solid vertical lines represent overall estimates based on study results; dashed lines represent overall estimates adjusted for publication bias.