Effects of air pollution on restricted activity days: systematic review and meta-analysis

Abstract

Background: The adverse effects of air pollution on human health include many diseases and health conditions associated with mortality, morbidity and disability. One example of these outcomes that can be translated into economic costs is the number of days of restricted activity. The aim of this study was to assess the effect of outdoor exposure to particulate matter with an aerodynamic diameter less than or equal to 10 and 2.5 μm (PM₁₀, PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃), on restricted activity days.

Methods: Observational epidemiological studies with different study designs were included, and pooled relative risks (RR) with 95% confidence intervals (95%CI) were calculated for an increase of 10 μg/m³ of the pollutant of interest. Random-effects models were chosen because of the environmental differences between the studies. Heterogeneity was estimated using prediction intervals (PI) and I-Squared (I2) values, while risk of bias was assessed using a tool developed by the World Health Organization specifically designed for air pollution studies, and based on different domains. Subgroup and sensitivity analyses were performed where possible. The protocol for this review was registered with PROSPERO (CRD42022339607).

Results: We included 18 articles in the quantitative analysis. Associations between pollutants and restricted activity days in time-series studies of short-term exposures, measured as work-loss days, school-loss days, or both were significant for PM₁₀ (RR: 1.0191; 95%CI: 1.0058-1.0326; 80%PI: 0.9979-1.0408; I2: 71%) and PM_2.5 (RR: 1.0166; 95%CI: 1.0050-1.0283; 80%PI: 0.9944-1.0397; I2: 99%), but not for NO₂ or O₃. Some degree of heterogeneity between studies was observed, but sensitivity analysis showed no differences in the direction of the pooled relative risks when studies with a high risk of bias were excluded. Cross-sectional studies also showed significant associations for PM_2.5 and restricted activity days. We could not perform the analysis for long-term exposures because only two studies analysed this type of association.

Conclusion: Restricted activity days and related outcomes were associated with some of the pollutants under evaluation, as shown in studies with different designs. In some cases, we were able to calculate pooled relative risks that can be used for quantitative modelling.

Keywords: Absenteeism; Air pollution; Meta-analysis; Observational study; Systematic review.

Fig. 1

Flowchart of studies selected for inclusion in the meta-analysis

Fig. 2

Percentage of articles with high/low risk of bias in each domain

Fig. 3

Forest plot of 6 time-series studies and one cohort study assessing the association between PM₁₀ and restricted activity days (work-loss days and school-loss days combined). Relative risks for a 10 µg/m³ increase in PM₁₀ level

Fig. 4

Forest plot of 5 time-series studies and one cohort study assessing the association between PM₁₀ and school-loss days. Relative risks for a 10 µg/m³ increase in PM₁₀ level

Fig. 5

Forest plot of four time-series studies, one case-crossover study, and one panel study (8 effect sizes) evaluating the association between PM_2.5 and school-loss days. Relative risks for a 10 µg/m³ increase in PM_2.5 level

Fig. 6

Forest plot of 6 time-series studies and one cohort study evaluating the association between NO₂ and restricted activity days (work-loss days and school-loss days combined). Relative risks for a 10 µg/m³ increase in NO₂ level

Fig. 7

Forest plot of 5 time-series studies and one cohort study evaluating the association between NO₂ and school-loss days. Relative risks for a 10 µg/m³ increase in NO₂ level

Fig. 8

Forest plot of 2 time-series studies, one panel and one cohort study evaluating the association between O₃ and school-loss days. Relative risks for a 10 µg/m³ increase in O₃ level