Cardiopulmonary Benefits of Reducing Indoor Particles
China has one of the worst air pollution levels in the world, and the government and society are making significant efforts to reduce air pollution levels. Research on easy and effective means of reducing air pollution in China may therefore have substantial public health implications. In this crossover intervention study in Shanghai, China, we found that closing doors and windows barely reduced indoor PM2.5 concentration. In contrast, indoor use of air purifiers efficiently reduced indoor PM2.5 within hours of operation. Furthermore, this improvement in air quality resulted in improved cardiopulmonary function in 35 generally healthy college students. To the best of our knowledge, this is the first study to examine the impact of short-term purification of indoor air on clinical and biochemistry measures of cardiorespiratory health in areas with severe air pollution.
Short-term indoor air purification may have cardiovascular benefits. In the current study, we found a modest but statistically significant decrease in BP after the intervention. This finding is in contrast to those from several previous air filtration studies in countries with cleaner air, which suggests that these cardiovascular benefits may be more easily achieved in regions with severe air pollution problems. Moreover, with indoor air purification, we also observed improvements in nearly all of the 14 examined blood biomarkers of inflammation, coagulation, and vasoconstriction, particularly for proinflammatory proteins such as MCP-1, interleukin-1β, and myeloperoxidase, but not CRP. This nonsignificant effect on CRP is consistent with 2 home-based air filtration studies in Copenhagen, Denmark, but conflicts with another similar study in a wood smoke–impacted community in Canada. In the intervention period, we found a significant decrease in circulating sCD40L, a surface adhesion molecule involved in both inflammatory and thrombogenic processes. A prior air filtration study also reported reduced expression of other adhesion molecules. However, the present study did not demonstrate a significant benefit for the remaining biomarkers, whereas these associations were reported in several observational panel studies. Consistent with another air filtration study among 37 Canadian residents, the nonsignificant effects on the majority of blood biomarkers may be explained by the relatively small sample size, which makes the effect estimates more imprecise.
Our data also suggest beneficial effects of air purification on respiratory health. For example, we found a 17.0% reduction in FeNO, an established biomarker of airway inflammation that can be incipiently induced by the inhalation of PM2.5. The current study show modest, nonsignificant beneficial impacts on lung function, probably because of the short intervention period. Two previous intervention studies, both conducted in areas with lower ambient air pollution, reported conflicting results on indoor air purification and lung function. In a study in Denmark that reduced PM2.5 from 8 to 4 μg/m, there was no significant association of 2 to 14 days of indoor air purification with lung function improvements. In the second study, 7 days of indoor air purification was associated with significantly improved lung function in young adults in Manitoba, Canada.
Taken together, results from this interventional study demonstrated clear, albeit modest, cardiopulmonary benefits of using an indoor air purifier in China. Because our study participants were healthy young adults, one could reasonably expect similar or even larger cardiopulmonary benefits of air purification among vulnerable populations, such as young children or older adults. Furthermore, the potential for additional benefits with a longer intervention can be expected and should be investigated. The use of air purifiers offers ordinary citizens a feasible and affordable way to reduce exposure to hazardous air pollution in a highly polluted developing country, such as China, leading to significant public health benefits.
This study contributes to our understanding about potential biological mechanisms of PM2.5 and health by examining a short-term intervention of reducing PM2.5 exposure and a range of clinical and biochemical markers. Previous human studies have linked short-term PM2.5 exposure to a wide range of adverse cardiopulmonary endpoints; however, most of these were observational panel studies that evaluated changes in health indicators in association with natural day-to-day variations in ambient PM2.5 concentrations. Residual confounding may occur because of a number of individual characteristics and environmental factors, such as weather conditions. Therefore, controlled-exposure interventional studies offer a viable alternative to investigate the causal relationship between ambient PM2.5 and health parameters, but this kind of evidence is largely lacking. Overall, our results supported the biological mechanisms proposed by previous observational studies.
Our study has strengths. First, this randomized, double-blind crossover design facilitated causal inferences of air purification, reduction of air pollutants, and improved health indicators. Second, we measured more indicators of cardiorespiratory health than previous studies, which enabled a more systematic assessment of the potential health benefits of reducing indoor air pollution. Third, the experimental environment was well controlled in that only PM2.5 was probably different between the 2 groups, and exposure measurement error was minimized. Finally, because this intervention study was completed over a 2-week period, we avoided potential temporal confounding caused by seasonal changes and changes in participant behavior.
First, the study included only 35 participants in 10 rooms. We might therefore have missed some potentially important but modest differences attributable to the relatively small sample size. Second, because of the relatively small sample size and examination of multiple health endpoints, our study was considered exploratory in nature. Third, we chose to enroll college students from school dormitories with a short intervention period to better control for potential confounding that might have been difficult to control in other study settings (e.g., indoor cooking, smoking, medication use, and individual health status). However, this study strategy might have limited the generalizability of our study results and might have led us to underestimate or miss some potential health effects (such as lung function) that may be observed with long-term air purification or in more vulnerable populations. Fourth, we did not monitor indoor gaseous air pollutants and were therefore unable to make a direct inference between PM2.5 reduction and the observed health benefits. Because the dormitory rooms were almost identical, except for the intervention, and because air purifiers could not eliminate gaseous pollutants, we believe that this is not a major concern.
Discussion
China has one of the worst air pollution levels in the world, and the government and society are making significant efforts to reduce air pollution levels. Research on easy and effective means of reducing air pollution in China may therefore have substantial public health implications. In this crossover intervention study in Shanghai, China, we found that closing doors and windows barely reduced indoor PM2.5 concentration. In contrast, indoor use of air purifiers efficiently reduced indoor PM2.5 within hours of operation. Furthermore, this improvement in air quality resulted in improved cardiopulmonary function in 35 generally healthy college students. To the best of our knowledge, this is the first study to examine the impact of short-term purification of indoor air on clinical and biochemistry measures of cardiorespiratory health in areas with severe air pollution.
Short-term indoor air purification may have cardiovascular benefits. In the current study, we found a modest but statistically significant decrease in BP after the intervention. This finding is in contrast to those from several previous air filtration studies in countries with cleaner air, which suggests that these cardiovascular benefits may be more easily achieved in regions with severe air pollution problems. Moreover, with indoor air purification, we also observed improvements in nearly all of the 14 examined blood biomarkers of inflammation, coagulation, and vasoconstriction, particularly for proinflammatory proteins such as MCP-1, interleukin-1β, and myeloperoxidase, but not CRP. This nonsignificant effect on CRP is consistent with 2 home-based air filtration studies in Copenhagen, Denmark, but conflicts with another similar study in a wood smoke–impacted community in Canada. In the intervention period, we found a significant decrease in circulating sCD40L, a surface adhesion molecule involved in both inflammatory and thrombogenic processes. A prior air filtration study also reported reduced expression of other adhesion molecules. However, the present study did not demonstrate a significant benefit for the remaining biomarkers, whereas these associations were reported in several observational panel studies. Consistent with another air filtration study among 37 Canadian residents, the nonsignificant effects on the majority of blood biomarkers may be explained by the relatively small sample size, which makes the effect estimates more imprecise.
Our data also suggest beneficial effects of air purification on respiratory health. For example, we found a 17.0% reduction in FeNO, an established biomarker of airway inflammation that can be incipiently induced by the inhalation of PM2.5. The current study show modest, nonsignificant beneficial impacts on lung function, probably because of the short intervention period. Two previous intervention studies, both conducted in areas with lower ambient air pollution, reported conflicting results on indoor air purification and lung function. In a study in Denmark that reduced PM2.5 from 8 to 4 μg/m, there was no significant association of 2 to 14 days of indoor air purification with lung function improvements. In the second study, 7 days of indoor air purification was associated with significantly improved lung function in young adults in Manitoba, Canada.
Taken together, results from this interventional study demonstrated clear, albeit modest, cardiopulmonary benefits of using an indoor air purifier in China. Because our study participants were healthy young adults, one could reasonably expect similar or even larger cardiopulmonary benefits of air purification among vulnerable populations, such as young children or older adults. Furthermore, the potential for additional benefits with a longer intervention can be expected and should be investigated. The use of air purifiers offers ordinary citizens a feasible and affordable way to reduce exposure to hazardous air pollution in a highly polluted developing country, such as China, leading to significant public health benefits.
This study contributes to our understanding about potential biological mechanisms of PM2.5 and health by examining a short-term intervention of reducing PM2.5 exposure and a range of clinical and biochemical markers. Previous human studies have linked short-term PM2.5 exposure to a wide range of adverse cardiopulmonary endpoints; however, most of these were observational panel studies that evaluated changes in health indicators in association with natural day-to-day variations in ambient PM2.5 concentrations. Residual confounding may occur because of a number of individual characteristics and environmental factors, such as weather conditions. Therefore, controlled-exposure interventional studies offer a viable alternative to investigate the causal relationship between ambient PM2.5 and health parameters, but this kind of evidence is largely lacking. Overall, our results supported the biological mechanisms proposed by previous observational studies.
Our study has strengths. First, this randomized, double-blind crossover design facilitated causal inferences of air purification, reduction of air pollutants, and improved health indicators. Second, we measured more indicators of cardiorespiratory health than previous studies, which enabled a more systematic assessment of the potential health benefits of reducing indoor air pollution. Third, the experimental environment was well controlled in that only PM2.5 was probably different between the 2 groups, and exposure measurement error was minimized. Finally, because this intervention study was completed over a 2-week period, we avoided potential temporal confounding caused by seasonal changes and changes in participant behavior.
Study Limitations
First, the study included only 35 participants in 10 rooms. We might therefore have missed some potentially important but modest differences attributable to the relatively small sample size. Second, because of the relatively small sample size and examination of multiple health endpoints, our study was considered exploratory in nature. Third, we chose to enroll college students from school dormitories with a short intervention period to better control for potential confounding that might have been difficult to control in other study settings (e.g., indoor cooking, smoking, medication use, and individual health status). However, this study strategy might have limited the generalizability of our study results and might have led us to underestimate or miss some potential health effects (such as lung function) that may be observed with long-term air purification or in more vulnerable populations. Fourth, we did not monitor indoor gaseous air pollutants and were therefore unable to make a direct inference between PM2.5 reduction and the observed health benefits. Because the dormitory rooms were almost identical, except for the intervention, and because air purifiers could not eliminate gaseous pollutants, we believe that this is not a major concern.
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