Trends in Intervention Research for Reducing Health Effects of Particulate Matter

Abstract

Air pollution, especially particulate matter (PM), is one of the major public health risk factors. More than 91% of the global population lives in areas where air pollution exceeds the World Health Organization (WHO) recommended limits. WHO estimated that air pollution is responsible for approximately 4.2 million deaths every year. PM has serious effects on health outcomes (especially in respiratory and cardiovascular diseases and all-cause morbidity). However, there are few intervention studies on the reduction of PM-exposure related health effects. Currently, air purifiers, masks, behavior and other interventions, diet and medications are the recommended interventions for reducing the effect of PM on health; however, scientific evidence for the effects of these interventions are lacking. Here, we review the intervention studies on PM and aim to identify the recent research trends. Using air purifiers significantly lowered the concentration of PM, resulting in a decrease in inflammation and blood pressure. Similarly, wearing a mask showed changes in lung function and blood pressure; however, there was no remarkable changes in the effects on the cardiovascular system. Therefore, intervention studies are limited and more research is needed.

Key messages

① What is known previously?

The effects of PM on health are well known. However, there are few intervention studies on the reduction of PM-exposure related health effects.

② What new information is presented?

Currently, air purifiers, masks, behavior and other interventions, diet, and medications are the recommended interventions for reducing the health effects of PM. Using air purifiers significantly lowered the concentration of PM, resulting in a decrease in inflammation and blood pressure. Similarly, wearing a mask showed changes in lung function and blood pressure; however, there was no significant change in the effects on the cardiovascular system.

③ What are implications?

Intervention studies are limited; therefore, more research is warranted.

Introduction

Particulate matter (PM) refers to particles with various sizes, compositions, and sources. Particles with a diameter of 10 µm or less and 2.5 µm or less are defined as PM₁₀ and PM_2.5, respectively. Inhalation of PM has adverse effects on the human body. Since the International Agency for Research on Cancer designated PM as a Group 1 carcinogen in 2013 [1], the environmental and public health importance of PM has increased. As of 2016, over 91% of the global population lived in areas where the air pollution levels exceeded the limits established by the World Health Organization (WHO), and the number of premature deaths caused by air pollutants, such as PM, was estimated to be 4.2 million [2].

PM can reportedly increase the risk of all-cause mortality, as well as that of respiratory and cardiovascular diseases [3-5]. Recently, PM has also been shown to be associated with neurodegenerative diseases, mental illness, and diabetes. The mechanisms by which PM affects human health include inflammation, generation of active oxygen species, endotoxin effects, and DNA damage [6,7].

Although some studies in the Republic of Korea have investigated the effects of PM on the progression of various diseases, the number of studies on this subject is inadequate compared to that in Western countries and China. In particular, the number of intervention studies to reduce the human health effects caused by PM exposure is insufficient. Measures such as limiting outdoor activities, wearing masks outdoors, and improving indoor air quality through the use of air purifiers are recommended to reduce the health effects of PM. The PM concentration can be reduced by intervention methods; however, their effects on human health remain controversial. In a domestic study in which air purifiers were used for children with asthma, the indoor PM concentration decreased, thereby reducing the peak expiratory flow [8]. In a study by Lim et al. [9] wearing a mask reduced PM exposure as well as the blood pressure among users. Nonetheless, in areas with high PM levels, there is no reliable scientific evidence supporting the efficacy of using air purifiers and wearing masks in preventing the exacerbation of symptoms in patients with asthma [10]. Previous domestic and international studies on intervention effects have mainly focused on air quality rather than on the corresponding health effects. Therefore, in this study, the interventions used for reducing the PM concentrations were examined based on relevant literature to identify the latest research trends in this field.

Results

1. Domestic/international PM and Health Effects

In recent years, active efforts by the Korean government to reduce PM levels have led to a gradual improvement in the annual average PM concentrations; however, the perceived effect on public health remains insufficient. According to a report by the National Institute of Environmental Research, the annual average PM concentration in the Republic of Korea has steadily decreased since 2002 but is still more than twice as high as the level recommended by the WHO (10 µg/m³) or those of other advanced countries (7.4 µg/m³ in the United States and 11.9 µg/m³ in Japan) [11]. In a meta-analysis, the effect of air pollution exposure on the hospitalization and mortality rates of patients with chronic obstructive pulmonary disease (COPD) was investigated [12]. Elevated concentrations of PM₁₀ and PM_2.5 have been shown to increase the hospitalization rate of patients with COPD for respiratory-related issues. Particularly, the hospitalization and mortality rates of patients with COPD increased by 3.1% and 2.5%, respectively, as the PM_2.5 concentration increased by 10 µg/m³ [13]. Moreover, the number of patients with acute lower respiratory tract infections increased by 15% to 32% from week 1 to week 4 when the daily average PM_2.5 concentration increased by 10 µg/m³ [14]. Epidemiological studies have frequently reported a close and direct correlation between PM and cardiovascular diseases. Pope et al. [15] reported that a 10 µg/m³ increase in the short-term PM_2.5 exposure increased the incidence of acute coronary syndrome by 4.5%. This indicates that even short-term changes in PM concentrations can increase the risk of certain diseases. In a meta-analysis, the systolic and diastolic blood pressures of the study subjects were observed to increase by 1.393 and 0.895 mmHg, respectively, when the PM_2.5 concentration increased by 10 µg/m³, demonstrating the positive correlation between PM_2.5 and hypertension [16]. In addition, PM also disrupts the endocrine system, thereby affecting the incidence of metabolic diseases, such as obesity and diabetes [17-19]. A recent study reported that PM_2.5 also affects the incidence of neurological and mental diseases [20]. According to the results of a meta-analysis, long-term exposure of 1.2 million elderly participants aged ≥50 years to PM_2.5 increased the risk of dementia and Alzheimer’s disease by three times (hazard ratio [HR] 3.26) and almost five times (HR 4.82) [20]. In addition, the risk of depression (odds ratio [OR] 1.19) and suicide (OR 1.05) increased when the PM_2.5 concentration increased by 10 µg/m³; however, no correlation was found between the incidence of these diseases and PM₁₀ exposure [21]. PM also affects the risk of premature birth and low birth weight [22].

2. Domestic/international Trends in Intervention Research

1) Research method

The latest research trends and intervention methods used in intervention research related to PM were investigated through a non-systematic review. The MEDLINE, EMBASE, CINAHL, and Cochrane Library databases were searched for studies published from 1989 to 2020. Keywords such as “air pollution”, “particulate matter”, and “trial/intervention” and their combinations were used. If the information obtained using this search strategy was inadequate, a manual search process was employed to collect more information.

2) Research analysis

Two evaluators conducted the evaluation independently, and the agreement was subsequently examined. The selection criteria for the collected articles were the following: (1) studies that analyzed the changes in health indicators according to the short- and long-term exposure to PM; (2) studies written in English or Korean; (3) studies on humans; and (4) studies that compared the acute/chronic health effects of PM exposure before and after the implementation of the intervention methods. Conversely, the exclusion criteria were (1) papers in which research results were not reported and (2) studies that presented no intervention methods. The research targets are presented in the PICO (Patient, Intervention, Comparison, Outcome) format in Table 1.

Table 1. Key questions in literature review.

Category	Detailed content
Patient	Vulnerable population -Patients with respiratory/cardiovascular diseases -The elderly, children, and the poor -Pregnant women -Residents of areas with high PM concentrations -Residents of areas with heavy traffic -Residents of areas close to industrial complexes -Occupational group exposed to high PM levels General population
Intervention	Air purifier Mask Behavioral guidelines Diet and medications
Comparison	PM exposure Before/after applying the intervention methods
Outcome	General symptoms (e.g., itchy eyes, nose, and throat; cough; phlegm; chest tightness; and difficulty in breathing) Emergency room visit (e.g., asthma attack, acute bronchitis, respiratory infection, and arrhythmia) Outpatient visit rate Morbidity Mortality

PM=particulate matter.

(1) Status of individual-based intervention studies

① Air purifier

In the studies on children, the use of air purifiers considerably reduced the PM_2.5 concentration in their homes, increased the peak expiratory flow, and decreased pulmonary inflammation [8,23,24]. In the studies on adults and elderly people, the use of air purifiers reduced the black carbon and PM_2.5 concentrations, decreasing the systolic and diastolic blood pressures of the subjects [25,26].

② Mask

Wearing a mask is recommended to reduce the exposure to air pollution; however, the number of studies on the efficacy of face masks for reducing the health effects of PM is insufficient. A study by Lim et al. [9] confirmed that the short-term use of masks improves lung function and decreases blood pressure. In studies on healthy adults, the group that wore masks exhibited a decreased blood pressure and an increased heart rate variability [27,28]. Wearing a mask also reduced the incidence of depression and the blood pressure and increased the heart rate variability in patients with coronary heart disease [29]. Conversely, wearing a mask while using the subway showed no clear impact on the cardiovascular system of individuals wearing mask [28,30].

③ Individual behavior and other interventions

Not many studies have evaluated the behavioral guidelines related to air pollution. A study involving a group of patients with COPD were educated on COPD self-management behavior demonstrated a decrease in the level of PM exposure and an improvement in some of their symptoms [31]. In addition, pregnant women who received educational text messages regarding air pollution levels, duration, and affected areas demonstrated considerable improvement in their awareness of the risks associated with PM, their preventive behavior, and self-efficacy [32,33]. Regular exercise prevents cardiovascular diseases and low-intensity exercise reduces the burden of cardiopulmonary diseases; however, high-intensity exercise may increase the inhalation of pollutants [34-36]; therefore, the location and corresponding level of air pollution need to be considered beforehand.

④ Diet and medication interventions

Studies focusing on the effectiveness of diet and medications that can minimize the exposure to air pollutants and their adverse health effects are inadequate. A study reported that taking vitamin B for 4 weeks can alleviate the effects of the exposure to high PM concentrations on the cardiac autonomic nervous system functions (heart rate and heart rate variability) and inflammation in adults [37]. Another study reported that taking omega-3 resulted in an improvement in oxidative damage biomarkers in the blood [38].

(2) Status of the national/regional community-based intervention research

National and regional intervention policies have been implemented to reduce the generation of PM to prevent the associated adverse health effects. They include vehicle restrictions, fuel substitution policies for cars and buses, and industrial regulation policies to limit the pollution generated by factories. Policy intervention and regulations of emission sources can effectively reduce the PM concentrations and the associated adverse health effects.

Conclusion

Several international studies have investigated the health effects of PM on individuals who are sensitive and vulnerable to its exposure. In contrast, research on this topic in the Republic of Korea has been relatively limited. Therefore, more comprehensive research is warranted for various populations that are sensitive and vulnerable to PM exposure. Due to limited intervention studies on reducing the health effects of PM in the Republic of Korea and other countries, there is a lack of scientific evidence supporting countermeasures that individuals can implement in their daily lives. Currently, various intervention methods, such as air purifiers, masks, certain behaviors and other interventions, and diet and medications can be used to reduce the effects of PM on human health. However, it is imperative to conduct research on the health effects of the combined application of various intervention methods, as well as the effects of individual intervention methods. In this study, the trends in intervention research to minimize the health effects of PM were examined. The findings of this study will contribute to the development of new intervention methods and the establishment of a foundation for increasing public awareness of the health risks associated with PM.