Interventions to reduce individual exposure of elderly individuals and children to haze: a review

Introduction

Rapid economic development and urbanisation in China over the last few decades has led to the increased occurrence of hazy weather in some regions (1,2). In December 2013, a hazardous large-scale haze covered China and affected 25 provinces and over 100 cities. According to information from China Meteorological Administration, in 2013, the average number of haze weather days in the eastern area of China was 36, which is 27 days more than those previously tallied during the same period every year since 1961. Recent studies demonstrate that haze pollution and outdoor air pollutants are associated with increased hospital admissions and mortality risk in Guangzhou, China (3,4). According to the Global Burden of Disease Study (5), a staggering 3.2 million people died from air pollution in 2010, 2.1 million of whom were from Asia. Haze is now a worldwide phenomenon that has gained attention because of its adverse effects on public health.

Air pollutants in haze

Haze is an atmospheric phenomenon characterised by visibility of less than 10 km. Haze is created by complex materials, such as dust, smoke and other fine particles that are suspended in air. The main components of haze are particulate matter (PM) and gaseous pollutants (6). Studies on the health effects of haze have mainly focused on PM2.5, which is defined as fine PM with an aerodynamic diameter of less than 2.5 µm. PM2.5 is the main health hazard among the components of haze because it can penetrate deep into the lungs. A study found that the proportion of PM2.5 was three times larger than that of coarse PM in distal pulmonary tissues (7). PM1 is a subset of inhalable PM2.5 particles that can eventually spread into the systemic circulation through the alveolar-capillary membrane. PM1 can trigger inflammation of blood vessels, the heart and other organs. Air pollution in China is mainly caused by fossil fuels, motor vehicles, industrial dust, furnaces, stoves and agricultural practices (e.g., controlled burns) (8).

Health effects of haze

A good understanding of how air pollution affects human health is essential to the advocacy of developing intervention measures geared towards improving air quality and prevention strategies to reduce subsequent impacts on human health. Specific populations, particularly children and older adults, are potentially more susceptible than the general population to PM-induced effects. Children and older adults are more susceptible PM-induced effects because of physiological differences (9). Children are more susceptible than adults to the effects of PM because of the greater amount of time spent outdoors, activity levels and minute volume per unit body weight of this subpopulation that lead to increases in PM dose per lung surface area and, in turn, increases in the susceptibility of developing lungs to adverse effects. The elderly are generally considered a susceptible population because of the gradual decline in physiological processes over time. Compared with children or younger adults, elderly individuals have a higher prevalence of pre-existing cardiovascular and respiratory diseases, which may also confer susceptibility to PM.

Environmental epidemiology research conducted in recent decades has proven that short-term or long-term exposure to ambient PM increases mortality and morbidity, reduces life expectancy and increases the risk of respiratory and cardiovascular diseases (10-12). Studies on asthmatic children have reported that increases in respiratory symptoms, increased medication use and decreases in pulmonary function are associated with short-term PM2.5 exposure (13-15). A case-crossover study in Taipei found that chronic obstructive pulmonary disease (COPD) admissions are significantly and positively associated with higher PM2.5 levels during warm and cool days (16). Moreover, large amounts of toxic compounds, such as gases, organic compounds and heavy metals, adhere to the surface of PM2.5, resulting in increased toxicity, interference with chromosomes, DNA and other genetic material. PM2.5 and toxic compounds are also implicated in the development of cancers. Long-term fine particulate air pollution exposure is associated with small but measurable increase in lung cancer mortality (17,18).

Consistent evidence from epidemiological studies demonstrates that short- and long-term exposure to PM, specifically PM2.5, is associated with cardiovascular morbidity and mortality (19). PM concentration is also linked to myocardial infarction (20), heart failure (21) and arrhythmia (22). The elderly, diabetics and those with known coronary artery disease appear specifically susceptible to the harmful effects triggered by PM exposure. Long-term exposure to fine particulate air pollution is also an important risk factor influencing cardiovascular disease mortality via mechanisms that include pulmonary and systemic inflammation, accelerated atherosclerosis and altered cardiac autonomic function (23).

Ultrafine particles of even smaller size can easily reach the brain from the respiratory tract via sensory neurons and travel from the distal alveoli into the blood or lymph as free particles. A study found that increases in PM2.5 concentration are associated with increased risks of emergency hospital admissions for cerebrovascular diseases (24). Motor, cognitive and behavioural changes are observed after particulate metal exposure in children (25). Children may be at particular risk from air pollution exposure because childhood and adolescence are crucial periods of brain development associated with dynamic behavioural, cognitive and emotional changes.

Besides particles, other air pollutants, such as ambient ozone, carbon monoxide, sulphur oxides, nitrogen oxides and lead also have hazardous effects on human health. Ozone is a powerful oxidant and respiratory tract irritant in adults and children. Increases in ambient ozone are associated with increased respiratory admissions among young children and the elderly (26) and reduced lung function in children (27). A study found that short-term exposure to Black Carbon (BC) presents a positive monotonic dose—response relationship with acute respiratory inflammation in school children living in Beijing (28). This relationship was not confounded by PM2.5, which is not as strongly associated with eNO. Lead is neurotoxic, especially during early childhood. A study found that blood lead levels are more sensitive to changes in air lead concentrations among children and older adults compared with teenagers and adults (29).

Interventions

National and regional air pollution policies and regulations are important to reduce air pollution and decrease hazy days. The Chinese Government has committed to spend 3.4 trillion on environmental protection in the 12^th Five Year Plan. The air pollution prevention action plan, published in September 2013, calls for strict controls on pollution, industry production and coal consumption, implementation of clean production processes and promotion of clean vehicles. Although the Chinese public and government have paid increased attention to air pollution, changing the current situation entails a long process of improvement. Individual protection to reduce air pollution exposure is also necessary. In this study, we introduce interventions to reduce the exposure of elderly and children to pollutants during hazy weather.

Outdoor interventions

In developed countries, motor vehicles are a major source of air pollution. The pollution created by motor vehicles has substantial impacts on ambient air pollution and personal exposures. Traffic-related emissions include large amounts of reactive gases and ultrafine particles. Very high local concentrations of reactive gases, ultrafine particles and other combustion products are observed on or near major highways and roadways. People who live close to major roads are expected to be exposed to higher concentrations of traffic-related air pollutants and have higher risks of adverse health effects. During hazy weather, traffic-related air pollutants may be more difficult to diffuse. Therefore, outdoor interventions are very important during hazy weather.

Avoid outdoor activities

Motor vehicles are the major source of air pollution in many communities. Motor vehicles pollute the air through tailpipe exhaust emissions and fuel evaporation, which contribute to carbon monoxide, PM2.5, nitrogen oxides, hydrocarbons, other hazardous air pollutants and ozone formation. The concentration of traffic pollutants is greater near major roads than in minor ones. A large and growing number of studies have reported that children living near traffic or high levels of ozone, nitrogen dioxide or PM have increased risks of adverse respiratory effects (30-33). Other studies report that increased risks of cardiac and respiratory adverse effects are associated with air traffic-related pollution inhalation in elderly individuals (34,35). Therefore, the public, especially children and the elderly, should avoid outdoor activities when the air quality index is in the unhealthy range. Susceptible individuals should avoid walking or riding on a bicycle along streets when traffic is heavy.

Wear facemasks

Studies conducted in China confirm that the use of face masks in extremely polluted cities could reduce exposure and result in lower inflammatory and cardiovascular responses. A study showed that wearing a facemask appears to abrogate the adverse effects of air pollution on blood pressure and heart rate variability in healthy volunteers (36). Another study also found that face masks are a simple and practical intervention to reduce an individual’s exposure to particulate air pollution. The use of facemasks improves several cardiovascular health measures in individuals with coronary heart disease (37). Different types of masks are available in the market. Knowing which type of mask is suitable for haze is essential. The mask penetrance of fresh diesel exhaust particulates is highly dependent on the mask type. In two studies, the 3M Dust Respirator (Model 8812, 3M, St Pauls, USA) was selected for an intervention study because it provided good filtration performance and was extremely efficient and comfortable to wear. The 3M Dust Respirator mask is made of a light-weight polypropylene filter that is effective in removing airborne PM without affecting ambient gases. The mask has an expiration valve and an assigned protection factor of four. Several respirator types are specially designed for children. However, wearing masks for extended periods of time may elicit feelings of breathlessness, especially in elderly individuals and people with cardiovascular diseases.

Indoor interventions

The health effects of exposure to air pollution are mainly related to outdoor levels, monitored or modelled in areas around residences. Unfortunately, most people, especially the elderly spend over 80% to 90% of their day indoors (38). The amount of traffic-related particles transported into the indoor environment by ventilation and infiltration is highly variable. Moreover, a large proportion of indoor particulates comes from a variety of indoor sources (e.g., frying, heating devices, environmental tobacco smoke and human activity) and may account for the majority of total personal exposure. A study found that household air pollution is a major avoidable risk factor for cardiorespiratory disease (39). Higher indoor PM concentrations are linked to respiratory symptoms and lower lung functions in children with asthma (40). Therefore, indoor intervention is also important.

Burn fuel more cleanly

Nearly half of the world population burns biomass fuels (e.g., wood, charcoal, dung or crop residues), coal and kerosene (paraffin) as energy sources for household cooking, heating and lighting (41). Burning of biomass fuels, coal and kerosene is a form of energy usage associated with high levels of indoor air pollution and increases in the incidence of acute lower respiratory infections, COPD, lung cancer, asthma, low birth weight, other adverse birth outcomes (42-46), headache (47), neurodevelopment impairments (48), cardiovascular condition (49) and eye diseases, such as cataracts and blindness (50,51). A woodstove change out program conducted in a Rocky Mountain valley community significantly reduced indoor PM2.5 concentrations (52). Although many Chinese families now use coal gas or natural gas for cooking, traditional stoves are still used for cooking in rural China. Burning fuel more cleanly, having a separate kitchen, using kitchen ventilators or electronic fans when cooking and reducing frying can eliminate smoke and reduce indoor air pollution exposure.

Forbid smoking at home

Scientific evidence clearly shows that second-hand smoke exposure causes diseases in adults and children. Children are more vulnerable than adults to the health effects of second-hand smoke; these effects include acute respiratory infection, asthma, sudden infant death syndrome and slow lung growth (53,54). Although many public places have banned indoor smoking in China, in-home smokers have not taken effective precautions to limit the impact of smoking on the home environment. Children’s exposure is involuntary and occurs primarily through adults who smoke in places where children live and play. Despite the known health risks of second-hand smoke to very young children at home, parents have yet to take precautions for protecting their children. Public health messages have not effectively led to changes in smoking behaviours in the home. A study conducted in America reported that the mortality risk brought about by ambient PM exposure is greater for smokers than non-smokers (23). Therefore, the higher prevalence of cigarette smoking amongst Chinese males may increase their mortality risk relative to air pollution exposure. As such, forbidding smoking at home, especially in areas experiencing haze where outdoor air pollution is severe, is necessary to preserve the health of family members.

Promote air filtration

Substantial reductions in exposure to particles can be achieved by portable air filtration units placed in the indoor environment. In a study conducted on elderly people, an 8% improvement in microvascular function (MVF) was detected 48 hours after air filtration was initiated in participant homes (55). A recent review concluded that residential air filtration can improve outcomes in the treatment of allergic respiratory diseases (56). Another study indicated that indoor air filtration may not be sufficient to reduce indoor PM levels to values approaching outdoor concentrations when indoor smoking is present. Therefore, the most obvious and cost-effective means of reducing indoor PM2.5, before considering indoor air filtration, is elimination of indoor cigarette smoking (57).

Outdoor PM concentrations are higher than indoor levels during hazy weather. Therefore, windows should be kept close to prevent outdoor PM from entering. Sweeping shows a significantly positive relationship with indoor PM concentrations, in contrast to vacuuming (58). However, the use vacuum cleaners has not been shown to improve children’s asthma (59). Parents may opt to use a vacuum cleaner rather than sweep when cleaning the house but must remember that cleaning activities should ideally be performed when asthmatic children are not present in the room.

Accept dietary supplementation

Among the plausible biological mechanisms explaining PM2.5 health effects, oxidative stress is often cited to have an important function in both respiratory and cardiovascular outcomes. A diet rich in antioxidants appears to reduce the oxidative and inflammatory effects of air pollution. A study in Mexico City, Mexico, reported that children with asthma who were given antioxidant supplements were less affected by ozone compared with children who did not receive supplementation (60). Another study showed that fish oil supplements, which provide n-3 polyunsaturated fatty acids (n-3 PUFA), could be considered as a preventive measure to reduce risks of arrhythmia and sudden death in elderly individuals exposed to ambient air pollution (61). Air pollution exposure has been linked to neuroinflammation and neuropathology in young urbanites. A study suggested that a short high flavonol cocoa intervention may be critical for early implementation of neuroprotection of highly PM exposed urban children (62).

Conclusions

Given rapid economic developments over the past last few decades, China has experienced frequent haze episodes, which have adverse effects on public health. Our study focused on the use of individual protection by children and the elderly during hazy weather because these subpopulations are more susceptible than the general population to air pollution. In conclusion, outdoor activities must be generally avoided when air quality indices are in the unhealthy range. When going outdoors is unavoidable, wearing a suitable dust mask suitable is necessary. If possible, walking and riding a bicycle must be avoided to minimize exposure to air pollutants. As children and the elderly spend most of their time indoors, indoor air quality must also be monitored during haze episodes. Reducing the burning of biomass fuels, avoiding frying and smoking at home and using an air filtration unit may substantially reduce particle exposure. Antioxidant supplements, fish oil and flavonol-rich dark cocoa, may reduce some of the harmful effects of air pollution. However, the actual benefits of these measures remain unproven. Similarly, the proposal of pharmacological prophylaxis during high PM periods appears premature, and benefits, if any, are unlikely to be adequate. Given the large number of people exposed to haze, the overall air pollution-related health burden is rather extensive. As such, sustained clean-air policies are the most important and efficient solution to reduce air pollution-related health effects.

Acknowledgements

We thank prof. Ian Adcock for his kind revision on this review.

Funding: This work was supported by National Natural Science Foundation of China (Grant 81470237), the Jiangsu Health Promotion Project, and the Priority Academic Program Development of Jiangsu Higher Education Institutions (Grant JX10231802).

Footnote

Conflicts of Interest: The authors have no conflicts of interest to declare.

References

1. Xu P, Chen Y, Ye X. Haze, air pollution, and health in China. Lancet 2013;382:2067. [PubMed]
2. Wang H, Tan SC, Wang Y, et al. A multisource observation study of the severe prolonged regional haze episode over Eastern China in January 2013. Atmos Environ 2014;89:807-15.
3. Zhang Z, Wang J, Chen L, et al. Impact of haze and air pollution-related hazards on hospital admissions in Guangzhou, China. Environ Sci Pollut Res Int 2014;21:4236-44. [PubMed]
4. Liu T, Zhang YH, Xu YJ, et al. The effects of dust-haze on mortality are modified by seasons and individual characteristics in Guangzhou, China. Environ Pollut 2014;187:116-23. [PubMed]
5. Lim SS, Vos T, Flaxman AD, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012;380:2224-60. [PubMed]
6. Zhuang X, Wang Y, He H, et al. Haze insights and mitigation in China: an overview. J Environ Sci (China) 2014;26:2-12. [PubMed]
7. Venkataraman C, Kao AS. Comparison of particle lung doses from the fine and coarse fractions of urban PM-10 aerosols. Inhal Toxicol 1999;11:151-69. [PubMed]
8. Zhang Q, Streets DG, Carmichael GR, et al. Asian emissions in 2006 for the NASA INTEX-B mission. Atmos Chem Phys 2009;9:5131-53.
9. Sacks JD, Stanek LW, Luben TJ, et al. Particulate matter-induced health effects: who is susceptible? Environ Health Perspect 2011;119:446-54. [PubMed]
10. Brunekreef B, Holgate ST. Air pollution and health. Lancet 2002;360:1233-42. [PubMed]
11. Shang Y, Sun Z, Cao J, et al. Systematic review of Chinese studies of short-term exposure to air pollution and daily mortality. Environ Int 2013;54:100-11. [PubMed]
12. Dockery DW, Pope CA 3rd, Xu X, et al. An association between air pollution and mortality in six U.S. cities. N Engl J Med 1993;329:1753-9. [PubMed]
13. Gent JF, Triche EW, Holford TR, et al. Association of low-level ozone and fine particles with respiratory symptoms in children with asthma. JAMA 2003;290:1859-67. [PubMed]
14. Rabinovitch N, Strand M, Gelfand EW. Particulate levels are associated with early asthma worsening in children with persistent disease. Am J Respir Crit Care Med 2006;173:1098-105. [PubMed]
15. Gold DR, Damokosh AI, Pope CA 3rd, et al. Particulate and ozone pollutant effects on the respiratory function of children in southwest Mexico City. Epidemiology 1999;10:8-16. [PubMed]
16. Tsai SS, Chang CC, Yang CY. Fine particulate air pollution and hospital admissions for chronic obstructive pulmonary disease: a case-crossover study in Taipei. Int J Environ Res Public Health 2013;10:6015-26. [PubMed]
17. Turner MC, Krewski D, Pope CA 3rd, et al. Long-term ambient fine particulate matter air pollution and lung cancer in a large cohort of never-smokers. Am J Respir Crit Care Med 2011;184:1374-81. [PubMed]
18. Pope CA 3rd, Burnett RT, Thun MJ, et al. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. JAMA 2002;287:1132-41. [PubMed]
19. Dockery DW. Epidemiologic evidence of cardiovascular effects of particulate air pollution. Environ Health Perspect 2001;109 Suppl 4:483-6. [PubMed]
20. Mustafic H, Jabre P, Caussin C, et al. Main air pollutants and myocardial infarction: a systematic review and meta-analysis. JAMA 2012;307:713-21. [PubMed]
21. Shah AS, Langrish JP, Nair H, et al. Global association of air pollution and heart failure: a systematic review and meta-analysis. Lancet 2013;382:1039-48. [PubMed]
22. Peters A, Liu E, Verrier RL, et al. Air pollution and incidence of cardiac arrhythmia. Epidemiology 2000;11:11-7. [PubMed]
23. Pope CA 3rd, Burnett RT, Thurston GD, et al. Cardiovascular mortality and long-term exposure to particulate air pollution: epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004;109:71-7. [PubMed]
24. Leiva G MA, Santibañez DA, Ibarra E S, et al. A five-year study of particulate matter (PM2.5) and cerebrovascular diseases. Environ Pollut 2013;181:1-6. [PubMed]
25. Lucchini RG, Dorman DC, Elder A, et al. Neurological impacts from inhalation of pollutants and the nose-brain connection. Neurotoxicology 2012;33:838-41. [PubMed]
26. Yang Q, Chen Y, Shi Y, et al. Association between ozone and respiratory admissions among children and the elderly in Vancouver, Canada. Inhal Toxicol 2003;15:1297-308. [PubMed]
27. Kinney PL, Thurston GD, Raizenne M. The effects of ambient ozone on lung function in children: a reanalysis of six summer camp studies. Environ Health Perspect 1996;104:170-4. [PubMed]
28. Lin W, Huang W, Zhu T, et al. Acute respiratory inflammation in children and black carbon in ambient air before and during the 2008 Beijing Olympics. Environ Health Perspect 2011;119:1507-12. [PubMed]
29. Meng Q, Richmond-Bryant J, Davis JA, et al. Contribution of particle-size-fractionated airborne lead to blood lead during the National Health and Nutrition Examination Survey, 1999-2008. Environ Sci Technol 2014;48:1263-70. [PubMed]
30. Morgenstern V, Zutavern A, Cyrys J, et al. Respiratory health and individual estimated exposure to traffic-related air pollutants in a cohort of young children. Occup Environ Med 2007;64:8-16. [PubMed]
31. Brunekreef B, Janssen NA, de Hartog J, et al. Air pollution from truck traffic and lung function in children living near motorways. Epidemiology 1997;8:298-303. [PubMed]
32. Brauer M, Hoek G, Smit HA, et al. Air pollution and development of asthma, allergy and infections in a birth cohort. Eur Respir J 2007;29:879-88. [PubMed]
33. Wjst M, Reitmeir P, Dold S, et al. Road traffic and adverse effects on respiratory health in children. BMJ 1993;307:596-600. [PubMed]
34. Adar SD, Gold DR, Coull BA, et al. Focused exposures to airborne traffic particles and heart rate variability in the elderly. Epidemiology 2007;18:95-103. [PubMed]
35. Hoek G, Brunekreef B, Goldbohm S, et al. Association between mortality and indicators of traffic-related air pollution in the Netherlands: a cohort study. Lancet 2002;360:1203-9. [PubMed]
36. Langrish JP, Mills NL, Chan JK, et al. Beneficial cardiovascular effects of reducing exposure to particulate air pollution with a simple facemask. Part Fibre Toxicol 2009;6:8. [PubMed]
37. Langrish JP, Li X, Wang S, et al. Reducing personal exposure to particulate air pollution improves cardiovascular health in patients with coronary heart disease. Environ Health Perspect 2012;120:367-72. [PubMed]
38. Simoni M, Jaakkola MS, Carrozzi L, et al. Indoor air pollution and respiratory health in the elderly. Eur Respir J Suppl 2003;40:15s-20s. [PubMed]
39. Mortimer K, Gordon SB, Jindal SK, et al. Household air pollution is a major avoidable risk factor for cardiorespiratory disease. Chest 2012;142:1308-15. [PubMed]
40. Koenig JQ, Mar TF, Allen RW, et al. Pulmonary effects of indoor- and outdoor-generated particles in children with asthma. Environ Health Perspect 2005;113:499-503. [PubMed]
41. Rehfuess E, Mehta S, Prüss-Ustün A. Assessing household solid fuel use: multiple implications for the Millennium Development Goals. Environ Health Perspect 2006;114:373-8. [PubMed]
42. Po JY, FitzGerald JM, Carlsten C. Respiratory disease associated with solid biomass fuel exposure in rural women and children: systematic review and meta-analysis. Thorax 2011;66:232-9. [PubMed]
43. Wong GW, Brunekreef B, Ellwood P, et al. Cooking fuels and prevalence of asthma: a global analysis of phase three of the International Study of Asthma and Allergies in Childhood (ISAAC). Lancet Respir Med 2013;1:386-94. [PubMed]
44. Kurmi OP, Arya PH, Lam KB, et al. Lung cancer risk and solid fuel smoke exposure: a systematic review and meta-analysis. Eur Respir J 2012;40:1228-37. [PubMed]
45. Siddiqui AR, Gold EB, Yang X, et al. Prenatal exposure to wood fuel smoke and low birth weight. Environ Health Perspect 2008;116:543-9. [PubMed]
46. Tielsch JM, Katz J, Thulasiraj RD, et al. Exposure to indoor biomass fuel and tobacco smoke and risk of adverse reproductive outcomes, mortality, respiratory morbidity and growth among newborn infants in south India. Int J Epidemiol 2009;38:1351-63. [PubMed]
47. Díaz E, Smith-Sivertsen T, Pope D, et al. Eye discomfort, headache and back pain among Mayan Guatemalan women taking part in a randomised stove intervention trial. J Epidemiol Community Health 2007;61:74-9. [PubMed]
48. Dix-Cooper L, Eskenazi B, Romero C, et al. Neurodevelopmental performance among school age children in rural Guatemala is associated with prenatal and postnatal exposure to carbon monoxide, a marker for exposure to woodsmoke. Neurotoxicology 2012;33:246-54. [PubMed]
49. Baumgartner J, Schauer JJ, Ezzati M, et al. Indoor air pollution and blood pressure in adult women living in rural China. Environ Health Perspect. 2011;119:1390-5. [PubMed]
50. Saha A, Kulkarni PK, Shah A, et al. Ocular morbidity and fuel use: an experience from India. Occup Environ Med 2005;62:66-9. [PubMed]
51. Smith KR, Mehta S. The burden of disease from indoor air pollution in developing countries: comparison of estimates. Int J Hyg Environ Health 2003;206:279-89. [PubMed]
52. Ward T, Palmer C, Bergauff M, et al. Results of a residential indoor PM2.5 sampling program before and after a woodstove changeout. Indoor Air 2008;18:408-15. [PubMed]
53. Jones LL, Hashim A, McKeever T, et al. Parental and household smoking and the increased risk of bronchitis, bronchiolitis and other lower respiratory infections in infancy: systematic review and meta-analysis. Respir Res 2011;12:5. [PubMed]
54. Miller RL, Garfinkel R, Horton M, et al. Polycyclic aromatic hydrocarbons, environmental tobacco smoke, and respiratory symptoms in an inner-city birth cohort. Chest 2004;126:1071-8. [PubMed]
55. Bräuner EV, Forchhammer L, Møller P, et al. Indoor particles affect vascular function in the aged: an air filtration-based intervention study. Am J Respir Crit Care Med 2008;177:419-25. [PubMed]
56. Sublett JL. Effectiveness of air filters and air cleaners in allergic respiratory diseases: a review of the recent literature. Curr Allergy Asthma Rep 2011;11:395-402. [PubMed]
57. Weichenthal S, Mallach G, Kulka R, et al. A randomized double-blind crossover study of indoor air filtration and acute changes in cardiorespiratory health in a First Nations community. Indoor Air 2013;23:175-84. [PubMed]
58. McCormack MC, Breysse PN, Hansel NN, et al. Common household activities are associated with elevated particulate matter concentrations in bedrooms of inner-city Baltimore pre-school children. Environ Res 2008;106:148-55. [PubMed]
59. Custovic A, Wijk RG. The effectiveness of measures to change the indoor environment in the treatment of allergic rhinitis and asthma: ARIA update (in collaboration with GA(2)LEN). Allergy 2005;60:1112-5. [PubMed]
60. Romieu I, Sienra-Monge JJ, Ramírez-Aguilar M, et al. Antioxidant supplementation and lung functions among children with asthma exposed to high levels of air pollutants. Am J Respir Crit Care Med 2002;166:703-9. [PubMed]
61. Romieu I, Téllez-Rojo MM, Lazo M, et al. Omega-3 fatty acid prevents heart rate variability reductions associated with particulate matter. Am J Respir Crit Care Med 2005;172:1534-40. [PubMed]
62. Calderón-Garcidueñas L, Mora-Tiscareño A, Franco-Lira M, et al. Flavonol-rich dark cocoa significantly decreases plasma endothelin-1 and improves cognition in urban children. Front Pharmacol 2013;4:104. [PubMed]