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Respiratory Diseases in Children

5. Can indoor air pollution contribute to respiratory diseases in children?

  • 5.1 In what way can children be exposed to and affected by indoor pollution?
    • 5.1.1 Pollution sources
    • 5.1.2 Respiratory health effects
  • 5.2 What air pollutants can affect children at home?
    • 5.2.1 Cigarette smoke
    • 5.2.2 Damp housing with mould growth, mite infestation, cockroaches and toxins
    • 5.2.3 Presence of pets and other animals
    • 5.2.4 Use of polluting fuels for cooking and heating
    • 5.2.5 Indoor chemicals from building materials, paintings, carpets and furniture
  • 5.3 What air pollutants can affect children at school and in their spare time?

The source document for this Digest states:

European children spend more time in indoor than outdoor environments so much so that more than 90% of their waking hours are spent indoors and the burden for many chemical substances with health consequences is much higher than outdoors. The effects of indoor air pollution are of special interest in relation to respiratory health and allergic disorders including asthma. Here the main concern centers around the question as to what extent different exposures give rise to different effects and to what extent these effects in turn translate to health risks. Allergic diseases are, therefore, included in the following report where they are relevant to respiratory health. The coexistence of allergic disease for example in children with asthma is associated with an increased risk of persistence into adult life. [Wolfe et al 2000].

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the
European Environment and Health Strategy (COM(2003)338 final), (2003)
Section 8 Indoor Exposure/Indoor Environmental Risk Factors

5.1 In what way can children be exposed to and affected by indoor pollution?

    • 5.1.1 Pollution sources
    • 5.1.2 Respiratory health effects

The source document for this Digest states:

Depending on the age of the children, the effects of different air pollution exposure conditions can differ widely. As far as indoor exposures are concerned, 3 different environments can be distinguished: 1) the home environment, 2) the child’s outside-the- home environment (day care, Kindergarten, school), 3) environment of recreational activities (swimming pools, etc.)

The pollution burden of these different environments, where a child’s daily activities take place, can vary considerably. We have to assume, however, and this has been confirmed in environmental epidemiological studies, that exposure in the home- environment is very important considering the time spent in this environment. Exposure where ‘recreational activities’ take place are specific to that environment and may be recognised as ‘hot spots’ where the exposure burden exceeds the recommended limits.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the
European Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.1

5.1.1 Pollution sources

The source document for this Digest states:

Indoor air pollutants can be classified into chemical, biological or physical agents. It should, however, be pointed out that these may occur as mixtures, be present as a background or may arise simultaneously. Sources of indoor pollution are outdoor emission sources, permanent indoor sources or intermittent indoor sources (e.g., mainly due to human activities or lifestyle habits). Background indoor sources include hazardous building materials and contamination of indoor furnishings, such as furniture and carpets. Intermittent sources are due to human activities and habits, such as smoking, cooking, home renovations or the use of cleaning agents disinfectants or air-fresheners. In addition, the continuous stress on energy-saving policies in environmental politics leads to the situation that less and less air exchange occurs in our homes and office buildings. Thus, to the above mentioned source-dependent pollutants mites, moulds and bacteria may be added. These problems not only arise in the ‘cold’ climates of Central and Northern Europe, but due to the increased use of air conditioners also in the warmer climatic zones of Southern Europe.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European
Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.1

5.1.2 Respiratory health effects

The source document for this Digest states:

Respiratory illnesses can be acute and short lived or chronic and persistent. Important indoor-pollution-associated diseases include infections of the upper and lower respiratory tract, and non-obstructive pulmonary diseases (simple chronic bronchitis), irritation of the airways and with respect to allergic disease manifestations rhino conjunctivitis and exacerbations of asthma. Particular indoor-pollution-associated symptoms which may occur include wheezing, cough and bronchial hypersecretion. Current data do not allow a detailed comparison overview in Europe. The reason lies not only in the fact that specific studies in important areas are missing but Europe is plagued with the habit of still not using uniform diagnostic criteria. Although there appears to be a gradient for symptomatic asthma from north west to south east Europe (see section 1) there is considerable overlap in the expression of the disease and for hay fever in the main European regions (Table) [ISAAC, 1998].

Figure 6 : Expression of the disease and for hay fever in the main European regions

Europe-wide, only a few studies have been concerned with the effects of complex indoor pollution on the respiratory system of children, despite the fact that the dose resulting from a stay indoors generally is above the outdoors-related dose. Examples of these types of studies are:

- ASMA Asthma study [Liard et al., 2002]

- BAMSE Barn Allergi Miljö i Stockholm- en Epidemiologisk undersökning (Children Allergy Environment in Stockholm- an Epidemiological survey [Wickmann et al., 2002]

- ECA Environment and Childhood Asthma [Lodrup Carlsen, 2002]

- KIGA Kindergarten Children Study on Allergies and Airway Diseases [Herbarth et al., 2001, 1998]

- LARS Allergy Risk Children Study [Diez et al., 2003; Herbarth et al., 1999]

- LISA Lifestyle-ImmuneSystem-Allergy Study [Lehmann et al., 2001]

- MAS Multicentre Allergy Study [Lau et al., 2002]

- PIAMA Prevention and Incidence of Asthma and Mite Allergy [Brunekreef et al., 2002]

A summary presentation of studies can be found under AIRNET:
(http://airnet.iras.uu.nl/inventory/index.php )

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the
European Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.1

5.2 What air pollutants can affect children at home?

    • 5.2.1 Cigarette smoke
    • 5.2.2 Damp housing with mould growth, mite infestation, cockroaches and toxins
    • 5.2.3 Presence of pets and other animals
    • 5.2.4 Use of polluting fuels for cooking and heating
    • 5.2.5 Indoor chemicals from building materials, paintings, carpets and furniture

5.2.1 Cigarette smoke

The source document for this Digest states:

Passive smoking or environmental tobacco smoking (ETS) is the indoor pollution variable that has been most intensively studied. Not only does smoking in the presence of a child have an effect on the manifestation of respiratory symptoms but also has an adverse effect on the developing fetus of mothers who smoke. [Burr 1999, Burr et al., 1999]. Exposure to cigarette smoke in utero and in the immediate post natal period is also a major risk factor for sudden infant death syndrome (SIDS) (see below). During childhood, wheezing is the most pronounced symptom [Diez et al., 2000, OIE et al., 1999, Zacharasiewicz 1999]. ETS, particularly in utero, leads to a decrease in pulmonary function, increased asthmatic symptoms and an increase in bronchial hyper responsiveness [Lodrup Carlsen 2002, Lodrup Carlsen et al., 2001, Bogacka 2002, Liard et al., 2002]. Whereas postnatal or environmental tobacco smoke (ETS) exposure has a significant influence or respiratory morbidity in the young [Taylor & Wadsworth 1987] the effects of prenatal exposure are likely to be more long lasting. Studies which have assessed lung function soon after birth, when the effects of ETS would be expected to be small have shown evidence of reduced airway function [Hanrahan et al 1992, Young et al 1991]. Whereas it is clearly not possible to identify the exact mechanisms of these effects in humans, animal studies have shown that fetal ETS significantly reduces cell division in the lung as evidenced by reduced DNA, alveolar number and connective tissue within the lung [Collins et al1985, Vidic et al 1989].

A recent systematic review demonstrated a consistent relationship between parents’ smoking and respiratory illnesses and symptoms and middle ear disease in children with odds ratios between 1.2 and 1.6 [Cook & Strachan, 1999]. The odds are greater for preschool children and higher for maternal compared with paternal smoking. The latter observation might be explained by increased exposure to maternal rather than paternal smoking among preschool children. Alternatively, a prenatal effect of maternal smoking on the developing fetal lungs might be responsible. One of the difficulties of disentangling the interrelationships of prenatal and postnatal tobacco smoke exposure on children’s respiratory symptoms in epidemiological studies is the observation that prenatal maternal smoking is almost always associated with postnatal tobacco smoke exposure. However whatever the mechanism it is clear that environmental tobacco smoke exposure (ETS) is an important and potentially remediable cause of respiratory morbidity in the young.

Several studies have demonstrated an association between prenatal tobacco smoke exposure and decrements in pulmonary function in infants soon after delivery and before the onset of symptoms. Such decrements appear to be associated with respiratory symptoms during the first year after birth [Martinez et al, 1988; Stick et al, 1996; Dezateux et al, 1999] and it seems likely that in utero smoke exposure causes growth restraint of fetal airways. The longer term effects of such fetal growth restraint have yet to be determined. Recent studies have attempted to examine the differential effects of intrauterine and postnatal tobacco smoke exposure on the outcomes of asthma and wheezing in later childhood. Gilliland and colleagues (2001) have demonstrated associations between in utero exposure and physician diagnosed asthma in later childhood but, although current or past environmental (postnatal) exposure was related to wheezing symptoms, there was not a significant relationship with asthma. The authors speculated that environmental exposure may act as a cofactor for attacks of wheezing but did not appear to be a factor that induced asthma in this population.

Parental smoking has also been demonstrated in several case control and cohort studies [Mitchell, 1995] to be significantly associated with sudden infant death syndrome (SIDS). Maternal smoking was associated with increased risk and a dose response effect has been demonstrated in several studies, suggesting a casual relationship, and, although smoking rates vary with socio-economic status, the risk appears to be consistent across socio-economic groups. Fleming and colleagues (1996) in a study of sudden infant death after the ‘Back to Sleep’ campaign in the United Kingdom calculated an odds ratio of SIDS for maternal smoking during pregnancy of 2.1 with an additional independent effect of paternal smoking. The mechanisms for this effect has not been elucidated but fetal lung growth restraint or effects of smoking on neurological responses to thermal, hypoxic or hypercapnic stress have been postulated. ETS also contributes to exacerbation of allergic symptoms [Baier et al., 2002, Diez et al., 2000]. Pre- and post natal ETS exposure increases a child’s sensitisation to food allergens [Kulig et al., 1999, 1999] and changes in the nasal mucous membrane have been observed in genetically predisposed children [Vinke et al., 1999].

Many studies have concentrated on the respiratory health effects of passive exposure to tobacco smoke in children. However, active smoking by children remains a significant health problem. A recent survey of 14-16 year old children revealed that 30% had been active smokers in the previous 12 months, with 14.1% reporting regular smoking [Withers et al, 2000].

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.2.1

5.2.2 Damp housing with mould growth, mite infestation, cockroaches and toxins

The source document for this Digest states:

Due to the ever increasing energy-saving standards, the air exchange between indoor and outdoor air is really limited. The consequence is a build-up of humidity indoors. This promotes the growth of micro-organisms as well as their associated allergens and toxins. The most important role play mites and moulds and occasionally bacterial- and mould-secreted toxins. Indoor allergens are associated with atopic disorders [Timonen et al., 2002] and an increase in adverse respiratory health effects with mites and moulds being the most important [Muller et al., 2002, Burr 2001, Savilahti et al., 2000, Meklin et al., 2002, Jedrychowski et al., 1997, Zureik et al., 2002]. Furthermore, an increase in wheezing, asthma and bronchial hyperresponsiveness [Lau et al., 2000, Zacharasiewicz 1999, 2000] as well as indoor-allergen-associated changes in lung function [Langley et al., 2003] were being observed. Endo- as well as mycotoxins affect allergic and non- allergic airway diseases, whereby endotoxins are assumed to may have a protective effect on the development o allergic sensitisation [Gereda et al., 2002]. An effect of mycotoxins on the immune-competent cells, on the other hand, could experimentally be demonstrated [Wichmann et al., 2002], which allows to conclude that a direct effect on atopic disorders is possible. As far as the lifetime age range for these exposures is concerned, it appears that exposures in the first 3 years have the greatest effect. With increased likelyhood of flooding consequent upon intense periods of rainfall in association with climate change, exposure of children to the conditions of damp housing may increase in the coming years.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European
Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.2.1

5.2.3 Presence of pets and other animals

The source document for this Digest states:

The keeping of pets and other animals is being discussed controversially in the literature. On the one hand, findings suggest that pets/animals are associated with an increase in sensitisation towards allergens but, on the other hand, allergy-protective effects have been reported [for an overview see de Blay et al., 2003]. Part of this observed protective effect may be due to avoidance strategies by the parents whose children suffer from hay fever or are already sensitised [Anyo 2002]. Other authors report on marginal effects of animal allergens or no effect at all [Foucard et al., 2000]. Nevertheless, animals with a proven effect on sensitisation rates are pets such as cats and dogs [Langley et al., 2003, Reijonen et al., 2000]. Reijonen and colleagues report especially the effect on dermatitis and asthma. This current controversy may in part be explained by the timing of exposure to animals. Exposure in utero and/or in infancy may result in tolerance to associated animal allergens whereas later exposure to sensitisation and expression of allergic symptoms.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European
Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.2.1

5.2.4 Use of polluting fuels for cooking and heating

The source document for this Digest states:

Cooking and heating, particularly, with gas has been found to affect respiratory illnesses in children. Responsible are obviously the NOx. Observed effects were an increase in respiratory diseases [Burr 1999] and respiratory infections, an increase in the susceptibility to asthma [de Marco, 2001] and the occurrence of bronchial asthma and allergic disease [Bogacka, 2002] as well as changes in lung function [Corbo et al., 2001].

It can be assumed that especially the extensive use of cleaning agents may influence the respiratory health of children. Studies about it do not exist. There are some indications that these substances (occupational environment) may affect the respiratory system of adults.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European
Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.2.1

5.2.5 Indoor chemicals from building materials, paintings, carpets and furniture

The source document for this Digest states:

Indoor chemicals are found in any indoor environment. High concentrations occur especially following renovation activities or renewal of the furnishings. Exposure to these chemicals affect airway diseases, in particular, wheezing, respiratory symptoms and asthma, as well as allergic disorders in children [Diez et al., 2003, 2000; Herbarth et al., 2003; Clarisse et al., 2002; Jaakola et al., 2000; de Blay et al., 1999]. Important here is early exposure, possibly even exposure during pregnancy [Herbarth et al., 2003]. Critical is that parents, more often than not, carry out these home renovation activities just in time when they are expecting a baby and that just before birth. The effects of volatile organic compounds (VOC) on the immune sysem could experimentally be determined, which may in part explain these health effects [Lehmann et al., 2002a, 2002b, 2001]. It could also be shown that exposure to indoor chemicals during early childhood increases the risk to microbiological-dependent airway diseases [Diez et al., 2000]. This appears related to irritations of the nasal and respiratory tract mucosa, which besides VOC and SVOC may be due to the effects of among others phthalate plasticisers and flame retardants [Kimmel et al., 2000]. Aldehydes and glycol- compounds are also suspected to adversely affect the respiratory system.

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European Environment and Health Strategy (COM(2003)338 final), (2003) Section 8.2.1

5.3 What air pollutants can affect children at school and in their spare time?

The source document for this Digest states:

Day care and preschool children

The influence of the non-domestic indoor environment on the respiratory health of infants and young children in day care and Kindergartens has not been extensively investigated, but it is likely that the same factors as those described for the home environment will operate. Consequently, efforts should be directed at controlling or reducing exposure to environmental tobacco smoke, allergens (including moulds), gases originating from cooking and heating appliances, and VOCs from cleaning agents, disinfectants, building materials and outdoor (traffic) air pollution.

School children

Similar considerations apply to children of school age. With increasing age, appropriate preventive efforts should be conducted to prevent and delay the initiation of tobacco smoking. This should include a total ban on smoking in school premises, including by teachers and staff. The detrimental effects of cannabis smoking on the respiratory tract should not be ignored. In adolescents, a special attention should be devoted to pupils following vocational or technical education. Practical classes and on-the-job training may involve hazardous exposures (e.g. welding, woodworking, food industry, animal handling) for which appropriate legislative, technical and educational provisions should be available. The teaching of preventive attitudes in these pupils is likely to be of critical importance for their future careers. Occupational asthma has been shown to occur already in students and apprentices in at risk jobs (bakers, hair dressers, spray painters, animal technicians).

Competent school health services should be available to provide appropriate counseling for choosing a particular type of education and future job that is compatible with the child’s health state (atopy, asthma, cystic fibrosis).

Recreation and sports

It is well known that physical exercise during play and sports results in a higher exposure of the airways and lungs to higher amounts of pollutants, such as ozone, than at rest. It is, therefore, of importance that sports can take place in areas with the cleanest possible environment. The practice of sports in cold areas has been shown to affect asthma. During recreation, children may also spend time indoors in youth clubs, sports halls, and swimming pools, etc. Recent studies have indicated that the release of chloramines in the air of chlorinated swimming pools may represent a significant hazard for respiratory health [Bernard et al. 2003].

Source & ©: EU   "Baseline Report on Respiratory Health" in the framework of the European Environment and Health Strategy (COM(2003)338 final), (2003)" Section 8.2 Exposure


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