In: Health28 Nov 2014
Interrelationships Between Air Pollution and Other Factors in the Development of Chronic Airways Disease
One pointer in the past to the possible role of air pollution in the development of CAD was the marked urban excess of bronchitis mortality seen in the UK, but this excess has been diminishing for some considerable time (Table 2). Such a trend is consistent with the general decline in air pollution which, especially in London, had been evident to some extent for two or three decades prior to the introduction of the Clean Air Act in 1956. Whether the improvement in terms of mortality might be attributable to reduced exposure in the latter years of life, to the overall reduction in lifetime exposures or perhaps to changes in exposure at a more specific period, such as in childhood, cannot be judged effectively from a simple inspection of mortality data, and urban/rural comparisons are in any case compounded by other factors such as different smoking prevalences or selective migration in and out of cities.
A strong geographic relationship has been shown between chronic bronchitis death rates and infant mortality from bronchitis and pneumonia some 50 years earlier (Fig 1). The authors of this study consider that long-term exposure to air pollution during adult life may be less important in relation to mortality from bronchitis than had previously been supposed. Their findings indicate that childhood respiratory infections (at least in the past) have been an important determinant and that the steep downward trend in bronchitis mortality seen in England and Wales during recent decades is linked with the decline in infant bronchitis and pneumonia earlier this century.
There is also increasing evidence from survey work that events in early life are relevant to the development of CAD, and that air pollution may play a part in the sequence of events. Thus, in the cohort of children born in Great Britain in 1946 who have been followed from birth, it was shown at an early stage that the incidence of lower respiratory tract illnesses in the preschool years was quite strongly related to the general pollution levels of the areas in which they lived (Table 3), and this association persisted throughout the school years. other
Subsequent follow-up during the early adult years showed that smoking soon became the overwhelming factor in the development of respiratory symptoms, but there was still some residual effect of early respiratory illnesses. In the most recent follow-up, at age 36, it was again shown that current cigarette smoking was the main determinant of the prevalence of respiratory symptoms, but other factors, including social conditions now and in the past, and histories of respiratory illness up to age 10, were also relevant. The authors considered that the findings added support for a link between childhood chest illness and subsequent adult chest disease and that reducing exposure to certain environmental influences could contribute to prevention. While the earlier studies on this particular cohort had shown an apparent role of general urban air pollution, the authors commented that currently (in prevailing UK circumstances) indoor air pollution by cigarette smoke is probably the only important factor that can readily be altered.
Table 2—Bronchitis Age Specific Death Rates, Males Aged 60-64, Greater London and Rural Districts of England and Wales
|Year of death||Approx. Year of Birth||Deaths per 100,000|
Table 3—1946 Birth Cohort: Percentage of Subjects Reporting Lower Respiratory Tract Illnesses (Bronchitis, Pneumonia or Bronchopneumonia) by Air Pollution Category
|Illnesses Reported||Air Pollution Category|
|First attack in first 9 mo.||7.2||11.4||16.5||17.1|
|One or more attacks in first 2 yr||19.4||24.2||30.0||34.1|
|Two or more attacks in first 2 yr||4.3||7.9||11.2||12.9|
|Hospital admission in first 5 yr||1.1||2.3||2.6||3.1|
Figure 1. Standardized mortality ratios for chronic bronchitis in men aged 35-74 during 1968-78 and infant mortality from bronchitis and pneumonia per 1,000 births in 1921-5 in 212 areas of England and Wales. X = county boroughs; A = London boroughs; 0 = urban areas; 4- = rural areas. (From Barker and Osmond, by permission.1S)
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