Passive smoking or environmental tobacco smoke (ETS) exposure has been variously described as 'second-hand smoke' or 'involuntary smoking'. In the past ...
Original Article
Household Environmental Tobacco Smoke Exposure, Respiratory Symptoms and Asthma in Non-Smoker Adults: A Multicentric Population Study from India D. Gupta1, A.N. Aggarwal1, K. Chaudhry2, S.K. Chhabra3, G.A. D'Souza4, S.K. Jindal1, S.K. Katiyar5, R. Kumar1, B. Shah2 and V.K. Vijayan3 for Asthma Epidemiology Study Group Postgraduate Institute of Medical Education and Research1, Chandigarh; Indian Council of Medical Research2, New Delhi; Vallabhbhai Patel Chest Institute 3, Delhi; St. John's Medical College Hospital 4, Bangalore; and G.S.V.M. Medical College5, Kanpur, India ABSTRACT Background. Exposure to environmental tobacco smoke (ETS ) is a risk factor for childhood asthma. Its association with asthma in adults is less clear. Methods. In a multicentric population study on asthma prevalence in adults, specific enquiries were made into childhood and adulthood exposure to household ETS, and its relationship with asthma diagnosis were analysed. Results. From a total of 73605 respondents, 62109 were studied after excluding current or past smokers. Overall observed prevalence of asthma was 2.0% (men 1.5%,women 2.5%, p 40 hours/week), was significantly associated with development of asthma or hay fever (ORs 1.14-1.22)18. However, a dose response was not conclusively shown. A recent population based case-control study from Finland showed that nearly half of the incident asthma cases were attributable to ETS exposure20. Some case-control studies have failed to demonstrate a convincing association of ETS exposure with asthma in adults. In a study on Swedish farmers, conducted through a postal survey to assess the current and the past ETS exposure, no association of asthma was found with any type of ETS exposure21. The respiratory health impact of passive smoking was studied among 7892 adults (20-48 yrs) who had never smoked in the European Community Respiratory Health Survey22. Compared to “no ETS exposure”, “any ETS exposure” was not associated with a greater risk of self-reported asthma (OR 1.15; 95% CI 0.84-1.58). Another population based study from Singapore also supported the risk of asthma among non smoking adult women residing with heavy smokers (OR 1.6; 95% CI 0.69-3.79)23. One of the factors responsible for conflicting results observed in various studies is the lack of an agreement on, or of a gold standard for, epidemiological definition of asthma. Self reported asthma, the commonly employed tool in most surveys, might underestimate true prevalence24. Several studies therefore report on ‘new onset wheezing’ which is a more sensitive indicator of asthma in adults 25. We also studied the respiratory symptoms in relation to ETS exposure and found significantly higher prevalence of common respiratory symptoms like wheeze, breathlessness and cough among the ETS exposed individuals. Increased prevalence of respiratory symptoms has been reported in several recent studies among nonsmoking adults 26-28. Association of childhood exposure to ETS and asthma in adults has been examined in a population based Swedish study29. The prevalence of asthma was more in adults who were exposed to ETS during childhood, compared to those who were not similarly exposed (7.6% vs 5.8%; p 0.035). Our findings also suggest that childhood exposure is important for
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The Indian Journal of Chest Diseases & Allied Sciences
development of asthma, since exposures only during adulthood were not significantly associated with risk of having asthma in multivariate logistic regression analysis. Exposures from parents or spouse were more deleterious than ETS exposures from other family members, which is logical since the proximity of smoker to the non-smoker individual is an important factor to determine the magnitude of exposure, besides the environmental factors like ventilation, etc. Despite the association of asthma with ETS exposure in both adults and children, the pathogenesis is far less clear. Most of the studies on passive smoking and causation of asthma fulfil only a few of the Hill’s nine criteria for causal association30. Unlike COPD, active smoking is not causally related to asthma. Therefore, the criteria of plausibility, coherence and analogy are not directly applicable. Similarly, the criteria of specificity and experimental evidence also have little relevance. Most studies rely only on the strength of association, consistency, temporality and dose-response relationships. The dose-response relationships have been demonstrated with total daily duration of ETS exposure, number of smokers in the environment, duration of working with a smoker, a cumulative exposure index, or a biomarker of exsposure (nicotine level)18,25. The observation that childhood exposure had higher odds ratios for asthma in adults provides some supporting evidence that ETS exposure (in children) may in fact be causally related the development of bronchial asthma later in life rather than acting as merely a trigger responsible for precipitation of an attack in an established patient. Bronchial hyperresponsiveness (BHR) is central to asthma pathophysiology. The current evidence on effect of ETS on BHR may suggest only a small but real increase in risk and this may be only one of the possible mechanisms involved in causation of asthma due to ETS exposure8,9. Earlier investigators had believed that ETS exposure could lead to allergic sensitization in nonatopic individuals; however the balance of evidence did not support a positive association of atopy with parental smoking either before or after birth 31. We have also demonstrated positive association of ETS exposure with asthma after adjusting for atopy in multivariated analysis. To conclude, household ETS exposure during childhood is a significant risk factor for the development of asthma in adults. Combined ETS exposure from parents during childhood and spouse during adulthood is associated with maximum risk. It is therefore important that the public health campaigns focus at reducing ETS exposures at home as one of the important step towards primary prevention of asthma.
ACKNOWLEDGEMENTS The study was supported by a financial grant from the Indian Council of Medical Research, New Delhi. Authors also express
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their gratitude to members of the Asthma Task Force of Indian Council of Medical Research for their suggestions and help.
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