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9
Introduction

Epidemiologic and experimental studies seek to determine if a relationship exists between a particular exposure and particular health effects. When the exposure is via the air, as is the case with environmental tobacco smoke (ETS) exposure to nonsmokers, the organs that are directly exposed include the eyes, nose, throat, and lungs. Clinical, epidemiologic, and animal studies have shown, generally speaking, that air pollutants can have major health effects on the respiratory system (National Research Council, 1985). Experimental research using animals (Chapter 3) and research with biological markers in humans (Chapter 8) indicate that various constituents of the smoke are absorbed into the blood and, therefore, are transported to organs and tissues of the body. Consequently, the range of possible health effects of exposure to ETS may be very broad and vary enormously in their effect on the individual. Effects may be reversible or irreversible, discomforting, or life-threatening.

In the following chapters, several possible health effects that have received substantial attention are reviewed. Many of the health effects associated with active smoking have been evaluated in studies of nonsmokers exposed to ETS. These include: acute, noxious sensory irritation; nonmalignant respiratory symptoms and disease; decrease in pulmonary function; lung and other cancers; cardiovascular disease; relative growth, ear infections in children; and low birthweight of children of nonsmoking women.

Nonsmokers commonly complain of the perception of tobacco smoke and its irritating, noxious, or annoying qualities. However, in most such spontaneous instances, these complaints are voiced



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Environmental Tobacco Smoke: Measuring Exposures and Assessing Health Effects 9 Introduction Epidemiologic and experimental studies seek to determine if a relationship exists between a particular exposure and particular health effects. When the exposure is via the air, as is the case with environmental tobacco smoke (ETS) exposure to nonsmokers, the organs that are directly exposed include the eyes, nose, throat, and lungs. Clinical, epidemiologic, and animal studies have shown, generally speaking, that air pollutants can have major health effects on the respiratory system (National Research Council, 1985). Experimental research using animals (Chapter 3) and research with biological markers in humans (Chapter 8) indicate that various constituents of the smoke are absorbed into the blood and, therefore, are transported to organs and tissues of the body. Consequently, the range of possible health effects of exposure to ETS may be very broad and vary enormously in their effect on the individual. Effects may be reversible or irreversible, discomforting, or life-threatening. In the following chapters, several possible health effects that have received substantial attention are reviewed. Many of the health effects associated with active smoking have been evaluated in studies of nonsmokers exposed to ETS. These include: acute, noxious sensory irritation; nonmalignant respiratory symptoms and disease; decrease in pulmonary function; lung and other cancers; cardiovascular disease; relative growth, ear infections in children; and low birthweight of children of nonsmoking women. Nonsmokers commonly complain of the perception of tobacco smoke and its irritating, noxious, or annoying qualities. However, in most such spontaneous instances, these complaints are voiced

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Environmental Tobacco Smoke: Measuring Exposures and Assessing Health Effects because the subjects can see another person actively smoking in their vicinity. Chapter 10 reviews experimental studies that evaluate these acute comfort aspects under controlled conditions. Chapters 11 and 12 assess and evaluate possible nonneoplastic and neoplastic pulmonary effects of exposure to ETS by nonsmokers. Over the past 15 years, a number of studies in children and in adults have assessed various possible acute and chronic pulmonary effects subsequent to long-term exposure to ETS. Individuals who have chronic lung diseases, such as patients with asthma, alpha-l-antitrypsin deficiency, or cystic fibrosis, are potentially hypersensitive to the effects of ETS exposures. Chapter 13 reviews and evaluates reports of cancers other than lung that may be associated with exposure to ETS in nonsmokers. Chapter 14 discusses the possible association of exposure to ETS with chronic and acute cardiovascular responses and cardiovascular diseases in nonsmokers. Individuals with chronic disease that compromise the cardiovascular system, such as patients with a history of angina pectoris, are at a high risk for developing abnormal cardiovascular responses following exposure. Chapter 15 considers evidence that a number of other health effects are linked to ETS exposure in children of smokers, including lower relative growth, frequency of ear infections, and low birthweight (with nonsmoking pregnant mothers). The studies reviewed here are epidemiologic and experimental. Epidemiologic studies include case-control studies, in which subjects are selected according to whether or not they have the health outcome being studied, and cohort (or prospective) studies, in which subjects are classified according to whether or not they have been exposed to ETS. Cross-sectional studies are those in which an assessment is made of a population at one point in time. Longitudinal studies follow a group of persons over time. In experimental studies, subjects are exposed to ETS under controlled conditions often using chamber studies. Most studies of ETS have been cross-sectional rather than longitudinal. To be informative, a study must evaluate a sufficient number of people to provide a precise estimate of the effect; obtain valid information regarding the history of exposure and health status of the individuals; and, of course, the statistical analyses must be appropriate to the study design. The appropriate design and use of these epidemiologic methods for the study of air pollution and possible health effects

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Environmental Tobacco Smoke: Measuring Exposures and Assessing Health Effects are discussed in general terms in the monograph “Epidemiology and Air Pollution” (National Research Council, 1985). REFERENCE National Research Council, Committee on the Epidemiology of Air Pollutants. Epidemiology and Air Pollution. Washington, D.C.: National Academy Press, 1985. 224 pp.