Abstract

Objectives: The authors assessed the effects of environmental tobacco smoke (ETS) on the development of asthma in adults.
Methods: In the Pirkanmaa district of South Finland, all 21- to 63-year-old adults with new cases of asthma diagnosed during a 2.5-year period (n=521 case patients, out of 441000 inhabitants) and a random sample of control subjects from the source population (932 control subjects) participated in a population-based incident case-control study.
Results: Risk of asthma was related to workplace ETS exposure (adjusted odds ratio [OR]=2.16; 95% confidence interval [CI]=1.26, 3.72) and home exposure (OR=4.77; 95% CI=1.29, 17.7) in the past year. Cumulative ETS exposure over a lifetime at work and at home increased the risk.
Conclusions: This study indicates for the first time that both cumulative lifetime and recent ETS exposures increase the risk of adult-onset asthma.

Introduction

Environmental tobacco smoke (ETS) contains over 4000 compounds, including several carcinogens, irritants, and toxic agents.^[1,2] There is convincing evidence of parental smoking causing asthma in children,^[3,4] but the evidence on ETS exposure and development of adult asthma is limited.^[4,5] This question is of major public health relevance, as the occurrence of both ETS exposure and asthma is relatively common in working-age populations.

Only 6 studies have addressed the question of ETS and asthma in adulthood,^[6-11] indicating an increased risk of asthma in relation to ETS exposure at home,^[7,10,11] at work,^[6,9] or both.^[8] Most of these studies were vulnerable to selection and information bias because of cross-sectional designs or asthma diagnosis being based on self-report. In addition, Robbins and colleagues^[12] reported a study on ETS and airway obstructive disease, including both asthma cases and cases of chronic obstructive pulmonary disease, that was based on the same study population of Californian Seventh Day Adventists as the study by Greer et al. that focused on asthma.^[6] Stronger evidence of the causal role of ETS exposure in asthma among the working population would support more strict preventive measures and health policies in workplaces.

We conducted a large population-based study in South Finland to assess the effect of ETS exposure in the workplace and at home on the development of asthma in the working-age population. We recruited all adults with new cases of asthma in a population of approximately 441000 people over 2.5 years.