Inflammation & Allergy - Drug Targets, 2009, 8, 321-327 321 1871-5281/09 $55.00+.00 © 2009 Bentham Science Publishers Ltd. Epidemiological Evidence Associating Secondhand Smoke Exposure with Cardiovascular Disease Brent E. Faught *,1 , Andreas D. Flouris 2 and John Cairney 3 1 Faculty of Applied Health Sciences, Brock University, Canada 2 Institute of Human Performance and Rehabilitation, Centre for Research and Technology Thessaly, Greece 3 Departments of Family Medicine, Psychiatry and Behavioural Neurosciences & Clinical Epidemiology and Biostatistics, McMaster University, Canada Abstract: The objective of this paper was to review the epidemiological literature examining the association between secondhand smoke (SHS) and cardiovascular disease (CVD). Specifically, we examined the various screening methods available in assessing smoking behaviour and quantifying nicotine absorption. Further, we considered the natural history of those exposed to SHS and the associated risk of CVD. We reviewed routine methods used to assess exposure to SHS; evaluated the utility of subjective screening questions regarding smoking behaviour and examined the efficacy of nicotine and cotinine biomarkers used to quantify SHS exposure in epidemiological and clinical-based research. Self-reporting is practical and cost-effective in identifying smoking behaviour patterns, but is subject to recall bias and underestimation of exposure, especially in the presence of children. Nicotine and cotinine biomarkers have proven valuable in quantifying tobacco smoke absorption and establishing biological plausibility. A combination of SHS self-reported and biomarker evaluation provide the most stringent method of establishing exposure. Sufficient evidence is reported in epidemiological research to support a causal association between SHS exposure and increased risks of CVD morbidity and mortality among both men and women. The risk of developing an acute cardiac syndrome or chronic lifetime coronary events is at least 30%. Similarly, reduction in the incidence of a myocardial infarction decreases by nearly 50% in the absence of SHS. Considering the biological plausibility and dose-response relationship between SHS and CVD, effective interventions that incorporate a comprehensive screening method of behavioral and biological measures of exposure coupled with efficacious treatment should elicit favorable change for at-risk populations. Keywords: Secondhand smoke, cardiovascular disease, epidemiology, screening, exposure, biomarkers, self-reporting, morbidity, mortality. 1. INTRODUCTION Secondhand smoke (SHS), previously known as passive smoking is the involuntary breathing of other people's tobacco smoke, Approximately 5000 chemicals are produced from cigarette smoke; many poisonous [1]. Secondhand smoke increases the risk of cardiovascular disease (CVD) by 30%, based on epidemiological and biological evidence [2]. A 30-minute SHS exposure was found to affect coronary flow velocity reserve in non-smokers, suggesting endothelial dysfunction in coronary circulation [3]. Evidence from cohort [4, 5], case-control [6] designs and meta-analysis [7] have all suggested a longitudinal association between CVD and SHS exposure. Further, clinical-based and animal model research has supported this association by suggested a biological plausibility for prolonged exposure to SHS [8-10]. Nevertheless, controversial evidence also exists with regards to the natural history of SHS exposure and risk of CVD in non-smokers. Lack of an accurate method of assessing SHS exposure has been suggested as a probable reason for the inconsistency in the literature. Exposure misclassification appears to be attributed to proxy measures of exposure that *Address correspondence to this author at the Faculty of Applied Health Sciences, Brock University, St. Catharines, Ontario, L2S 3A1, Canada; E-mail: bfaught@brocku.ca do not account for spousal smoking status [11, 12], exposure source including home and workplace [5, 11] and lack of SHS normative data and/or recognition of quantifying intolerable levels of nicotine differences in pediatric and adult populations [13]. Valid and efficient means of objectifying secondhand smoke exposure would lead to more thorough surveillance techniques of estimating the risk of cardiovascular disease. This epidemiological review will address the current literature as it applies to quantifying SHS exposure and the natural history of cardiovascular disease among those exposed to secondhand smoke. 2. MEASURING SECONDHAND SMOKE EXPOSURE Secondhand smoke is a controversial issue in public health, particularly since laws governing the right to smoke in community environments are felt to infringe the rights of those who smoke, while protecting the health of non- smokers. Public policy is, at times, established based on epidemiological research. However, observational studies, the mainstay of most epidemiological research, pose significant methodological challenges, which in turn often threaten both the internal and external validity of the results. Specifically, validity of studies in cardiovascular disease and SHS is the ability to accurately estimate tobacco smoke exposure and absorption. Secondhand smoke exposure lacks a true screening or reference standard and is an area of research that requires specific attention when interpreting