As many as 4% of population-level asthma cases could be attributed to secondhand smoke, the study suggests.
Exposure to secondhand smoke increases a person’s risk of respiratory diseases like asthma and chronic obstructive pulmonary disease (COPD) regardless of whether the person is exposed as a child, an adult, or both.
The new report helps unify existing knowledge about links between “passive smoking” and the health consequences associated with personal use of cigarettes and other tobacco products.
Corresponding author Morten Dahl, MD, PhD, of Zealand University Hospital, in Denmark, and colleagues said second-hand smoking has been the topic of considerable research in children, because a child’s lungs are still in development and therefore could be particularly harmed by exposure to smoke. However, research has also suggested that adults who are regularly exposed to cigarette smoke are also at risk. In an attempt to better understand how secondhand smoke affects people at different ages in their lives, the investigators pulled data from a cohort of more than 20,000 adults who participated in the Danish General Suburban Population Study, a cross-sectional study performed in a Danish city between 2010 and 2013. Their findings were published in the Journal of Asthma and Allergy.
The database yielded 2551 patients (12%) who had been exposed to secondhand smoke for their entire lives, 459 patients (2%) who had only been exposed to secondhand smoke as adults, and 13,998 (69%) who were exposed in childhood only. At the time of the study, all 3 groups of patients had mean ages in the mid-50s.
A minority of members of each age cohort were reported to be current smokers: 25% of those in the lifelong secondhand smoke exposure group, 20% in the adulthood-only group, and 18% in the childhood-only group. For comparison, among 3413 people in the database who had never been exposed to secondhand smoke, just 12% were current smokers.
The investigators then examined the groups to determine rates of common respiratory conditions, such as wheezing, severe dyspnoea, coughing on exertion, asthma, and COPD. In all cases, exposure to secondhand smoke increased the odds ratios of having the respiratory condition.
In the case of asthma, the odds ratios (OR) for those with lifelong exposure, adulthood-only exposure, and childhood-only exposure were 1.36 (95% CI, 1.14–1.63), 1.49 (95% CI, 1.09–2.05), and 1.13 (95% CI, 0.99–1.30), respectively. For COPD, the odds ratios were 1.24 (95% CI, 1.03–1.48), 1.25 (95% CI, 0.90–1.74), and 1.09 (95% CI, 0.96–1.24), respectively.
“The main finding of this study is of a dose-response relation between exposure to secondhand smoking and respiratory symptoms, pulmonary function, and risk of asthma in the general population,” the authors said.
Extrapolating those data, the investigators concluded that 4.3% of population-level cases of asthma and 2.9% of population-level cases of COPD could potentially be attributed to lifelong secondhand smoke exposure.
The authors noted several limitations. One limitation of their study is that secondhand smoking exposure was self-reported. They said it is possible that recall bias affected some of the results. They also said their data did not include the number of smokers in a household, and so the risk could be higher in households with multiple smokers. They added that it is also possible that there was misclassification of COPD in some cases.
Finally, they noted that their data were based on a Danish population, and therefore its findings may not be generalizable to all other populations.
Still, the authors said their findings generally align with previous research and underscore the case that the health consequences of smoking are not limited to the smoker.
Korsbæk N, Landt EM, Dahl M. Second-hand smoke exposure associated with risk of respiratory symptoms, asthma, and COPD in 20,421 adults from the general population. J Asthma Allergy. Published online October 28, 2021. doi:10.2147/JAA.S328748