Prolonged exposure to in adulthood, new research has found.
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With data from 70,900 never-smoking men and women, most aged 50 years or over, in the Cancer Prevention Study–II Nutrition Cohort, researchers examined associations between childhood and adult secondhand smoke exposure and the risk of death during adulthood from all causes, heart disease, stroke, and COPD. Participants were followed from enrollment in 1992-1993 to 2016-2017.
In a paper published in the September issue of the American Journal of Preventive Medicine, they reported that individuals who had lived with a smoker throughout childhood (16-18 years) had a 31% higher risk of dying from COPD, compared with individuals not exposed to secondhand smoke during childhood (95% confidence interval 1.05-1.65, P = .06). Any exposure to secondhand smoke in childhood – defined as one or more hours of exposure per week – was associated with a 21% higher risk of COPD mortality.
“It is established that SHS [secondhand smoke] exposure in childhood can result in asthma, chronic wheezing, respiratory infections, and decreased lung function and growth in children,” wrote W. Ryan Diver, a cancer epidemiologist, and his colleagues from the Epidemiology Research Program at the American Cancer Society. “These respiratory illnesses in early life are associated with worse lung function in adolescence and adulthood, as indicated by a lower forced expiratory volume in a 1 second plateau, and ultimately diagnosis of COPD.”
The researchers did not see a significant association between childhood secondhand smoke exposure and the risk of death from ischemic heart disease or stroke in adulthood. But the authors said that there was compelling evidence that secondhand smoke exposure during childhood contributed to increased arterial stiffness, autonomic dysfunction, and other vascular effects, which had led to the hypothesis that such exposure might influence the risk of heart disease and stroke mortality in adulthood. They suggested that this effect might have been more apparent in generations born in the 1950s and 1960s, where both parents were likely to smoke at home, as opposed to just one parent, which would have meant higher levels of exposure to secondhand smoke.
Adult exposure to secondhand smoke showed a significant dose-response relationship with overall mortality. Those exposed for 10 or more hours a week showed a 9% higher risk of death from all causes (95% CI 1.04-1.14, P less than .0001), as well as a significant 27% higher risk of death from ischemic heart disease.
Any exposure to secondhand smoke in adulthood was associated with a 14% higher risk of stroke, with a trend of increasing risk with increasing exposure.
The researchers also saw a significant association between secondhand smoke exposure and COPD mortality, but only in adults who reported being exposed both outside and inside the home.
The authors noted that the most recent Surgeon General’s report found that the evidence on secondhand smoke and increased risk of death from COPD was “suggestive but not sufficient,” and further research was needed.
“The associations observed with both childhood exposure to SHS and adult exposure to SHS add to the mounting data relating SHS to COPD,” they wrote.
One limitation of the study was that it relied on self-report, which in the case of childhood exposure would have required some participants to recall at least 3 decades back. It also did not capture whether it was the mother or father who smoked, which meant the authors could not account for possible effects of smoking during pregnancy.
The investigators noted that “more than 50 years after the publication of the first Surgeon General report on smoking and health, these findings suggest that researchers and scientists still do not fully understand the long-term health consequences of smoking, particularly, the potential delayed effects of childhood SHS exposure in later adulthood.” Despite this, the authors said the findings “provide further support for implementation of smoke-free air laws, smoke-free home policies, and clinical interventions to reduce SHS exposure.”
No conflicts of interest were declared.
SOURCE: Diver WR et al. Am J Prev Med 2018;55[3]:345-52. doi: 10.1016/j.amepre.2018.05.005.