Childhood Secondhand Smoke Exposure Ups Risk for Lung Death

Liam Davenport

August 16, 2018

Exposure to secondhand smoke throughout childhood may increase the risk for death from chronic obstructive pulmonary disease (COPD) in adults, even if they never smoke, say US researchers. They also found that adult exposure among never-smokers is linked to death from several conditions.

Analyzing data from a large US cohort, W. Ryan Diver, MSPH, Epidemiology Research Program, American Cancer Society, Atlanta, Georgia, and colleagues found that exposure to secondhand smoke during childhood increased the risk for death from COPD by 31%.

They estimate that this corresponds to an additional 7 deaths per year from COPD per 100,000 people who have never smoked. The study did not look at cases of nonfatal COPD.

The research, published in the American Journal of Preventive Medicine on August 16, also showed that adult secondhand smoke exposure of at least 10 hours per week increased the risk for all-cause death by 9%, death from ischemic heart disease (IHD) by 27%, from stroke by 23%, and from COPD by 42%.

"This is the first study to identify an association between childhood exposure to secondhand smoke and death from chronic obstructive pulmonary disease in middle age and beyond," Diver said in a press statement.

"The results also suggest that adult secondhand smoke exposure increases the risk of chronic obstructive pulmonary disease death," he added. "Overall, our findings provide further evidence for reducing secondhand smoke exposure throughout life."

Study Details

Both parental smoking and exposure to secondhand smoke during childhood are linked to adverse effects during childhood, such as an increased risk for chronic respiratory symptoms, asthma, and poorer lung function.

It has also been suggested that such exposure is associated with developmental effects on the cardiovascular system, including increased blood pressure and poor vascular endothelial function.

Noting, however, that it is unknown whether childhood exposure to secondhand smoke is associated with adult mortality, the researchers examined data from the American Cancer Society's Cancer Prevention Study–II (CPS-II) Nutrition Cohort.

Participants in this subcohort of the CPS-II study were recruited in 1992–1993 from 21 US states, when they were primarily age 50 to 74 years.

They completed a questionnaire on demographic, environmental, occupational, and dietary factors at study entry, with follow-up questionnaires on exposure information sent every 2 years from 1997.

The current analysis focused on never-smokers for whom information on childhood and adult secondhand smoke exposure was available, which yielded 70,900 individuals. They were followed up to the end of 2014, during which period (22 to 23 years) there were 25,899 deaths.

The team notes that around half (52%) of the participants lived with a smoker at some point during childhood, and among this subgroup, most (74%) lived with a smoker for their entire childhood.

People living with smokers during childhood were more likely to be women, less educated, and alcohol drinkers and also more likely to be exposed to secondhand smoke as adults.

Overall, there was no association between any definition of exposure to secondhand smoke during childhood and al-cause mortality or mortality from IHD or stroke.

However, childhood smoke exposure throughout childhood up to 16 to 18 years of age was associated with a significantly increased risk for death from COPD, at a hazard ratio of 1.31, although the overall trend was not significant (P = .06 for trend).

Adult exposure to secondhand smoke was associated with a significantly increased risk for overall mortality (P < .0001 for trend), with the strongest association seen for at 10 or more hours per week of exposure vs no exposure, at a hazard ratio of 1.09.

In addition, adult secondhand exposure was associated with a significantly increased risk for IHD death (P < .0001 for trend), at a hazard ratio for 10 or more hours per week of exposure of 1.27.

Any adult exposure to secondhand smoke was also linked to an increased risk for fatal stroke, at a hazard ratio of 1.14, with a trend for increasing hours of exposure (P = .02).

As expected, there was an association between adult secondhand smoke exposure and death from COPD, at a hazard ratio for 10 or more hours per week of exposure vs no exposure of 1.42, although the trend was not significant (P = .43 for trend).

The researchers acknowledge several limitations to the study, including that childhood secondhand smoke exposure was self-reported at least three decades after childhood and that it was not possible to distinguish between maternal and paternal sources of exposure.

"However, most participants with childhood SHS [second-hand smoke] exposure reported only one smoker in their household during childhood," they write.

"This smoker is more likely to have been their father than their mother given the much higher prevalence of smoking among U.S. men than women through the 1950s."

Summarizing, the team says 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.

"Understanding these long-term effects [is] relevant in the US, and potentially even more relevant in countries where smoking rates and SHS exposure are higher."

They also believe that the results "provide further support for implementation of smoke-free air laws, smoke-free home policies, and clinical interventions to reduce SHS exposure."

The American Cancer Society funds the creation, maintenance, and updating of the CPS-II cohort. The authors have disclosed no relevant financial relationships.

Am J Prev Med. 2018;55:345-352. Full text

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