Wheeze, Asthma in Children Linked to Passive Smoke Exposure

Posted: 3/19/2012

From Pediatrics:

Children who are exposed to tobacco smoke prenatally or in their home after birth are at least 20% more likely to have wheezing episodes or develop asthma. The magnitude of the risks is higher than seen in previous estimates, according to a meta-analysis published online March 19 in Pediatrics.

Hannah Burke, BMBS, from the University of Nottingham in the United Kingdom, and colleagues conducted a systematic review and meta-analysis of 71 prospective epidemiologic studies that examined the association between passive smoke exposure and the incidence of pediatric wheeze and asthma.

After conducting an extensive literature search that included Medline, Embase, and the Cumulative Index to Nursing and Allied Health Literature, as well as conference abstracts, they identified and screened 5074 articles, yielding 70 articles with a total of 71 studies.

"We included all prospective epidemiologic studies assessing the association between passive smoke exposure and incidence of asthma or wheeze in children or young people up to the age of 18 years in which participants were free of disease (asthma or wheeze) at the start of the study and passive smoke exposure was documented at a time point before the incidence of disease was determined," the authors write.
The researchers analyzed the effects of 4 different types of smoke exposure on the development of wheezing and asthma: prenatal maternal smoking, maternal smoking, paternal smoking, and household smoke exposure.

Prenatal Maternal Smoking

Prenatal maternal smoke exposure was associated with a 40% increase in risk for wheeze in children aged 2 years or younger (odds ratio [OR], 1.41, 95% CI, 1.20 - 1.67; I2, 82.5%; 14 studies). Results were similar for children aged 3 to 4 years (OR, 1.28; 95% CI, 1.14 - 1.44; I2, 65.5%; 8 studies). This exposure also was associated with a 52% increased risk of wheezing in children aged 5 to 18 years (OR, 1.52; 95% CI, 1.23 - 1.87; I2, 21.1%; 5 studies).

In addition, prenatal smoke exposure was associated with an increased risk for asthma; this risk was highest in children aged 2 years or younger (OR, 1.85; 95% CI, 1.35 - 2.53; I2, 41.9%; 5 studies).

Risks declined progressively with age, but children aged 5 to 18 years still had an increased risk of developing asthma (OR, 1.23; 95% CI, 1.12 - 1.36; I2, 50%; 11 studies).

Maternal Smoking

Postnatal maternal smoke exposure was associated with an increased risk for wheezing episode in children aged 2 years or younger (OR, 1.70; 95% CI, 1.24 - 2.35; I2, 0.0%; 4 studies), in children aged 3 to 4 years (OR, 1.65; 95% CI, 1.20 - 2.28; I2, 48.5%; 4 studies), and in children aged 5 to 18 years (OR, 1.18; 95% CI, 0.99 - 1.40; I2, 1.4%; 3 studies).

Postnatal maternal smoke exposure was not associated with increased risk for asthma in children aged 4 years or younger, but there was a borderline association for children 5 to 18 years of age (OR, 1.20; 95% CI, 0.98 - 1.46; P = .08; I2, 65.3%; 8 studies).

Paternal Smoking

There were limited data on paternal smoking, with only 2 studies available for analysis of risk of wheezing in children 5 to 18 years of age (OR, 1.38; 95% CI, 1.05 - 1.85; I2, 0%; 2 studies).

No studies had data on the association between paternal smoke exposure and the risk for asthma in children 2 years of age of younger, and there was only 1 study with data on children 3 to 4 years of age. That study showed a significant effect of paternal smoking (OR, 1.34; 95% CI, 1.23 - 1.46).

There was no association between paternal smoke exposure and development of asthma in children aged 5 to 18 years (OR, 0.98; 95% CI, 0.71 - 1.36; I2, 0%; 4 studies).

Household Smoke Exposure

Exposure to household smoke was associated with an increased risk of wheezing in children aged 2 years or younger (OR, 1.35; 95% CI, 1.10 - 1.64; I2, 64.5%; 9 studies).

Household smoke exposure was not associated with an increased risk of wheezing in children aged 3 to 4 years (OR, 1.06; 95% CI, 0.88 - 1.27; I2, 54.5%; 4 studies), but it was associated with an increased risk of wheezing in children aged 5 to 18 years (OR, 1.32; 95% CI, 1.12 - 1.56; I2, 1.7%; 5 studies).

Exposure to household smoke was not associated with an increased risk for asthma in children 2 years of age or younger (OR, 1.14; 95% CI, 0.94 - 1.38; I2, 1.7%; 3 studies), but it was associated with an increased risk for asthma in children aged 3 to 4 years (OR, 1.21; 95% CI, 1.00 - 1.47; I2, 72.7%; 5 studies) and children aged 5 to 18 years (OR, 1.30; 95% CI, 1.04 - 1.62; I2, 37.7%; 5 studies).

Effects of Passive Smoke Higher Than Previous Estimates

"Our findings indicate that the effects of passive smoking on the incidence of wheeze and asthma are substantially higher than previously estimated, particularly for the effect of maternal postnatal smoking exposure," the authors write.

The authors note that this systematic review and meta-analysis is the largest reported review of this subject to date.

"Exposure to passive smoking is an important risk factor for the incidence of wheeze and asthma throughout childhood.... [I]t is important to limit children's exposure to passive smoke both during gestation and throughout the child's life," the authors write.

This study was supported by a project grant from Cancer Research UK and by core funding to the UK Centre for Tobacco Control Studies from the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council, and the Department of Health, under the auspices of the UK Clinical Research Collaboration. The authors have disclosed no relevant financial relationships.