Attention deficit hyperactivity disorder among children exposed to secondhand smoke: A logistic regression analysis of secondary data

Abstract

Background

A growing body of literature examines the association of postnatal secondhand smoke exposure with attention deficit hyperactivity disorder (ADHD) in children, but the findings are mixed.

Objective

We compare prevalence of ADHD in children aged 4–15 years who were exposed to postnatal secondhand smoke with prevalence in those who were not exposed, and examine the association of postnatal secondhand smoke exposure with ADHD using both reported and cotinine-measured secondhand smoke exposure.

Design and setting

We analyze secondary data from the 1999–2004 U.S. National Health and Nutrition Examination Surveys.

Participants

Analyses using reported secondhand smoke exposure and cotinine-measured exposure included 6283 and 6033 children aged 4–15 respectively, including 419 and 404 children who either had a reported physician diagnosis of ADHD or were taking stimulant medications.

Methods

The association of secondhand smoke exposure with ADHD was examined by two multiple logistic regression models that differ in the secondhand smoke measurement used.

Results

After controlling for maternal smoking during pregnancy, gender, age, race/ethnicity, preschool attendance, health insurance coverage, and exposure to lead, children with reported secondhand smoke exposure at home were more likely to have ADHD (adjusted odds ratio = 1.5, 95% confidence interval: 1.1-2.0) than those who were not exposed. After controlling for these covariates, children with detectable cotinine levels were more likely to have ADHD (adjusted odds ratio = 1.8, 95% confidence interval: 1.3-2.5) than those with non-detectable levels.

Conclusions

Our findings suggest that secondhand smoke exposure in children is strongly associated with ADHD independent of other risk factors and this association is robust using both measurements of secondhand smoke exposure. Further research is needed to understand the mechanism underlying this association. Nurses and other healthcare professionals can play an important role in encouraging parents to quit smoking to reduce children's exposure to secondhand smoke and their risk of ADHD.

Introduction

Despite the documented harm of secondhand smoke exposure for children's physical health (California Environmental Protection Agency, 2005, U.S Department of Health and Human Services, 2006), many children still live with smokers and are exposed to secondhand smoke. In the US in 2005-06, 14.6% of children aged 3-11 lived in homes with smokers and 50.9% of them had detectable serum cotinine (>.05 ng/mL), a metabolite of nicotine. Their geometric mean cotinine level was .11 ng/mL (Max et al., 2009). Internationally, it has been estimated that more than half of all children are exposed to secondhand smoke in their homes (International Consultation on Environmental Tobacco Smoke and Child Health, 1999). Findings from the Global Youth Tobacco Surveys, conducted among students in 132 countries in 1999-2005, indicate that 44% of respondents were exposed to secondhand smoke at home, 56% were exposed in public places, and 47% had parents who smoked (The GTSS Collaborative Group, 2006).

Recently, there has been a growing body of literature linking secondhand smoke exposure, also referred to as environmental tobacco smoke exposure, to children's mental health outcomes (Bandiera et al., 2011, Froehlich et al., 2009, Yolton et al., 2005). One such outcome, attention deficit hyperactivity disorder (ADHD), is a behavioral disorder characterized by a pervasive pattern of hyperactivity-impulsivity and/or inattention. ADHD has become an increasingly common diagnosis in children (Boyle et al., 2011, CDC, 2010) and has been found to increase with age at least through the mid-teenage years (Braun et al., 2006, Froehlich et al., 2009, Kabir et al., 2011). Nurses, particularly school nurses and those in outpatient settings, have played an important role in both the identification and management of ADHD in children (Foreman and Morton, 2011, Krause-Parello and Samms, 2010, Thompson and Ni Bhrolchain, 2011).

Most studies linking secondhand smoke exposure to ADHD in children focus on maternal smoking during pregnancy and find consistent evidence supporting a significantly adverse effect (Hermann et al., 2008, Langley et al., 2005, Schmitz et al., 2006). However, studies examining the association of postnatal secondhand smoke exposure with ADHD are less conclusive. In a 2005 report by the California Environmental Protection Agency (EPA) (California Environmental Protection Agency, 2005), an extensive review of the scientific evidence from major U.S. studies led the authors to conclude that “evidence suggesting a link between postnatal environmental tobacco smoke exposure and impaired cognition and behavior was found to be suggestive, although not entirely consistent” (pp. 4-18). Bandiera et al. (2011) reported that postnatal secondhand smoke exposure was positively associated with symptoms of ADHD, but not a diagnosis of ADHD. Kabir et al. (2011) and Xu et al. (2010) both found that postnatal secondhand smoke exposure was associated with higher rates of ADHD. However, two studies found that postnatal secondhand smoke exposure was not associated with ADHD (Braun et al., 2006, Froehlich et al., 2009). These mixed results might be attributed to the differences in methods of determining ADHD status, measurement of postnatal secondhand smoke exposure, data used, sample size, exclusion criteria for study sample, and confounding factors included in the study. For example, there has been emerging evidence suggesting that other environmental exposures are linked to ADHD, including lead (Braun et al., 2006, Froehlich et al., 2009) and organophosphate pesticides (Bouchard et al., 2010), and prenatal exposure to organochlorines (Sagiv et al., 2010). Prenatal alcohol exposure has additionally been suggested as a risk factor for ADHD (Banerjee et al., 2007, Knopik et al., 2005). Also, postnatal secondhand smoke exposure is found to be collinear with prenatal maternal smoking (Eskenazi and Castorina, 1999). Therefore, it is important to control for prenatal maternal smoking and other environmental exposures in order to assess the independent effect of postnatal secondhand smoke exposure on ADHD.

This study compares the prevalence of ADHD in children who are exposed to secondhand smoke with those who are not exposed, and examines the association of postnatal secondhand smoke exposure with ADHD using a large nationally representative sample of U.S. children. While the data analyzed in this study are from the U.S., the issue is of international concern given the widespread smoking prevalence and exposure of children to secondhand smoke globally. We extend the previous research by focusing on children who were nonsmokers; by analyzing the independent impact of secondhand smoke exposure after controlling for prenatal tobacco exposure, other environmental exposures, and socioeconomic factors; and by using both reported and cotinine-measured secondhand smoke exposure.