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Article Excerpt
OBJECTIVE: The purpose of this study was to examine the association of exposures to tobacco smoke and environmental lead with attention deficit hyperactivity disorder (ADHD).
METHODS: Data were obtained from the National Health and Nutrition Examination Survey 1999-2002. Prenatal and postnatal tobacco exposure was based on parent report; lead exposure was measured using blood lead concentration. ADHD was defined as having current stimulant medication use and parent report of ADHD diagnosed by a doctor or health professional.
RESULTS: Of 4,704 children 4-15 years of age, 4.2% were reported to have ADHD and stimulant medication use, equivalent to 1.8 million children in the United States. In multivariable analysis, prenatal tobacco exposure [odds ratio (OR) = 2.5; 95% confidence interval (CI), 1.2-5.2] and higher blood lead concentration (first vs. fifth quintile, OR = 4.1; 95% CI, 1.2-14.0) were significantly associated with ADHD. Postnatal tobacco smoke exposure was not associated with ADHD (OR = 0.6; 95% CI, 0.3-1.3; p = 0.22). If causally linked, these data suggest that prenatal tobacco exposure accounts for 270,000 excess cases of ADHD, and lead exposure accounts for 290,000 excess cases of ADHD in U.S. children.
CONCLUSIONS: We conclude that exposure to prenatal tobacco and environmental lead are risk factors for ADHD in U.S. children.
KEY WORDS: ADHD, attention deficit hyperactivity disorder, blood lead, children, environmental tobacco smoke, lead poisoning, NHANES, prenatal tobacco exposure, tobacco. Environ Health Perspect 114:1904-1909 (2006). doi:10.1289/ehp.9478 available via http://dx.doi.org/ [Online 19 September 2006]
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Attention deficit hyperactivity disorder (ADHD) is one of the most common childhood disorders, with an estimated prevalence ranging from 3 to 8% [American Psychiatric Association (APA) 1994; Costello et al. 2003; Lesesne et al. 2003; Olfson et al. 2003; Pastor and Reuben 2002; Rowland et al. 2002; Wolraich et al. 1996]. Children who have ADHD are at increased risk for conduct disorder, antisocial behavior, and drug abuse later in life (Costello et al. 2003; Mannuzza 1993). Moreover, the costs associated with their medical care and education are substantial (Leibson et al. 2001). Although the mechanisms for the development of ADHD remain unclear, both genetic and environmental factors have been implicated (Ernst et al. 2001).
Numerous studies have found a significant association between prenatal environmental tobacco smoke (ETS) exposure and ADHD or ADHD-related behaviors, even after controlling for postnatal ETS exposures and familial psychopathology (Day et al. 2000; Fergusson et al 1993b; Kotimaa et al. 2003; Leech et al. 1999; Mick et al. 2002a; Milberger et al. 1996, 1998; Thapar et al. 2003; Wasserman et al. 2001; Williams et al. 1998). In case-control studies, investigators have found a 2-to 4-fold increased risk for ADHD associated with prenatal ETS exposure (Mick et al. 2002a; Milberger et al. 1996, 1998). In contrast, the relationship between postnatal ETS exposure and children's behavior problems has not been fully elucidated (Day et al. 2000; Fergusson et al 1993b; Weitzman et al. 1992; Williams et al. 1998). Moreover, the attributable fraction of childhood ADHD due to ETS exposure is unknown.
Environmental lead exposure, measured in blood or dentin, has been associated with higher rates of inattention and impulsivity (Bellinger et al. 1994; Fergusson et al. 1993a; Needleman et al. 1979; Wasserman et al. 1998, 2001). Although lead exposure is often cited as a risk factor for ADHD, existing studies examining the association of lead exposure with a diagnosis of ADHD, which were limited by small sample size, are inconclusive (David et al. 1972; Gittleman and Eskenazi 1983). Moreover, many of the studies examining the association of lead exposure with inattention or impulsivity involved children who had higher blood lead levels than the levels seen in contemporary children, and thus may not be directly relevant to children with lower levels of lead exposure (Bellinger et al. 1994; Needleman et al. 1979; Fergusson et al. 1993a; Wasserman et al. 1998, 2001). Although several recent studies have linked lead to IQ deficits at blood lead levels < 10 [micro]g/dL (Bellinger and Needleman 2003; Canfield et al. 2003; Lanphear et al. 2005)--the current action level set by the Centers for Disease Control and Prevention (CDC)--it remains unclear whether blood lead levels < 10 [micro]g/dL are also associated with behavioral problems in children (CDC 2005b).
Studies investigating the effect of environmental exposures on neurobehavioral outcomes have been complicated by evidence from both animal and human studies that toxicants may have differing effects in male and female subjects (Burns et al. 1999; Ernst 2001; McCartney 1999; O'Callaghan et al. 1992; Ribary and Lichtensteiger 1989; Ris et al. 2004; Weissman et al. 1999). The prevalence of ADHD is three times greater among males than among females (Costello et al. 2003; Lesesne et al. 2003; Olfson et al. 2003; Pastor and Reuben 2002). Some studies have documented varying behavioral effects of prenatal ETS exposure in males and females (Fergusson et al. 1998; Weissman et al. 1999), whereas other studies have not (Mick et al. 2002a; Milberger et al. 1996, 1998; Orlebeke et al. 1999). Studies of lead exposure's effects have been similarly complicated: There is some evidence that males are at increased risk for externalizing behaviors (Burns et al. 1999) and attentional problems (Ris et al. 2004) from lead exposure, but the results are not entirely consistent.
The purpose of this study was to explore the relationship between exposure to ETS and environmental lead with ADHD using a large nationally representative sample of children. We also explored whether sex modifies the relationships between these neurotoxicants and ADHD. Finally we provide estimates of population attributable fraction of prenatal ETS exposure and lead exposure for ADHD in U.S. children.
Methods
Data source. The data for this analysis came from the National Health and Nutrition Examination Survey (NHANES), conducted from 1999 to 2002. The NHANES is a cross-sectional household survey of the noninstitutionalized civilian population. NHANES used a complex, multistage probability sampling design, with oversampling of children (< 5...
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