Tobacco Smoke and Lead Exposure Responsible for Half a Million Cases of ADHD?

Research conducted at a Cincinnati children’s hospital reveals a correlation between prenatal tobacco exposure and ADHD, and between higher blood levels of lead and ADHD. Could these two factors be responsible for over half a million cases of attention deficit hyperactivity disorder in the US alone?

Here are the details, straight from the abstract of ‘Exposures to Environmental Toxicants and Attention Deficit Hyperactivity Disorder in US Children‘, published earlier this week in the journal Environmental Health Perspectives.

Note: these results are specifically correlational, meaning that a causal connection has not been established. In other words, although prenatal tobacco smoke and lead are strongly implicated as risk factors for ADHD, this research does not show that either prenatal tobacco smoke or lead exposure definitely do cause ADHD.

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 was 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 current stimulant medication use and parent report of ADHD diagnosed by a doctor or health professional.

Results: Of 4,704 children age 4 to 15 years, 4.2% were reported to have ADHD and stimulant medication use, equivalent to 1.8 million children in the U.S. In multivariable analysis, prenatal tobacco exposure (Odds Ratio [OR]: 2.5; 95% 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.

Also of note, the fifth quintile for blood lead concentration began at 2 micrograms per decilitre, while the US government’s ‘acceptable’ blood lead level is currently 10 micrograms per decilitre. Over 300 thousand US children ages 1 to 5 were estimated to have levels exceeding that higher threshold.

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