Attention deficit hyperactivity disorder (ADHD) is one of the most common childhood disorders, but it can extend beyond childhood into adolescence and adulthood. People with this disorder exhibit symptoms of inattention, hyperactivity, and impulsivity, which further extend into difficulty staying focused and paying attention, difficulty controlling behavior, and being over-active.
Studies show that the number of children diagnosed with ADHD is increasing, but it is unclear why. It is known that ADHD is a heritable neurodevelopmental condition, but there has been recent interest in the potential environmental impact on the onset of the disorder. Certain neurotoxins found in the environment are sources for psychological and developmental issues. In particular, lead is one environmental neurotoxicant known to severely interfere with brain development. It affects many different areas of the brain including the cerebral cortex, cerebellum and hippocampus. In children, lead exposure has been associated with reduced IQ, learning disabilities, decreased growth, hyperactive and antisocial behavior, and impaired hearing.Even low-level exposure to lead has been associated with reduced intelligence, impaired attention, and behavioral problems. Thus, the exposure to lead in the environment has been a recent subject of interest.
Image Source: Peter Dazeley
A research team in the department of Psychiatry and Behavioral Neuroscience at Oregon Health and Science University conducted a study to evaluate the possible correlation between lead exposure and ADHD. In the study, they examined the association between ADHD symptoms in children and blood lead levels as moderated by a particular gene. This gene, known as HFE, is known to regulate the uptake of iron and control lead metabolism. Thus, it was hypothesized that altering the HFE genotype would alter the magnitude of blood lead and ADHD symptom association. A population of roughly 386 healthy children aged six to 17 were used as test subjects; their blood lead concentrations were measured, and variables such as IQ scores, teacher and parent ratings of ADHD symptoms, and measures of inattention and impulsivity, were quantified. The researchers then plotted their blood lead concentrations against these factors, as a multivariable linear regression.
The analysis of this study showed a heightened causal link between lead exposure and ADHD symptoms, particularly hyperactivity-impulsivity, in those with the HFE gene mutation. This mutation is present in approximately 10% of US children. The study also found that lead effects were more robust in males, which is consistent with previous research specific to neurodevelopmental conditions and gender. Children without HFE mutations showed amplified symptoms as lead exposure increased, but not as consistently. Therefore, this study demonstrates that environmental pollutants, such as lead, do play a role in the explanation of ADHD.
Feature Image Source: ADHD by Practical Cures
