Academic journal article Iranian Journal of Psychiatry

The Role of Lead Exposure on Attention-Deficit/ Hyperactivity Disorder in Children: A Systematic Review

Academic journal article Iranian Journal of Psychiatry

The Role of Lead Exposure on Attention-Deficit/ Hyperactivity Disorder in Children: A Systematic Review

Article excerpt

Attention deficit / hyperactivity disorder (ADHD) is one of the most commonly diagnosed psychiatric disorders in children. In addition, it is probably the most common chronic condition undiagnosed in adults (1, 2). According to the American Psychiatric Association's Diagnostic and Statistical Manual Fifth Edition, 3 to 7% of children in school and 2 to 4% of the adult population have ADHD (3, 4). The global statistics show that about 10.1% of the world's population has ADHD (5), making this disorder an important health issue. This disorder continues to about 50 to 80% of teenagers and 15 to 65% of adults (6, 7). Moreover, ADHD is more prevalent in boys than girls (9). Children are more exposed to psychiatric disorders such as antisocial personality (9), depression, unipolar depression (10), bipolar (11), anxiety, autism, learning disabilities, emotional disturbance, and fiery temperament (9, 12 and 13). The tendency for drug use and addiction increases in adults if the disorder is not diagnosed and treated at a younger age (14). Some ADHD symptoms disappear with time, but the symptoms such as lack of concentration are constant and a person will be show them throughout their lifetime (13). Therefore, considering the implications, the efforts for early diagnosis of the disease is crucial, and identifying the contributing factors is of prime importance to prevent ADHD.

Biological and environmental factors are the pathogenesis of this disorder, including head injury, a decrease in the prefrontal cortex, and toxins and chemicals found in the environment (15). Although evidence shows that ADHD is a familial problem, many environmental risk factors such as exposure to heavy metals, Dietary factors, environmental exposure to dangerous chemicals such as bisphenol A, polycyclic aromatic compounds, pesticides intensify or accelerate the progression of this disease (16-18).

Lead (Pb) metal as a neurotoxin has been causing abnormal behavior in children, and many studies have examined the relationship between exposure to heavy metals and other harmful environmental factors in the pathogenesis (19-21). Since 1960, the CDC recommended levels for blood lead levels in children have been steadily reduced, and this has been due to increased researches showing that it has negative effects on health. Currently, the children's blood lead level (BLL) is set to 10 micrograms of lead per deciliter of blood (µg/dL), and it has not been changed since 1991 (22). The CDC action level set for lead may be outdated now as recent research indicates that adverse health effects may be associated with blood lead levels below 10µg/dL. Many studies have been conducted on cognitive problems in children including reduced IQ scores, math, reading, verbal memory, and spatial ability, with blood lead levels below 10µg/dL. Recent trends showed a 3% increase in the diagnosis of attention deficit/ hyperactivity disorder (ADHD) in each year from 1997 to 2006 (23). Researchers are investigating whether exposure to lead contributes to an increase in the number of ADHD cases.

A systematic review was conducted to have a clear answer and deep understanding of the topic of concern. Among all the heavy metals, Lead is one of the significant heavy metals causing mental illness. In order to have a clear and deep understanding of the effects of lead on the mental health of children, lead was selected as the main element for the systematic review in this paper. The aim of this study was to systematically review all the studies showing the relationship between ADHD symptoms and blood lead levels below 10µg/dL in children. The findings of these studies also account for the gaps and research needs. Synthesizing the evidence related to ADHD symptoms in children with BLLs less than 10µg/dL will help determine whether the current BLL is still appropriate for children or not.

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National and international databases, such as PubMed, PsycINFO, Web of Science, SID, IRAN Medex, IRAN DOC, were searched. …

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