Environmental risk factors for attention‐deficit hyperactivity disorder
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Acta Pædiatrica
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2007-06-15
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Abstract
Attention-deficit hyperactivity disorder (ADHD) is the most common cognitive and behavioural
disorder diagnosed among school children. It is characterized by deficient attention and problem
solving, along with hyperactivity and difficulty withholding incorrect responses. This highly prevalent
disorder is estimated to affect 5–10% of children and in many cases, persists into adulthood, leading
to 4% prevalence among adults. Converging evidence from epidemiologic, neuropsychology,
neuroimaging, genetic and treatment studies shows that ADHD is a valid medical disorder.
The majority of studies performed to assess genetic risk factors in ADHD have supported a strong
familial nature of this disorder. Family studies have identified a 2- to 8-fold increase in the risk for
ADHD in parents and siblings of children with ADHD. Various twin and adoption studies have also
highlighted the highly genetic nature of ADHD. In fact the mean heritability of ADHD was shown to
be 0.77, which is comparable to other neuropsychiatric disorders such as schizophrenia or bipolar
disorder.
However, several biological and environmental factors have also been proposed as risk factors for
ADHD, including food additives/diet, lead contamination, cigarette and alcohol exposure, maternal
smoking during pregnancy, and low birth weight. Many recent studies have specifically examined the
relationships between ADHD and these extraneous factors. This review describes some of these
possible risk factors.