Environmental risk factors for attention-deficit hyperactivity disorder
Version of Record online: 20 AUG 2007
©2007 The Author(s)/Journal Compilation © 2007 Foundation Acta Pædiatrica/Acta Pædiatrica
Volume 96, Issue 9, pages 1269–1274, September 2007
How to Cite
Banerjee, T. D., Middleton, F. and Faraone, S. V. (2007), Environmental risk factors for attention-deficit hyperactivity disorder. Acta Paediatrica, 96: 1269–1274. doi: 10.1111/j.1651-2227.2007.00430.x
- Issue online: 20 AUG 2007
- Version of Record online: 20 AUG 2007
- Received 13 March 2007; revised 5 June 2007; accepted 15 June 2007.
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.
Conclusion: Although a substantial fraction of the aetiology of ADHD is due to genes, the studies reviewed in this article show that many environmental risk factors and potential gene–environment interactions also increase the risk for the disorder.