By Jennifer Copley (Last Updated 27 May 2008)
Attention-Deficit Hyperactivity Disorder (ADHD) is a genetic neurobiological condition. Although environmental factors such as stressors in the child’s home or school life can exacerbate the disorder, they do not cause it.
There are a number of theories about the specific physiological causes of ADHD that have been supported by scientific research. These include genetics, ingestion of toxic substances, brain injury or abnormality, and sensitivity to certain food additives.
While about 5% of the general population is estimated to have ADHD, 25% of close relatives of children diagnosed with ADHD also have the condition. Twin studies have confirmed the genetic link, and specific genes have been identified that are associated with the disorder.
Studies indicate a potential correlation between drinking alcohol and smoking cigarettes while pregnant and ADHD in children. In addition to absorbing such toxic substances in utero, children may also be exposed to lead when they are young through paint in old buildings (newer paints do not contain lead). Lead exposure in childhood has also been linked with ADHD.
Brain Injury or Abnormality
While the majority of children with ADHD have not suffered brain injuries, certain types of brain injury can induce ADHD symptoms. Also, a study that compared the brains of ADHD children with those of ordinary children using MRI scans found slight differences in several areas, indicating that the disorder is brain-based.
Sugar and Food Additives
Approximately 5% of children with ADHD respond positively to diet restrictions of sugar and food additives. However, studies in which parents and children were not told whether the children were given sugar or a sugar substitute have indicated that sugar has little, if any, effect on ADHD symptoms for most children.
People may perceive more ADHD symptoms after children consume sugar because they expect sugar to worsen the condition. However, parents who believe that their children have been given sugar (when they have actually been given a substitute) are just as likely to say that ADHD symptoms have worsened as parents of children who are given actual sugar. This suggests that improvements as a result of dietary restrictions occur because:
- it is food additives that are the problem rather than sugar, or
- sugar reduction does reduce ADHD symptoms but this effect is psychosomatic, or
- a small percentage of children are particularly sugar-sensitive.
Reducing sugar in the diet brings a variety of other health benefits, so even if it does not help with ADHD, it is certainly a worthwhile endeavour.
The link between food additives and ADHD has more scientific support. McCann et al.’s 2007 study of the effects of food additives on children found that both sodium benzoate-based preservatives and artificial colours, commonly found in children’s snack foods and sodas, significantly increased hyperactivity.
The important thing to remember is that ADHD is not caused by psychological stress, though it can be made worse by stress. While the child cannot help behaving the way he or she does without intervention (ideally, a combination of medication and behavioural therapy), the condition is highly treatable, and there are many effective strategies for improving behaviour, organizational skills, and interpersonal interactions.
For more information about ADHD, including symptoms and treatments, see the main ADHD page.
- Canadian ADHD Resource Alliance. (n.d.). “What is Attention Deficit Hyperactivity Disorder.” Caddra.ca.
- Centers for Disease Control and Prevention, Department of Health and Human Services. (2005). “Symptoms of ADHD.” Cdc.gov.
- McCann, D., Barrett, A., Cooper, A., Crumpler, D., Dalen, L., Grimshaw, K., Kitchin, E., Lok, K., Porteous, L., Prince, E., Sonuga-Barke, E., Warner, J.O., & Stevenson, J. (2008). “Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial.” TheLancet.com.
- National Institutes of Mental Health, U.S. Department of Health and Human Services. (2008). “Attention Deficit Hyperactivity Disorder.” Nimh.Nih.gov.
- Silver, L., MD. (2007). “Diagnosing Related Conditions in ADHD Children and Adults.” ADDITUDE: Living Well with ADHD and Learning Disabilities. Additudemag.com.