This is an exciting time in ADHD research. The expansion of knowledge in genetics, brain imaging, and behavioral research is leading to a better understanding of the causes of the disorder, how to prevent it, and how to develop more effective treatments for all age groups.
The US National Institute of Mental Health has studied ADHD treatments for school-aged children in a large-scale, long-term study called the Multimodal Treatment Study of Children with ADHD (MTA study). It also funded the Preschoolers with ADHD Treatment Study (PATS), which involved more than 300 preschoolers who had been diagnosed with ADHD. The study found that low doses of the stimulant methylphenidate are safe and effective for preschoolers, but the children are more sensitive to the side effects of the medication, including slower than average growth rates.18 Therefore, preschoolers should be closely monitored while taking ADHD medications.19,20
PATS is also looking at the genes of the preschoolers, to see if specific genes affected how the children responded to methylphenidate. Future results may help scientists link variations in genes to differences in how people respond to ADHD medications. For now, the study provides valuable insights into ADHD.21
Scientists are not sure what causes ADHD, although many studies suggest that genes play a large role. Like many other behavioral health illnesses, ADHD probably results from a combination of factors. In addition to genetics, researchers are looking at possible environmental factors, and are studying how brain injuries, nutrition, and the social environment might contribute to ADHD.
Inherited from our parents, genes are the "blueprints" for who we are. Results from several international studies of twins show that ADHD often runs in families. Researchers are looking at several genes that may make people more likely to develop the disorder.2,3 Knowing the genes involved may one day help researchers prevent the disorder before symptoms develop. Learning about specific genes could also lead to better treatments.
Children with ADHD who carry a particular version of a certain gene have thinner brain tissue in the areas of the brain associated with attention. This NIMH research showed that the difference was not permanent, however, and as children with this gene grew up, the brain developed to a normal level of thickness. Their ADHD symptoms also improved.4
Studies suggest a potential link between cigarette smoking and alcohol use during pregnancy and ADHD in children.5,6 In addition, preschoolers who are exposed to high levels of lead, which can sometimes be found in plumbing fixtures or paint in old buildings, may have a higher risk of developing ADHD.7
Children who have suffered a brain injury may show some behaviors similar to those of ADHD. However, only a small percentage of children with ADHD have suffered a traumatic brain injury.
The idea that refined sugar causes ADHD or makes symptoms worse is popular, but more research diskounts this theory than supports it. In one study, researchers gave children foods containing either sugar or a sugar substitute every other day. The children who received sugar showed no different behavior or learning capabilities than those who received the sugar substitute.8 Another study in which children were given higher than average amounts of sugar or sugar substitutes showed similar results.9
In another study, children who were considered sugar-sensitive by their mothers were given the sugar substitute aspartame, also known as Nutrasweet. Although all the children got aspartame, half their mothers were told their children were given sugar, and the other half were told their children were given aspartame. The mothers who thought their children had gotten sugar rated them as more hyperactive than the other children and were more critical of their behavior, compared to mothers who thought their children received aspartame.10
Recent British research indicates a possible link between consumption of certain food additives like artificial colors or preservatives, and an increase in activity.11 Research is under way to confirm the findings and to learn more about how food additives may affect hyperactivity.