What Causes Attention Deficit Hyperactivity Disorder?

There are many theories about the causes of attention deficit hyperactivity disorder, or ADHD. Experts speculate on a wide range of probable causes - genetics, environmental pollutants, food allergies and challenging home environments.

In his new book, "What Causes ADHD? Understanding What Goes Wrong and Why," Michigan State University psychologist Joel Nigg brings together the most recent neuropsychological research in an attempt to answer this challenging question.

"Essentially there are multiple causes," said Nigg. "Some we already know of, others have been suggested and disproved, still others deserve more study."

The disorder is defined as a problem with inattentiveness, over activity, impulsivity or a combination of those. While children in general are much more active than adults and less patient with various tasks, children diagnosed with ADHD are out of the normal range for their age and development, and cause impairment in the child's life. In the United States, as many as 7 million children have been diagnosed with ADHD.

"If you're a professional, how do you answer questions from parents, many of whom know very little about scientific findings related to ADHD?" Nigg asked. "Hopefully this book can bring a broad range of data within easy reach of professionals who find it difficult to keep up with such huge literatures."

Nigg is a clinical psychologist who has worked with hundreds of children with ADHD and related conditions. He has trained numerous graduate students in the evaluation and assessment of ADHD in children, adolescents and adults. He also is an active scientist engaged in research on the condition.

His research has focused on neuropsychological markers of ADHD, genetics of ADHD, family processes, and, most recently, the potential ADHD-causing effects of environmental pollutants, including lead, cadmium and persistent organic pollutants such as PCBs.

"There are so many things written about ADHD that are simplistic and brief, often because they are for a different purpose," he said. "I wanted to explain it with more detail and get everything in one place."