What causes ADHD (ADD)?

My professional web page is located at: http://www.relatedminds.com
I'm often asked "What causes ADHD?" and thought today's blog might just address that.

How many people have ADHD? Isn't it over diagnosed?
ADHD occurs in approximately 3-7 percent of the childhood population. Studies find that approximately 2-5 percent of the adult population have ADHD. Boys more likely to have the disorder than girls by 3:1. Among adults, the gender ration falls to 2:1 or lower. The reason for that seems to be that girls don't exhibits some aspects of ADHD that boys do, such as hyperactivity, but later do show signs of inattention. 

ADHD has been found to exist in virtually every country in which it has been investigated, including North America, South America, Great Britain, Scandinavia, Europe, Japan, China, Turkey and the middle East. It is NOT something made up by Western doctors, as some would tell you. The disorder may not be referred to as ADHD in these countries, and may not be medically treated as in North America. Still  there is little doubt that the disorder is universal among human populations everywhere. 

One of the things we have found is that ADHD is more likely to be found in families in which others have the disorder or where depression is more common. Dr. Russell Barkley (most of the information provided here can be found in his writing, and I highly recommend his website) has found that ADHD is also more likely to occur in those with conduct problems and delinquency, tic disorders or Tourette’s Syndrome, learning disabilities, or those with a history of prenatal alcohol or tobacco-smoke exposure, premature delivery or significantly low birth weight, or significant trauma to the frontal regions of the brain.  Almost 50% of individuals with ADHD also have another comorbid disorder. This is why, especially with children, you should consider getting a more comprehensive assessment than often given in a medical doctors office, as learning disabilities and other comorbid conditions need to be ruled out.

What causes ADHD?
Scientific evidence is overwhelming that ADHD "has very strong biological contributions to its occurrence." What those are have not yet been identified, but there is little question that heredity/genetics makes the largest contribution to the expression of the disorder in the population.  How big of an influence does genetics have on ADHD? Approximately 80 percent, meaning that genetic factors account for 80 percent of the differences among individuals in this set of behavioral traits. This is about the same as for how tall you are, or how smart you are. Several genes associated with the disorder have been already been identified. There are some situations where heredity does not seem to be a factor.  These include "difficulties during pregnancy, prenatal exposure to alcohol and tobacco smoke, prematurity of delivery and significantly low birth weight, high body lead levels, as well as post-natal injury to the prefrontal regions of the brain have all been found to contribute to the risk for ADHD." But these are usually the exceptions. For the most part, the vast majority of ADHD seems directly related to genetics.

Dr. Barkley points out, "Research has not supported popularly held views that ADHD arises from excessive sugar intake, food additives, excessive viewing of television, or poor child management by parents."  Full moons and sugar highs seem to affect the parents and teachers more than the children. Therefore, most medical interventions are not aimed at these disproven theories, which remain popular because they have quick miracle cures attached to them...which do not work.

I hope the brief and basic outline is helpful.