The exact causes of adult attention deficit hyperactivity disorder (ADHD) are unknown. What we do know is that are a lot of possible reasons a person develops attention deficit disorder, and the factors vary from person to person. Today, there is no medical laboratory or blood test for this disorder, but scientific behavioral assessment measures have been used and proven by research for decades.
Someday, our understanding of the causes of ADHD may lead to more effective therapies. Recent research evidence is growing regarding the importance of genes and heritability significantly contributing to a person’s chances of an eventual diagnosis of this disorder.
Genes & ADHD
ADHD has a strong genetic basis in the majority of cases, as a person with ADHD is four times as likely to have a relative who was also diagnosed with attention deficit disorder. At the moment, researchers are investigating many different genes, particularly ones involved with the brain chemical dopamine. People with ADHD seem to have lower levels of dopamine in the brain.
Adults with ADHD who carry a particular version of a certain gene have thinner brain tissue in the areas of the brain associated with attention. Research into this gene has showed that the differences are not permanent, however. As adults with ADHD age, their brains continue to develop to a normal level of thickness, resulting in many ADHD symptoms subsiding.
ADHD’s Connection to Nutrition & Food
Certain components of the diet, including food additives and sugar, can have clear effects on behavior. Some experts believe that food additives may exacerbate ADHD. And a popular belief is that refined sugar may be to blame for a range of abnormal behaviors.
However, the belief that sugar is one of the primary causes of attention deficit disorder does not have strong support in the research data. While some older studies did suggest a link, more recent research does not show a link between ADHD and sugar. While the jury is still out on whether sugar can contribute to ADHD symptoms, most experts now believe that the link simply does not exist — and if it does, it is not a strong one. Simply removing sugar from a child’s diet is unlikely to significantly impact their ADHD behavior.
Some studies also suggest that a lack of omega-3 fatty acids is linked to ADHD symptoms. These fats are important for brain development and function, and there is plenty of evidence suggesting that a deficiency may contribute to developmental disorders including ADHD. Fish oil supplements appear to alleviate ADHD symptoms, at least in some children, and may even boost their performance at school.
The Environment, Brain Injury, and ADHD
There may be a link between ADHD and a mother smoking while pregnant. However, women who suffer from ADHD themselves are more likely to smoke, so a genetic explanation cannot be ruled out. Nevertheless, nicotine can cause hypoxia (lack of oxygen) in utero.
Lead exposure has also been suggested as a contributor to ADHD. Although paint no longer contains lead, it is possible that preschool children who live in older buildings may be exposed to toxic levels of lead from old paint or plumbing that has not been replaced.
Brain injury may also be a cause of attention deficit disorder in a very small minority of children. This can come about following exposure to toxins or physical injury, either before or after birth. Experts say that head injuries can cause ADHD-like symptoms in previously unaffected people, perhaps due to frontal lobe damage.
ADHD researchers are currently investigating the frontal lobes of the brain — the areas controlling problem-solving, planning, understanding other people’s behavior, and restraining our impulses.
The brain is divided into two halves, and the two frontal lobes communicate through a bundle of nerve fibers called the corpus callosum. These areas, and nearby brain cells, are being examined by ADHD researchers. Using brain imaging methods, the experts can get an idea of the location of the psychological deficits of ADHD.
A 2002 study found that children with ADHD had 3-4 percent smaller brain volumes in all the brain regions measured. But children on ADHD medication had similar brain volumes to unaffected children, in some of the areas measured.
One big difference was the amount of “white matter” — long-distance connections between brain regions that normally become stronger as a child grows up. Children with ADHD who had never taken medication had an abnormally small volume of white matter.