ADHD, like many syndromes, is felt to be caused by a combination of genetic and environmental factors. ADHD certainly runs in families. Estimates are that 70 to 80 percent of the incidence of ADHD is genetically related. Indeed, it is unusual for me to see a child with ADHD who does not have a parent or close relative who has ADHD, whether diagnosed or not. There are many different genes that have been associated with ADHD, with no specific gene having a strong association. This makes it unlikely that any particular genetic therapy will have a significant effect, at least in the near future.
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There are a number of environmental factors from pregnancy onward that can cause the development of ADHD as well. Brain injury at any time before or after birth, prematurity, low birth weight and alcohol or tobacco use during pregnancy all have been associated with an increased incidence of ADHD.
Many influences that occur after birth are associated with increased rates of ADHD. These include birth trauma, seizures in the newborn and any type of brain injury. Exposure to environmental toxins through childhood also plays a significant role. In one study of 1,139 children between 8 and 15 years old, those with higher levels of pesticides in their blood were more than twice as likely to have ADHD. In another study, it was shown that eating organic fruits and vegetables decreased pesticide levels by 80 percent. High lead levels are also associated with ADHD. Even psychological stress, child abuse and parenting issues can increase the probability of a child presenting symptoms of ADHD. In fact, it can be difficult to differentiate between symptoms of ADHD and PTSD, which is also caused by a number of stressful childhood exposures.
How Does ADHD Affect the Brain?
How does ADHD affect brain function? People with ADHD have abnormalities in the function of a number of regions of the brain and the connections between brain regions. Probably most important is the frontal lobe. This is the part of the brain responsible for “executive function,” essentially the “boss” of the brain. It is the part of the brain involved in planning and following through. It is also responsible for “inhibitory control” which allows us to stop and think for a second before acting impulsively. Studies have shown that the frontal lobes of children with ADHD develop more slowly than those of non-ADHD children, although they do seem to catch up eventually.
Certain neurotransmitters, which are crucial for nerve cells communicating with each other, seem to be affected by ADHD. The best studied are dopamine and norepinephrine. The function of these two neurotransmitters appears to be impaired in many people with ADHD. In fact, as we will discuss later, the most common ADHD medications seem to work by increasing the available amount of dopamine and norepinephrine. This is where the idea that ADHD is simply a “chemical imbalance” is derived. However, it is important to remember that neurotransmitter levels are not fixed, but variable. Not just medication, but diet, exercise, social success and many psychological factors can have significant effects on neurotransmitter levels.
Prevention of ADHD is not easy. Certainly avoiding pregnancy and birth complications, decreasing exposure to pesticides and heavy metals and lessening psychological stress on infants and young children are all to be desired. However, most cases of ADHD do not have these risk factors, except perhaps for the fact that the vast majority of children are exposed to food-borne pesticides.
More importantly, there are a number of non-medication interventions that modify the symptoms of ADHD in those who have the condition. Sometimes these interventions can have dramatic results; other times changes are modest but significant. These will be discussed further in following sections.