Causes of ADD / ADHD

No single cause seems to apply to everyone with ADHD (ADD). Viruses, harmful chemicals in the environment, genetics, problems during pregnancy or delivery, or anything that impairs brain development can play a role in causing the attention problems in ADHD.

Exploring the following possibilities and their associated online references can help you better understand the complexity of ADHD risk factors and causes

Brain structures and activity as a cause of ADD / ADHD

Studies of people with ADHD show that certain brain areas have less activity and blood flow and that certain brain structures are slightly smaller. These differences in brain activity and structure are mainly evident in the prefrontal cortex, the basal ganglia, and the cerebellum. These areas help to inhibit behavior, sustain attention, and control mood. (Source: NICHCY)

NIMH scientists have demonstrated a link between a person's ability to pay continued attention and the level of activity in the brain. Adult subjects were asked to learn a list of words. As they did, scientists used a PET (positron emission tomography) scanner to observe the brain at work. The researchers measured the level of glucose used by the areas of the brain that inhibit impulses and control attention. Glucose is the brain's main source of energy, so measuring how much is used is a good indicator of the brain's activity level. The investigators found important differences between people who have ADHD and those who don't. In people with ADHD, the brain areas that control attention used less glucose, indicating that these areas were less active. It appears from this research that a lower level of activity in some parts of the brain may cause inattention. (Source: NIMH)

Brain chemistry as a cause of ADD / ADHD

Strong evidence suggests that certain chemicals in the brain -- called neurotransmitters -- play a large role in ADHD-type behaviors. Neurotransmitters help brain cells to communicate with each other. The neurotransmitter that seems to be most involved with ADHD is called dopamine. Dopamine is widely used throughout the brain. When neurotransmitters don't work the way they are supposed to, brain systems function inefficiently, and problems result. With ADHD, these problems are inattention, hyperactivity, impulsivity, and related behaviors. (Source: NICHCY)

Genetic factors as a cause of ADD / ADHD

Research shows that ADHD tends to run in families, so a genetic component for ADHD is likely. Children who have ADHD usually have at least one close relative who also has ADHD. At least one-third of all fathers who had ADHD in their youth bear children who have ADHD. The majority of identical twins share the ADHD trait. (Source: NIMH)

In London, the ADHD Genetic Group "identifies the genes involved in ADHD and related behavioural traits, and investigates how such genes work together and with environment to influence behaviour."

Problems surrounding pregnancy and toxins as a cause of ADD / ADHD

Throughout pregnancy and continuing into the first year of life, the brain is constantly developing. It begins its growth from a few all-purpose cells and evolves into a complex orgn made of billions of specialized, interconnected nerve cells. By studying brain development in animals and humans, scientists are gaining a better understanding of how the brain works when the nerve cells are connected correctly or incorrectly. Scientists at NIMH and other research institutions are tracking clues to determine what might prevent nerve cells from forming the proper connections. Some of the factors they are studying include drug use during pregnancy, toxins, and genetics.

Research shows that a mother's use of cigarettes, alcohol, or other drugs during pregnancy may have damaging effects on the unborn child. These substances may be dangerous to the fetus' developing brain. It appears that alcohol and the nicotine in cigarettes may distort developing nerve cells. For example, heavy alcohol use during pregnancy has been linked to fetal alcohol syndrome (FAS), a condition that can lead to low birth weight, intellectual impairment, and certain physical defects. Many children born with FAS show much the same hyperactivity, inattention, and impulsivity as children with ADHD.

Drugs such as cocaine—including the smokable form known as crack—seem to affect the normal development of brain receptors. These brain cell parts help to transmit incoming signals from our skin, eyes, and ears, and help control our responses to the environment. Current research suggests that drug abuse may harm these receptors. Some scientists believe that such damage may lead to ADHD.

Toxins in the environment may also disrupt brain development or brain processes, which may lead to ADHD. Lead is one such possible toxin. It is found in dust, soil, and flaking paint in areas where leaded gasoline and paint were once used. It is also present in some water pipes. Some animal studies suggest that children exposed to lead may develop symptoms associated with ADHD, but only a few human cases have actually been found.

Other risk factors for ADHD

Some tantalizing studies hint at other risk factors for ADHD:

1. Too much television - Does too much television viewing train the brain to require constant stimulation, so that the real world is boring in comparison?   A recent research study (Source: LDA) looked at the connection between the amount of television that very young children watched and attention problems years later when those children were in school. The researcher found that for each additional hour of television per day that children watched on average before age three, they were 10 percent more likely to have attention problems, by parents' reports. A question to consider:
2. Lack of a loving and secure environment - Children who grow up in environments where their bonding and attachment needs are not met are at an increased risk for developing symptoms which closely parallel the symptoms of ADHD.
3. Poor nutrition – Dietary deficiencies can cause behavioral problems and can exacerbate ADHD. In addition, some studies indicate that poor nutrition may be a risk factor for ADHD. Food additives; food allergies; infant malnutrition; insufficient omega-3 fatty acids; or other dietary problems may contribute to or possibly cause ADHD or ADD. More research will help us to understand the role of diet relative to ADHD.

Related links for Causes and Risk factors of ADD / ADHD

Other Related Links

Attention Deficit Hyperactivity Disorder (PDF) – A comprehensive 30-page booklet. Scroll to What Causes ADHD?. (National Institute of Mental Health (NIMH))

Attention Deficit/Hyperactivity Disorder – A comprehensive Briefing Paper "written to help parents, teachers, and others interested in AD/HD know what to look for, what to do, and how to get help.” Scroll down to What Causes ADHD?. (National Dissemination Center for Children with Disabilities (NICHCY))

What Causes Attention-Deficit Hyperactivity Disorder? – Comprehensive article addresses biologic factors, genetic factors, problems surrounding pregnancy, and dietary factors. (University of Maryland Medical Center (UMMC))

The ADHD Genetic Group – "Investigates how genes involved with ADHD work together and with environment to influence behaviour." (Kings College, London)

Nutrition and Dietary Supplements – Addresses the effects of dietary restrictions and supplements on ADHD. (University of Maryland Medical Center (UMMC))

ADHD and Diet (commercial site) – A personal account of how different foods affect this author’s child, with recommendations. Brief review of studies on whether diet can cause ADHD. (Aspen Education Group)

What's the Connection Between Television and Attention Problems? – How television watching might affect developing young minds. (Learning Disabilities Association of America (LDAA))

Jaelline Jaffe, Ph.D., Tina de Benedictis, Ph.D., and Robert Segal, M.A. contributed to this article. Last modified on: 9/17/07.