Attention deficit hyperactivity disorder, or ADHD, affects millions of children and cannot be traced to a single cause. The range of symptoms and severity of the disorder suggest that there are multiple causes of ADHD. Several potential causes of ADHD in children have been suggested over the years, but none of these adequately explains all cases of ADHD.
Genetic Causes of ADHD
ADHD in children has a clear genetic component, although exactly how genetics influence ADHD is unknown. Researchers have found that close relatives of children with ADHD have a 25 percent risk of ADHD themselves. In many cases, parents are diagnosed with ADHD at the same time as their children.
Knowing that genetic causes exist doesn’t mean that those causes can be easily identified. The role of genetics in ADHD onset appears to be very complex: Close relatives of ADHD children have a higher than normal risk of other disorders as well as ADHD, including:
- antisocial disorders
- anxiety disorders
- personality disorders
- substance abuse.
Gender also plays a role in ADHD onset. For unknown reasons, ADHD in children occurs three times as often in boys as in girls, although some researchers suggest that ADHD in girls is under-diagnosed.
ADHD in Children and Parenting
The long-held belief that bad parents are the cause of ADHD in children is simply not true. Poor parenting skills can certainly worsen a child’s ADHD symptoms, but the parenting skills of parents whose children have ADHD are too broad and varied to be considered a cause.
Also, the parents of many ADHD children have other children without ADHD. It seems unlikely that parenting could cause ADHD in some children but not in their siblings.
Brain Injuries and ADHD
A number of brain disorders, biochemical imbalances and neurological conditions have been touted as possible causes of ADHD. The first attempt to explain ADHD in children occurred in the 1960s, when brain injuries were suggested as the cause of ADHD.
While brain injuries can cause symptoms resembling ADHD, only a very small number of children with ADHD have suffered brain damage, so other causes of ADHD are thought to account for the majority of cases.
Brain Scans and Causes of ADHD
Studies of ADHD in children have used brain scans to detect differences in brain activity between ADHD children and control groups of children without ADHD. Brain scan studies have revealed some interesting characteristics of ADHD brain activity:
- ADHD in children is associated with smaller than normal basal ganglia, the nerve clusters that affect how the brain responds to routine behavior.
- ADHD in children not taking ADHD medication is associated with lower than normal white matter levels. White matter is the mass of nerve axons responsible for communication between different parts of the brain.
- Children with ADHD generally have three to four percent less brain volume than control group children.
- Children with ADHD tend to have low levels of frontal lobe activity. The frontal lobe regulates planning, organization, attention levels and impulse control.
- Children with ADHD who are taking ADHD medication have white matter levels similar to control group levels.
- The brains of ADHD children seem to handle neurotransmitters, including dopamine and serotonin, in ways that differ from those of control groups.
While differences in brain structure and activity levels between ADHD children and control group children is intriguing, such studies do not reveal the causes of ADHD, nor do they consistently reveal the same differences between the ADHD brain and the control group brain.
ADHD in Children and Adaptive Behavior
A popular explanation for ADHD in children focuses on adaptive behavior. Many of the symptoms of ADHD in children, such as high activity levels, hyper-vigilance and sensitivity to new sensory information, would be useful adaptive behavior for a hunter-gatherer existence.
Perhaps the causes of ADHD originate in primitive behavioral patterns and survival traits that, like the fight or flight response, were an asset in mankind’s prehistory but are unsuited for the classroom and modern society.
Behavioral Inhibition Defects
One of the leading figures in ADHD research, Russell Barkley, has suggested that the causes of ADHD in children lie in behavior inhibition deficits. Behavior inhibition allows people to delay immediate gratification, to remain focused in spite of distractions and to interrupt one response in favor of another. According to Barkley, ADHD in children results from impaired or defective inhibition defects.
External Causes of ADHD
Although most ADHD researchers tend to view the causes of ADHD as biological factors, several possible external causes of ADHD have been suggested. A potential connection has been found, for instance, between some cases of ADHD in children and smoking or alcohol use by mothers during pregnancy.
High levels of lead in the body may increase the risk of ADHD in children, according to some studies. However, like the theory that alcohol use during pregnancy causes ADHD, lead levels cannot explain all cases of ADHD in children.
Diets, particularly diets including food additives and sugar, are often suggested as causes of ADHD. Dietary changes have improved symptoms in approximately 5 percent of cases of ADHD in children, but the majority of those children were also found to have food allergies.
Other suggested causes of ADHD in children have included:
- bad parenting
- disruptive family life
- drug use
- low socioeconomic status
- poor skills
- video games.
While any of these factors can worsen symptoms of ADHD in children, none of these are considered causes of ADHD.
EMedicine Health (2005). Attention deficit hyperactivity disorder. Retrieved August 2, 2007, from the EMedicine Health Web site: http://www.emedicinehealth.com/attention_deficit_hyperactivity_disorder/article_em.htm.
Mental Health Channel (2007). Attention deficit hyperactivity disorder (ADHD). Retrieved August 2, 2007, from the Mental Health Channel Web site: http://www.mentalhealthchannel.net/adhd/.
National Institute of Mental Health (2007). Attention deficit hyperactivity disorder [NIH Publication No. 03-3572]. Retrieved August 2, 2007, from the NIMH Web site: http://www.nimh.nih.gov/healthinformation/adhdmenu.cfm.