ADHD Causes and Risk Factors

ADHD is a complex condition. The exact cause for ADHD is not completely understood; however, a combination of genetic and environmental factors may contribute to the disorder.

Attention-deficit hyperactivity disorder often runs in families. Research has shown that ADHD is hereditary (inherited) and that at least two genes are probably involved in development of the disorder. Several studies involving ADHD in twins confirm this genetic link.

Although ADHD is most likely genetic, several environmental and social factors can affect the development and severity of the disorder. Children born to mothers who used cigarettes and alcohol during pregnancy are at increased risk for attention-deficit hyperactivity disorder.

Young children who are exposed to toxic levels of lead also have a higher risk for developing ADHD. High levels of lead may be present in paint and plumbing in older homes and buildings (e.g., those built prior to 1978).

Food allergies and food sensitivities may increase the risk for attention-deficit hyperactivity disorder. In children with ADHD, eliminating foods the child is sensitive to from the diet can help reduce ADHD symptoms. More research is needed to evaluate the effects of certain foods (e.g., refined sugar, sugar substitutes, food additives) on children who have ADHD.

Brain injuries may increase the risk for ADHD. In some cases, children who have suffered traumatic brain injury (TBI) exhibit symptoms similar to ADHD, such as difficulty concentrating and understanding directions and the inability to control urges.

Areas of the brain that allow us to control impulses, understand the behavior of others, plan ahead, organize, and problem solve are located in the frontal lobes of the cerebrum. The left and right frontal lobes are connected to the cerebellum (area of the brain that coordinates voluntary movements) by complex gray brain matter called basal ganglia (nerve clusters that are involved in routine behaviors).

In studies using imaging tests (e.g., functional magnetic resonance imaging [fMRI], positron emission tomography [PET scan]) to measure brain volume, children with ADHD were shown to have about a 3% reduction in all areas of brain volume compared to children who do not have the disorder. Further results indicated that children who took medication to treat attention-deficit hyperactivity disorder did not experience this reduction in brain volume. More research is needed to further understand the connection between ADHD and brain structure.

Although the relationship is unclear, there are several medical conditions that may accompany ADHD. These conditions include oppositional defiant disorder (ODD), conduct disorder (CD), and Tourette's syndrome.

Oppositional defiant disorder, which occurs in as many as 50% of children with ADHD, causes defiance, stubbornness, and frequent outbursts of temper.

Conduct disorder is a severe anti-social behavior that affects 20–40% of children who have attention-deficit hyperactivity disorder. Children with CD are often aggressive and destructive and are at increased risk for substance abuse. These children frequently get into serious trouble and require immediate treatment.

Tourette's syndrome occurs in a small percentage of children with ADHD. Tourette's is a neurological disorder that causes involuntary tics and repetitive actions, such as blinking, facial twitching, throat clearing, and snorting. Tourette's syndrome usually can be controlled with medication.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 27 Aug 2008

Last Modified: 27 Aug 2015