Research has not determined what exactly causes ADHD, but scientists believe it could be in imbalance in neurotransmitters, the chemicals that regulate how the brain processes and regulates responses to stimuli. Also, a landmark 1996 study conducted at the National Institutes for Mental Health (NIMH) also found that two portions of the brain thought to regulate attention are smaller in children with ADHD. Since then, brain imaging technology has advanced and many other studies have shown disparities between the brains of children with and without ADHD, including one 2007 study that showed that the brains of children with ADHD mature in the same pattern as those of other children, but up to three years later.  Scientists are still working to discover just what these differences mean.

Why does one child’s brain have trouble regulating attention and activity levels, while another’s doesn’t? There doesn’t seem to be one overwhelming reason, but there are a number of factors that can make a child more likely to develop ADHD.

Heredity

Like many mental conditions, along with other traits ranging from diabetes to alcoholism to red hair, ADHD seems to run in families. However, since the disorder (called minimal brain dysfunction or hyperactivity in previous decades) may have gone undiagnosed, parents will have to look for clues on their family tree. School failures, delinquency, multiple divorces, employment problems and addictions can all be signs that family members may have had undiagnosed and untreated ADHD.

Smoking, drinking and drug use during pregnancy

Several studies link each of these damaging behaviors with children later developing ADHD. Smoking and drinking are linked to prematurity, another factor in ADHD, but researchers are discovering other links. For example, a 2009 British study found that smoking disrupted the thyroid function of both mother and fetus, which they theorized could lead to chemical imbalances in the infant brain. Smoking can also reduce oxygen flow to the embryo’s brain.

Prematurity
Infants born prematurely are more likely to develop ADHD as children. In 2006, Danish researchers found babies born between 34 and 36 weeks were 70 percent more likely to develop the condition later. The “why” of prematurity and ADHD is still a mystery, but theories include lack of oxygen and damage to the brain.

Lead

Preschoolers exposed to high levels of lead are more likely to develop ADHD. The brain develops at a breakneck pace during a child’s first three years, and lead is thought to disrupt enzymes needed to build the “roadways” of synapses and neurons that process information.

Nutritional Triggers

The idea that sugar makes kids hyper is probably a myth. Medical evidence has found no strong link between sweets and ADHD. However, recent research has indicated that some other food additives, like artificial colors and preservatives, as well as pthalates (chemicals found in some plastics) may contribute to hyperactivity.