Top 10 Theories: What Causes ADHD?

Theories abound when it comes to the causes of ADHD. But which ones have been proven true?

Though we don’t completely understand why some children are more susceptible to ADHD than others, the brain changes that are seen in children with ADHD symptoms are not theoretical. Studies show that regions of the brain affected by ADHD are the same regions that control attention as well as impulse control in children without ADHD. Here are 10 theories — some more plausible than others — to explain the brain changes that cause ADHD symptoms:

1. Genetics. ADHD symptoms tend to run in families. Studies show that one in four children with a diagnosis of ADHD will have a close family member with ADHD.
2. Lead exposure. Studies have shown an association between lead exposure and ADHD symptoms in young children. Lead may enter a child's drinking water from old plumbing fixtures. Children may also be exposed from lead paint. "These exposures are known to increase the risk of ADHD, but these exposures are becoming increasingly rare and most children with a diagnosis of ADHD have no evidence of significant lead exposure," Hunter notes.
3. Cigarettes and alcohol. Two toxins that have been shown to increase the risk of ADHD in children are cigarette smoke and alcohol. Smoking and drinking during pregnancy are associated with a number of serious health risks for both mother and fetus. Not surprisingly, several studies have specifically linked these substances to an increased risk of having a child with ADHD.
4. Medications taken during pregnancy. A study done in the Netherlands found that children of women who were treated for high blood pressure during pregnancy with a medication called labetalol (Normodyne, Trandate) had a significantly higher risk of ADHD. "It may be that some medications given to a mother may interfere with fetal oxygen, but these are isolated findings and require more research," cautions Hunter.
5. Fluoride. The theory that fluoride could cause ADHD arose from a study done in rats. Although rats exposed to fluoride during the study did develop ADHD symptoms, this may not necessarily translate into increased risk among humans. "I know of no convincing evidence that fluoride is a significant ADHD risk factor for children," says Dribinsky.
6. Sugar and sugar substitutes. Both refined sugar and sugar substitutes have been studied as possible ADHD causes. Most studies show that neither sugar nor sugar substitutes affect children's behavior or their learning ability. According to the National Institute of Mental Health (NIMH), there is actually more research to suggest that sugar is not linked to ADHD symptoms than there is research to support an association between the two.
7. Celiac disease and food allergies. Some research supports the theory that food intolerance or food allergies, such as in the intolerance to the protein gluten seen in celiac disease, may be a trigger for ADHD symptoms. Studies have shown that a small percentage of children may get some relief from ADHD symptoms with diet restrictions. "Food sensitivities and nutritional deficiencies may play a role, but more research needs to be done," says Dribinsky.
8. Food additives. It has long been suspected that food additives such as food coloring or food preservatives might cause ADHD symptoms or make them worse. Recent research published in Britain supports a link between these additives and an increase in ADHD symptoms. Research is under way to see if these findings can be confirmed. "The effects of food additives are probably negligible for most children with ADHD, but some children may be more sensitive than others," Hunter explains.
9. Pesticides. "Recent studies done at Harvard suggest that pesticide exposure may increase the risk of ADHD in children," notes Hunter. The researchers found that children who had high levels of pesticide in their urine had almost double the risk of ADHD as children who had undetectable levels.
10. Complications during pregnancy. Many studies show that a difficult pregnancy can lead to ADHD. These may be complications that occur during fetal development in the womb, or complications that affect the baby's brain during delivery. Complications that have been identified include high blood pressure during pregnancy, bleeding before the birth of the baby, babies who remain in the womb beyond their due date, long delivery time, and anything that impacts the baby’s oxygen supply during birth.

It remains unclear which of these theories play the biggest role in ADHD symptoms. It’s likely that a number of factors work together to determine whether a child develops ADHD. As Dribinsky points out, "We know that children with ADHD have brains that function differently … What we need to know more about is how the environment triggers ADHD symptoms."

Adds Hunter: "Children who have a genetic predisposition for ADHD may be more vulnerable to pesticides, toxins, or other triggers. The areas of the brain that are responsible for attention and activity regulation are very sensitive."

While exact ADHD causes are not yet known, this is an exciting and active time for research and discovery in ADHD. Some earlier theories seem less promising now, but new theories may hold the key to unraveling the mystery of ADHD in the future.