Causes and Risk Factors of Attention-Deficit Hyperactivity Disorder (ADHD)

Attention-deficit hyperactivity disorder (ADHD) is a common neurobehavioral condition that causes symptoms of inattention, hyperactivity, and impulsivity. It is usually diagnosed during childhood, but it can also affect adults.

The exact cause of ADHD isn't known. But researchers suspect there may be several factors that determine whether someone might develop ADHD. Genetics, toxins, exposure to substances during prenatal development, and certain medical conditions can all play a role.

This article explores the different causes of attention-deficit hyperactivity disorder.

Common Causes of ADHD

Researchers believe that there are many different causes of ADHD. Some of the factors that can contribute or increase the risk of developing ADHD include:

• Genetics
• Exposure to environmental toxins
• Exposure to substances in utero
• Illness and injury
• Premature birth
  

Genetics

Whether you have recently been diagnosed with ADHD or have been living with ADHD for many years, a question almost all adults ask is: "Will my children have ADHD, too?" The answer is: It depends.

ADHD is primarily a hereditary disorder. It is estimated that the percentage of genetic contribution to ADHD is over 70%.

Despite this strong genetic link, having ADHD doesn’t automatically mean you'll pass it on to your child. This is because it is a combination of genes and environmental factors that determine whether a child develops ADHD.

Children can inherit ADHD genes without them being activated. For example, one research study found that only one-third of fathers with ADHD had children that also developed ADHD.

To date, several gene candidates have been found in families who demonstrate ADHD. However, scientists feel that it is not one particular gene but the interaction of several of these genes and the environment that cause ADHD symptoms to manifest.

ADHD is not a sex-linked condition. In other words, ADHD does not occur only in males and is thus not passed down only from a father to the children. Some people think, “It’s only fathers who can have ADHD, and if the dad doesn’t have ADHD then the child can’t possibly have it.” This is inaccurate.

Illnesses and Injuries

Illnesses such as meningitis or encephalitis can result in learning and attention problems.

A small percentage of people experience ADHD symptoms as a result of brain damage, such as an early brain injury, trauma, or another impediment to normal brain development.

One study published in JAMA Pediatrics found that children with a history of traumatic brain injuries, even if less severe, have an increased risk of developing ADHD for as long as 10 years after the injury.

Toxins

Being exposed to certain environmental toxins during childhood can increase the risk that a child will develop ADHD.

Exposure to lead (even low levels) can result in hyperactivity and inattention. Lead can be found a variety of places, such as in the paint of homes built before 1978 or previously in gasoline.

Exposure to Substances in Utero

A gestational parent's health and habits during pregnancy can also play a role in the development of ADHD. Poor nutrition and infections during pregnancy can increase the risk of ADHD, for example.

There's also evidence that using some substances during pregnancy increases the risk that the child will develop ADHD.

Smoking 

A 2018 study published in Pediatrics found a significant relationship between smoking during pregnancy and the likelihood of a child having ADHD. The risk of ADHD was greater in children whose mothers smoked heavily. The study couldn't conclude that smoking causes ADHD, but it did indicate that a correlation exists.

Alcohol

Some studies have found that parents who drink during pregnancy are more likely to have children with ADHD. A 2018 study found that consuming four or more drinks at a time, or regular low to moderate alcohol, use was associated with a significant increase in the chances that a child would later have ADHD.

A 2017 study, however, found that there was no link between maternal alcohol use and a clinical ADHD diagnosis in children. This study suggested that children may develop some symptoms of ADHD if their parent used alcohol during pregnancy, but they didn't necessarily qualify for an ADHD diagnosis.

Summary

It's likely that ADHD stems from a variety of causes. Someone who has a genetic predisposition, for example, may encounter environmental factors that also contribute to the development of ADHD. Toxins, exposure to substances during prenatal development, certain types of infections, and brain injuries can increase the risk that a person will develop ADHD.

A Word From Verywell

Researchers continue to learn more about the potential causes and risk factors for ADHD. While the exact causes may not be known, it is important to know that there are effective treatments available that can help you or your child manage the symptoms of the condition. Talk to your healthcare provider if you think you or your child may have ADHD to learn more about what treatment options might work best for you.