Studies report that 75 to 90 percent of the risk of ADHD can be traced to our genes.
There are currently estimated to be about 7,000 different genes associated with susceptibility to ADHD, each of which slightly increases your risk. It's not that people with ADHD will have all 7,000 genes; different people have different combinations and amounts of these genes. The number of many is average, the number of few is large, and the number of few is small.
If you get a certain amount of these factors plus a certain amount of environmental risk, that puts you over the threshold of developing ADHD.
Scientists are still trying to determine how genes increase ADHD risk and how the environment of a susceptible child, teen, or adult triggers ADHD symptoms such as hyperactivity, impulsivity, and/or inattention and inattention. It's important for parents of hyperactive children to understand that they shouldn't blame themselves. The causes of ADHD are extremely complex. Most environmental risks, such as genetic risks, are small and gradual.
Genes and ADHD
The risk of ADHD runs in families. A recent Norwegian study² of 2.4 million people showed that 17% to 24% of children whose parent had ADHD also had ADHD. When both parents have ADHD , 33% of the children will also have ADHD.
Inherited genetic risk manifests itself in other ways as well. Siblings of children with ADHD have a 26 to 42 percent risk of having ADHD.
How ADHD affects the brain
How genes increase risk is unclear. But the researchers do know that many of the genes they discovered play a role in the brain. Some help regulate brain chemicals called neurotransmitters, such as norepinephrine and dopamine, which are involved in thinking, attention, learning and motivation.
Low levels of the neurotransmitter dopamine is a hallmark of ADHD and is associated with ADHD symptoms such as difficulty concentrating and mood swings. A 2022 study found that differences in the way genes control neurotransmitters are located in the brain's caudate nucleus and frontal cortex regions—areas involved in controlling attention.
Genes may be involved in other key differences found in the brains of people with ADHD. These include smaller areas involved in attention, including the prefrontal cortex and basal ganglia, as well as the cerebellum, which regulates movement.
Environmental and other causes of ADHD
Experts believe that for people who are at higher genetic risk for ADHD, the environment around birth and during childhood may trigger ADHD symptoms. In some cases, certain environmental factors are enough to directly affect the brain to cause ADHD. These factors may be involved:
Preterm birth and low birth weight
An analysis of 12 studies involving more than 6,000 participants showed that being born very premature or with very low birth weight was associated with a threefold increased risk of ADHD . Other studies have found risks that increase with lower birth weight and earlier date of prematurity.
A 2020 analysis of 14 studies involving more than 17,000 children found that higher blood levels were associated with a four-fold higher risk of ADHD compared with the lowest blood levels. Other studies have found that lead exposure may double the risk .
Traumatic brain injury in childhood
The study analyzed 12,374 people who suffered head injuries in childhood and found that severe brain injury early in life increases the risk of developing ADHD later in life. Concussions and minor injuries do not increase the risk .
Fetal Alcohol Syndrome (FAS)
Children with this syndrome, caused by being exposed to large amounts of alcohol before birth, are five times more likely to develop ADHD than children with FAS .
What does not increase the risk of ADHD?
Once thought to be associated with ADHD risk, it turns out these do not increase your chances of this brain disease:
High amounts of sugar, food additives and/or poor diet
There is no evidence that sugary diets and additives cause ADHD. For a small number of children who already have ADHD, sensitivities to certain foods or colorings, preservatives and other additives may play a role, but more research is needed.
Play video games and watch TV
Children and teens with ADHD may become addicted to colorful, fast-paced video games , but according to the Child Mind Institute, there is no evidence that playing these games or watching television increases the risk.
Poor parenting or a chaotic home
The idea that parents cause ADHD stems from the naive observation that children with ADHD often misbehave, and the belief that misbehavior is a sign of poor parenting. There is no evidence that lax discipline leads to the inattention, hyperactivity, and impulsivity that are hallmarks of ADHD.
Three large studies involving more than 200,000 children show that childhood vaccinations do not cause ADHD.
Prenatal exposure to tobacco smoke
ADHD has long been considered a risk, but exposure to tobacco smoke in the womb has been shown to not increase the risk of ADHD, according to a 2022 UK analysis of 45 studies.
Smoking during pregnancy has been shown to be more common among women who are at higher genetic risk for ADHD.