March 1, 2024

What are the causes of ADHD? Biology vs. environment

Researchers don’t know the exact cause of attention deficit hyperactivity disorder (ADHD). However, they believe it may develop from a combination of genetic and environmental factors.

ADHD can cause inattention, hyperactivity and impulsivity. Many studies suggest a strong link between genetic factors and ADHD, but this is not the only thing that seems to contribute to it.

Read on to learn more about the causes of ADHD and the research behind them.

ADHD tends to run in families. Identical twins are more probable develop ADHD than non-identical twins. This suggests a genetic component to the disease, as identical twins have the same genes, while non-identical twins do not.

Genes may be responsible 74% of the cause of ADHD. Research into the specific genes involved in its development is still ongoing, but a large number of international 2023 Study estimates that about 7,300 genetic variants may increase a person’s risk of ADHD.

However, many are common variants and do not always cause ADHD. This suggests that it is not just genetics that influence a person’s chances of having ADHD. The number of these variants a person has and other factors can increase the likelihood.

ADHD also appears to cause or originate from changes in the brain. These include:

Brain structure

A 2017 imaging study found that overall brain volume and specific brain regions were slightly smaller in participants with ADHD than in those without ADHD.

Regions included:

  • caudate nucleus and putamen, which coordinate smooth movement
  • nucleus accumbens, which plays a role in processing rewards
  • amygdala, which influences emotional regulation
  • hippocampus, which is involved with emotion and motivation

Differences in brain volume were more noticeable in children with ADHD than in adults. This supports the researchers’ theory that ADHD causes a delay in the development and maturation of several regions of the brain.

Brain function

According to a 2018 review, functional magnetic resonance imaging (fMRI) studies indicate that people with ADHD may have deficiencies in several brain networks that manage attention, cognitive control, time, and working memory.

The review authors also state that people with ADHD may have differences in the brain networks that deal with processing rewards.

For example, the review notes that some research in children with ADHD has found reduced activation in specific regions of the brain when performing reward-related decision-making tasks.

Brain chemistry

Brain chemistry refers to the balance of chemicals that affect a person’s mood and nervous system. One of these brain chemicals is dopamine. This plays a vital role feelings of pleasure, motivation and reward. Dopamine is also involved in motor function, memory and focus, and executive functioning.

On a 2009 studystudy participants with ADHD had lower dopamine levels than participants without ADHD.

Some experts believe that lower dopamine levels may occur in people with ADHD because they have higher concentrations of proteins known as dopamine transporters, which reduce dopamine levels in the brain.

However, researchers still don’t understand the relationship between ADHD and dopamine.

Brain injury

A traumatic brain injury (TBI) is an injury that affects the functioning of the brain.

A 2018 study with children aged 3 to 7 years hospitalized overnight for TBI found that TBI correlated with an increased risk of ADHD up to 7 years after injury.

Specifically, about 62% of children in the study with severe TBI later developed ADHD. This is known as secondary ADHD.

Some research connects ADHD to complications that affect fetal development during pregnancy, such as:

  • Alcohol consumption: A 2015 study found that children who experienced prenatal alcohol exposure were 1.55 times more likely to have ADHD.
  • Prenatal smoking: Some research suggests a link between smoking during pregnancy and an increased risk of ADHD in children. This includes the 2015 study above, which found a 2.64 times greater chance of ADHD due to maternal smoking during pregnancy. However, Search 2022 states that although there is an association, it is unlikely to be causal.
  • Neurotoxins: Some studies suggest that exposure to certain chemicals, such as lead and some pesticides, may have associations with ADHD. For example, a 2016 study found that exposure to organophosphate pesticides can impact brain development and contribute to a greater chance of ADHD.
  • Low birth weight: A 2018 review found that compared to babies weighing at least 5.5 pounds (lb), babies weighing less than 3.3 pounds were at least twice as likely to develop ADHD. Babies weighing less than 2.2 pounds were at least four times more likely to develop ADHD.

Some birth complications are also associated with ADHD, such as:

  • Oxygen deprivation: A 2013 study found that children who lack oxygen to the brain before or shortly after birth were significantly more likely to develop ADHD later in life.
  • Caesarean: A 2019 study compared cesarean section (C-section) birth with vaginal birth. Researchers found a higher rate of ADHD among children born by cesarean section. However, the connection between them is still unclear.
  • Premature birth: A 2022 study found that among children born between 37–41 weeks of gestation, those born before 39 weeks are more likely to experience symptoms of ADHD.

Although these studies show an association between ADHD and prenatal or birth complications, they do not prove that they are a direct cause. More research is needed to understand the relationship.

Psychological trauma may play a role in ADHD, but it’s not clear how or to what extent.

Trauma is an emotional and physical response to an intensely distressing event. In studies of child development, scientists refer to these events as adverse childhood experiences (ACEs). ACEs may include:

  • direct experiences of abuse or neglect
  • witnessing violence
  • live in an unsafe or unstable environment

Children with ACEs are more likely to have ADHD. People with ADHD are more probable have more ACEs.

Scientists don’t know why this happens, but the fact that children with ADHD are more likely to have traumatic experiences may be due to a “cycle of adversity” in which their symptoms make it harder to navigate the world and make them feel less comfortable. most vulnerable to abuse.

Some people believe that ADHD is the result of:

  • eating a lot of sugar
  • watching TV or playing a lot of video games
  • poor parenting

However, the Centers for Disease Control and Prevention (CDC) emphasizes that there is not enough evidence that any of them directly cause ADHD.

For example, a 2019 cohort study looked at children without ADHD symptoms at age 6. Sugar consumption had no impact on the likelihood of ADHD in the group as they aged.

Researchers suggest that higher sugar consumption in people with ADHD may be an effect of impulsivity or hyperactivity. This would be in line with previous research that suggests a link between ADHD and certain eating habits, such as eating more frequently and snacking frequently.

ADHD is also not a product of a lack of parental discipline. In fact, the opposite may be true. A 2022 review found associations between negative or harsh parenting and ADHD, as well as other factors such as:

  • emotional reactivity
  • intrusiveness
  • mistreatment
  • factors that can put pressure on families, such as divorce or incarceration

However, it can be difficult to tell whether these factors cause ADHD or whether they are present because several family members have ADHD. For example, reactivity may result from difficulty regulating emotions or impulses.

ADHD appears to be something a person has from birth or develops in early childhood.

According to the National Institute of Mental Health, symptoms of ADHD can begin between ages 3 to 6 years.

Researchers are still learning about the causes of ADHD. However, they suspect that a combination of genetic and environmental factors increases a person’s chances of developing the disease.

Despite popular belief that sugar, too much TV, or a lack of discipline cause ADHD, there are there is not enough evidence To conclude, they contribute to the condition.

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