This article comes from a question from a reader, who asks: “I wanted to ask you, what causes ADHD (Attention Deficit Hyperactivity Disorder)? There is so little information about the causes of ADHD it seems the medical world is at a loss for words. Also if we new what caused it we might be able to cure it rather than treat it.”
(N.B. For this article, and throughout this blog, I use the term ADHD for both ADD and ADHD.)
We will approach this question in two ways:
1) What causes ADHD - in other words - what leads a person to get ADHD in the first place?
2) What causes ADHD symptoms - in other words - when one has ADHD, what leads them to have symptoms of not being able to pay attention, and being hyperactive/impulsive?
Part 1: What causes ADD or ADHD?
The first place to start with the cause of ADD or ADHD is genetics. ADHD is a very genetic disorder.
There is term called ‘heritability’, which refers to how genetic a disorder is. As an example - breast cancer is 30% heritable - meaning that about 30% of the possible causes of breast cancer can be attributed to genetics. Asthma is 40% heritable. Height is 80 to 85 percent heritable. ADHD is about 80 percent heritable.
That means that ADHD is highly genetic. This research comes from twin studies and other family studies, and shows that ADHD is almost as genetic as height.
Now if genes cause 80 percent that means there is about 20 percent that is not caused by genetics. What are the other causes? When it comes to the non-genetic causes of ADHD, we can call these ‘acquired’ cases. When we look at acquired cases, we can separate these into: Prenatal (i.e. causes that affect the person before birth), and Postnatal (i.e. causes that affect the person after birth).
The Prenatal Causes of ADHD:
These are the acquired causes of ADHD that occur during the pregnancy.
- Mother smoking during pregnancy: if the mother smokes cigarettes during pregnancy this increases the risk by 2.5 times (so the child is 2.5 times more likely to develop ADHD than if the mother didn’t smoke during pregnancy)
- Mother drinking alcohol during pregnancy: With alcohol during pregnancy, there is the same increased risk - 2.5 times.
- Prematurity: If there is prematurity at birth, there is a general increased risk for ADHD, however if there is bleeding in the baby’s brain there is a 45 percent chance that that individual will have ADHD.
- Increase in pregnancy complications: If there is an overall increase in pregnancy complications there is a non specific increased risk for ADHD.
Interestingly cocaine or crack exposure is not a risk factor for ADHD once you account for smoking cigarettes and drinking alcohol. Generally speaking a pregnant mother who is using cocaine will also tend to use cigarettes and alcohol.
The Postnatal Causes of ADHD:
These are acquired causes of ADHD that occur after the pregnancy (i.e. after the child is born).
- Head injuries/head Trauma: ADHD can develop after a significant head injury - by significant I mean one that results in loss of consciousness, or a serious concussion
- Brain Hypoxia which means not enough oxygen getting to the brain for a period of time. An example of this could be a near drowning or some other situation like that.
- Brain tumours
- Brain infection.
- Lead poisoning in the preschool years (i.e. before 3 years old)
- Survival from acute lymphoblastic leukemia (ALL) - because the chemotherapy itself can lead to brain changes.
Part 2: What Causes ADHD Symptoms?
The first place to start when talking about what causes ADHD symptoms is the fact that ADHD is a brain disorder. All of the research going into ADHD shows clearly that differences in the ADHD brain are what account for the symptoms.
This means that we can throw out the causes of ADHD which are ’social’. In other words, all of the descriptions of ADHD coming from: video games, TV, MTV, single parents families, stressed school systems, etc. are all wrong! There is no credibility to these explanations.
Brain research in ADHD is continually improving and progressing. Brain imaging shows that the main area of the brain involved in ADHD symptoms in the prefrontal cortex. This is in the frontal lobe - the part of the brain just behind the forehead. The frontal lobe is the command center of the brain. This is the part that does the planning that we need to do. The frontal lobe tells you to pay attention to this and disregard that because it’s a distraction that’s not important. It tells you to plan, it tells you how to adapt your plan when something comes up that’s difficult. It tells you to inhibit your response - so you don’t swear at someone, even if you’re angry, if it would get you into serious hot water.
So the prefrontal cortex, the part of the brain in the frontal lobe just behind the forehead, is the part that’s involved in ADHD.
Brain imaging studies that look at the brain chemicals - called neurotransmitters - show that there is a decrease in the brain chemical dopamine in that area. Another brain chemical impacted in ADHD is norepinephrine (or noradrenaline). Now when a person with ADHD takes an ADHD medicine, it increases the dopamine and/or noradrenaline. This improves the concentration, hyperactivity and impulisivity. If you examined that person under a PET scan - you would see that there is an increase in these brain chemicals in the area that is impacted
Parenting and ADHD:
While we are talking about the causes of ADHD, I need to take a moment and address this important issue: parenting and ADHD. It is very common in society at large to blame parents for their children’s ADHD and/or misbehavior associated with ADHD.
Bad parenting does not cause ADHD. This has been conclusively proven. I’ll repeat it: Bad parenting doesn’t cause ADHD.
If anything, having an ADHD child is very stressful, presents unique challenges, and creates low parenting satisfaction. Why? Because of the ADHD.
As a child psychiatrist and a parent myself - my experience is that most people have kids, and despite the fact that they are not experts in parenting, they try hard (and maybe learn about parenting through reading or classes) and their child turns out fine. You can call this ‘natural intuitive parenting’. Parents then pat themselves on the back and say ‘I’m a great parent’.
In contrast, the parent who has a child with ADHD can do the exact same things but they just don’t work. Instead of them being able to pat themselves on the back, everybody is trying to tell them how to parent their child because their child just doesn’t seem to listen. This leads to a lot of parenting frustration, and it makes it harder for the parents.
Research has shown that when parents use specific strategies designed to help with ADHD, this can improve their effectiveness as parents, and we will cover this more in a future article.
In this article, we have covered the causes of ADHD - i.e. what leads to a person having ADHD. This is mainly genetics, but some acquired causes as well. We have also talked about what causes ADHD symptoms - i.e. the brain! To finish the article, I covered the issue of parenting and ADHD - and how bad parenting is not a cause of ADHD.
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