Attention-deficit hyperactivity disorder (ADHD) is caused by differences in neurotransmitter patterns in certain parts of the brain (specifically, the cerebral cortex).
Neurotransmitters are chemicals that make it possible for nerve impulses to travel from one nerve cell to another, and therefore play an essential role in the functioning of the brain.
The brain performs a vast range of tasks or functions, allowing us to see, hear, think, speak and move. Each function is performed by a different part of the brain.
In individuals with ADHD, there are lower-than-normal levels of certain neurotransmitters (especially dopamine) in the regions of the brain that are responsible for regulating behaviour and attention.
Research also confirms that the norepinephrine system is involved in some people with ADHD. Norepinephrine is another neurotransmitter found in the brain and body.
Other potential causes include:
- Genetics: ADHD has a genetic component and a group of ADHD-related genes has been identified. The genetic component is confirmed with epidemiological studies looking at family groups. Research has shown that, in identical twins, there’s an almost 100% chance that, if one of the twins has ADHD, the other twin will show symptoms, too. In general, ADHD is genetically inherited in nearly 80% of cases.
- Neurological damage: ADHD can also be present in some people with neurological damage occurring either before or after birth.
- Developmental disorders: Certain developmental disorders or syndromes, like foetal alcohol syndrome, are associated with a higher incidence of ADHD.
- Dietary factors: Diet is often cited as the cause for ADHD, and individuals who suffer from malnutrition or who follow a nutrient-poor diet may indeed experience some of the symptoms. In a small subgroup, dietary factors (e.g. preservatives) may play a role in the worsening of symptoms (e.g. impulsivity and hyperactivity in younger children). Ongoing research is looking at the protective role that essential fatty acids may play in some people.
- Environmental factors: Factors that may play a role in causing ADHD are low birth weight, pregnancy and birth complications, as well as smoking during pregnancy. Note that poisoning with heavy metals like lead creates a similar clinical picture in some people.