The exact cause of attention deficit hyperactivity disorder (ADHD) is not fully understood. It is thought that ADHD is caused by a mix of genetic (inherited) and environmental factors.
Genetics
ADHD tends to run in families and, in most cases, it is thought that inheriting the condition is the most likely cause. Research shows that both the parents and siblings of a child with ADHD are four to five times more likely to have ADHD themselves.
Brain function and anatomy
Although the exact cause of ADHD is still unclear, research shows that the way the brain works in people with ADHD differs from that of people who do not have the condition. It is thought that chemicals in the brain that carry messages, known as neurotransmitters, do not work properly in people with ADHD. Also, people with the condition seem to display less activity in the parts of their brains that control activity and attention.
Some research shows that the frontal lobes, which are the part of the brain that control decision-making, do not work as they should in people with ADHD. Other research indicates that they may have imbalances in the levels of certain chemicals, such as noradrenaline and dopamine.
Exposure to toxins during pregnancy
Women who smoke when they are pregnant are more likely to have a child with ADHD. Drinking alcohol and drug abuse can also increase the risks of ADHD in an unborn child.
Being male
Boys are more commonly diagnosed with childhood ADHD than girls, and more men are diagnosed with the condition than women. Research suggests this could be because diagnosis tends to pinpoint loud, disruptive behaviour, which is more noticeable and more common in males than in females.
It could also be that ADHD is missed in girls because they tend to have the form of the condition defined by inattentiveness (ADHD mainly inattentive, or attention deficit disorder).
Excessive exposure to television
There have been several studies that have looked at the relationship between children watching a lot of television at a very young age and the development of ADHD in later childhood.
There is not enough evidence to say that television is definitely a cause of ADHD, but allowing children up to the age of three to watch several hours a day could contribute to attention problems and ADHD in later life.
Food intolerance
Food intolerance is not a direct cause of ADHD, but some studies have suggested that there may be a link between childhood ADHD and common food allergens, such as:
There is no evidence that sugar causes the symptoms of ADHD.
Other causes
Other possible causes of ADHD include:
- being born prematurely (before week 37 of the pregnancy)
- having a low birth weight
- brain damage either in the womb or in the first few years of life
- having a hearing impairment
