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Attention-deficit hyperactivity disorder (ADHD) and attention-deficit disorder (ADD) refer to a range of problem behaviours generally associated with poor attention span. Symptoms include restlessness, hyperactivity and inattentiveness, often leading to problems with academic achievement, both in terms of language and literacy skills, as well as a reduced ability to cope with certain social situations. Core symptoms include an inability to remain attentive or to concentrate, the propensity to become very easily distracted, as well as the display of inappropriate levels of activity and impulsivity. The activity is sometimes characterised by fidgeting and general restlessness; the impulsivity can present itself as inappropriate speech (i.e. blurting out words when it is not suitable to do so) or hitting out. Children with ADHD may be unable to sit still or pay attention in the classroom, for example. In general, ADHD is a persisting disorder with many children continuing to have significant difficulties in adulthood. ADHD is thought to affect about 3–9% of school age children and young people in the UK, and about 2% of adults worldwide.

The causes of ADHD are still somewhat unclear, although it is believed that a combination of genetic, environmental and dietary factors all contribute to risk. Scientists will often use twin studies to evaluate genetic links to many disorders and diseases. For example, if one identical twin has ADHD, it is more likely that the other will also have, or later develop, symptoms as well. Whilst this genetic link is becoming clearer, it is unlikely that one gene alone is responsible but that ADHD is caused in part by several genes, which all make a small contribution to the onset of this disorder. ADHD is a condition which falls within a class of disorders termed ‘neurodevelopmental disorders’. Simply put, neurodevelopmental disorders are due to an impairment of the growth and development of the brain or central nervous system. Some of the genes which are thought to contribute to the development of ADHD are genes that control certain types of neurotransmitters (chemicals involved in signalling between nerve cells in the brain). Defects in one or more of these genes may contribute to a greater risk of developing ADHD. Two well-studied genes are those that control the production of dopamine and noradrenaline, levels of which are often low in ADHD. Both of these neurotransmitters are heavily involved in behaviour. It’s not all about our genes, of course. It appears that people with ADHD can have abnormalities in certain areas of the brain which control activities associated with self-control and result in the core symptoms of ADHD – hyperactivity, impulsiveness and inattention. To summarise, it is thought that an imbalance of some of the neurotransmitter chemicals in the brain and changes in the structure of areas of the brain play a key role in ADHD. Environmental factors These are factors that are associated with a higher risk of ADHD but do not involve our genes – in other words we do not inherit an increased disposition. Environmental factors in ADHD could include complications during pregnancy, at birth or shortly after birth. Increasing exposure to toxic chemicals is also thought to play a role in ADHD risk. For example, smoking, drinking alcohol or use of drugs during pregnancy, or even high levels of stress whilst pregnant, can all affect the development of the baby’s brain.

Some studies have found that children with ADHD have lower levels of long-chain fatty acids than other children. It is suggested that individuals with ADHD may not absorb these essential fatty acids from food as well as other people, or that they lack the enzyme that converts short-chain fatty acids from foods we eat to the important eicosanoid-producing fatty acids (EPA and DHA in particular, which can be directly sourced from oily fish). Another hypothesis is that the turnover of these long-chain fatty acids is elevated and the body cannot replenish them at a fast enough rate. Direct supplementation is therefore a sensible way to overcome both possibilities: either an inability to produce them physiologically or an increase in their turnover necessitates higher intake of these essential nutrients. As low omega-3 levels are associated with low levels of dopamine, a neurotransmitter known to be dysfunctional in ADHD, supplementing any imbalances or deficiencies may improve behavioural and learning difficulties associated with the condition. Studies are supporting this approach, with results suggesting that by supplementing the diet of a child with ADHD with purified fish oil, improvements are seen in relation to inattention, hyperactivity and impulsivity, when compared to a placebo. What appears to be most interesting, however, is that the overall evidence from different randomised, placebo-controlled, double-blind studies shows that EPA, rather than DHA, may be the omega-3 fatty acid most effective in tackling the symptoms of ADHD.