Medicine is not altogether sure what causes ADHD, but generally classifies it as a 'brain disorder', a 'biochemical imbalance' or 'biological dysfunction'. Despite these widely touted causes, an expert panel to the US National Institute of Health has said there is no valid, reliable or independent test, and that there were "no data to indicate that ADHD is due to a brain malfunction" or that it might be a disease state or brain pathology.
There has been far more progress made by independent researchers, and especially, in the UK, by the Hyperactive Children's Support Group, which suggests that ADHD may be a sign of essential fatty acid (EFA) deficiency. In the USA, the late paediatrician Dr Benjamin Feingold discovered a link with synthetic additives in processed foods. He developed a special diet, which eliminated foods, and especially fruits, that contain natural salicylates, as they prohibit the conversion of long-chain polyunsaturated fatty acids to prostaglandins.
There is also growing evidence that ADHD may be a marker for zinc deficiency, and heavy metal toxicity, such as lead, cadmium and mercury.
Scientists knew back in 1975 that a zinc deficiency caused hyperactivity in rats, and that food additives such as tartrazine can trigger hyperactive behaviour in children.