One-third of all children with attention deficit problems can blame their disability on their mothers smoking in pregnancy and on lead pollution, according to an official US study.
The research, which has been hailed as a "landmark", casts light on the causes of attention deficit hyperactivity disorder (ADHD), which blights the lives of hundreds of thousands of children and their families.
About half a million children in Britain may have the disability, 100,000 of them severely, according to the National Institute for Health and Clinical Excellence. Prescriptions of Ritalin, the main drug used to treat it, have soared 180-fold over the past 15 years and now exceed 350,000 a year.
The study - carried out at the Cincinnati Children's Hospital Medical Center - looked at 4,704 children between the ages of four and 15. It found that those born to mothers who smoked in pregnancy were two and a half times more likely to develop the condition than the children of non-smokers, while those with even relatively low levels of lead in their blood suffered four times the risk.
The research provides a blue-chip confirmation of previous studies suggesting a link between ADHD and smoking. But its results on lead are more alarming as it suggests that even levels thought to be safe cause the disorder.
The fourfold risk was found in children with between two and five microgrammes of the toxic metal per decilitre of blood - between a fifth and a half of the safety level laid down by the World Health Organisation.
Although banned from petrol worldwide (it was withdrawn from general sale in Britain in 2000), leadpersists in dust - the result of decades of emissions from exhausts - and in pipes and paint in some old buildings.Reuse content