Hyperactivity in young linked to smoking during pregnancy

Children whose mothers smoked during their pregnancy are up to nine times more likely to develop attention deficit hyperactivity disorder, scientists say. US researchers found smoking acts as a trigger for the disorder when children are already genetically predisposed to ADHD.

The dangers of smoking during pregnancy are well documented. But the links between smoking and ADHD have not been proven until now. Symptoms of the disorder usually start early in a child's life. In the US the most recent study indicated that around 3.3% of children under 10 have ADHD and levels are believed to be similar here. The researchers found no relationships between alcohol during pregnancy and ADHD. The scientists contacted just over 5,000 families with twin children aged seven to 18 in Missouri. The parents were asked to complete questionnaires on their children's behaviour and their habits during pregnancy. More than 24% reported smoking during pregnancy, of whom more than 75% smoked during the entire pregnancy.
A significantly increased risk of ADHD was found in those who smoked. "The average number of ADHD symptoms was significantly higher in the offspring who were exposed to prenatal smoking," the study said. Rosalind Neuman, one of the authors, said: "When genetic factors are combined with prenatal cigarette smoke exposure, the ADHD risk rises very significantly."
John Krystal, editor of Biological Psychiatry in which the research will be published in June, added: "These data highlight a new risk of maternal smoking, increasing the risk for ADHD in their children. ADHD, in turn, increases the risk for substance abuse. Thus, it appears in utero exposure to nicotine may help to perpetuate a cycle across generations that links addiction and behavioural problems."
A separate study, published last night, reveals that smoking cannabis while pregnant affects the brain development of unborn babies. Scientists believe taking the drug could restrict naturally occurring compounds in the embryonic brain which join up nerves and promote foetal growth.
The research centres on compounds in the body called endocannabinoids. These act in the same way as cannabis by attaching to receptors found on the surface of nerve cells in the brain. If cannabis is smoked at the same time as these molecules are released, there can be a battle for the receptors. This can disrupt the network of nerves and their formation.
Researchers in Scotland, the US and Hungary have been involved in the year-long study, led by the Karolinska Institute in Stockholm, Sweden. Anne Rajnicek, lecturer at Aberdeen University's institute of medical sciences, said: "Although we did not test marijuana-derived compounds directly, our data suggest marijuana use during pregnancy could affect development of the foetal brain."
Source: The Guardian Friday May 25, 2007