Children who live near a busy road are more likely to develop ADHD

Unborn babies and infants exposed to high levels of traffic pollution are more likely to become hyperactive

Unborn babies and infants exposed to high levels of traffic pollution are more likely to become hyperactive, researchers have warned.

Scientists believe that early life exposures to a variety of toxic substances are important in the development of problems later in life.

The study suggest by the age of seven, children exposed to the substances are more likely to test positive for attention deficit hyperactivity disorder (ADHD) and related symptoms, including lack of attentiveness, aggression, and behavioural problems.

Traffic particulates may cause narrowed blood vessels in the body and toxicity in the brain's frontal cortex, it was suggested.

Dr Nicholas Newman, from the Cincinnati Children's Hospital Medical Centre in the U.S., said: ‘There is increasing concern about the potential effects of traffic-related air pollution on the developing brain.

‘This impact is not fully understood due to limited epidemiological studies.

‘To our knowledge, this is the largest prospective cohort with the longest follow-up investigating early life exposure to traffic-related air pollution and neurobehavioral outcomes at school age.’

The team collected data on traffic-related air pollution (TRAP) from the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS), a long-term epidemiological study examining the effects of traffic particulates on childhood respiratory health and allergy development.

Children born in the city between 2001 and 2003 were chosen based on family history and whether they lived near to or far from a major highway or bus route.

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Children were followed from infancy to seven when parents completed a questionnaire about their behaviour.

This assessed attention deficit hyperactivity disorder (ADHD) and related symptoms including attention problems, aggression, conduct problems and atypical behaviour.

Of the 762 children initially enrolled in the study, 576 were included in the final analysis at seven years of age.

Results showed that children who were exposed to the highest third amount of TRAP during the first year of life were more likely to have hyperactivity scores in the ‘at risk’ range when they were seven years old.

Traffic particulates may cause narrowed blood vessels in the body and toxicity in the brain's frontal cortex - this could result in ADHD in children

The ‘at risk’ range for hyperactivity in children means that they need to be monitored carefully because they are at risk for developing clinically important symptoms.

Dr Newman added: ‘Several biological mechanisms could explain the association between hyperactive behaviours and traffic-related air pollution, including narrowed blood vessels in the body and toxicity in the brain's frontal cortex.’

However, higher air pollution exposure was associated with a significant increase in hyperactivity only among those children whose mothers had greater than a high school education.

Mothers with higher education may expect higher achievement, he says, affecting the parental report of behavioural concerns.

He said: ‘The observed association between traffic-related air pollution and hyperactivity may have far-reaching implications for public health.

Previous studies have shown that approximately 11 per cent of the U.S. population lives within 100 meters of a four-lane highway and that 40 per cent of children attend school within 400 meters of a major highway.

He said ‘Traffic-related air pollution is one of many factors associated with changes in neurodevelopment, but it is one that is potentially preventable.’