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Parents who teach their children to take care crossing the road may be neglecting a greater danger - living next to it.
Researchers have found that young people growing up in homes within 500m of a main road suffer significant damage to their lungs from exhaust fumes.
Compared with those who live at least 1.5km away the breathing of those in homes closer to the traffic is neither as deep nor as vigorous and their lungs do not develop as well.
The poorer condition of their respiration puts them at greater risk from asthma, bronchitis and chronic obstructive pulmonary disease as adults and weakens their sporting ability, the research suggests.
The study, conducted in California, is the latest to show that air pollution damages the lungs and increases the rate of respiratory diseases. But few studies have examined its effect on lung growth in children.
Scientists from the University of Southern California measured the lung function of 3677 children over eight years from age 10 to 18. They found even healthy children with no history of asthma and who did not smoke suffered ill-effects from exposure to the traffic.
"Since lung development is nearly complete by age 18 years, an individual with a deficit at this time will probably continue to have less than healthy lung function for the rest of his or her life," they write in the online version of the Lancet.
The effect was greater in boys than in girls, whereas a European study had found a greater effect in girls than in boys.
Lung function was measured by checking how big a breath each child could take, and the maximum pressure they could muster when blowing it out.
The measurements were repeated over time to show how the lungs were developing.
The authors say carbon, nitrogen dioxide and ultra-fine particulates - tiny particles that can penetrate deep into the lungs when breathed in - are all raised near traffic-congested roads and could account for the damaging effects. Diesel exhaust in particular has been shown to cause inflammation in the bronchial walls in the lungs.
Pressure on space in many towns and cities is forcing the construction of homes and schools close to "busy roadways", they say.
"In view of the magnitude of the reported effects and the importance of lung function as a determinant of adult morbidity and mortality, reduction of exposure to traffic-related air pollutants could lead to substantial public health benefits."
Professor Stephen Holgate, professor of immunopharmacology at the University of Southampton in Britain, said the study added to evidence that exhaust fumes damaged lung development in children "probably in the first five to eight years of life".
"Reduced lung function in childhood is a known risk factor for the development and worsening of asthma in children and the development of chronic obstructive pulmonary disease later in life," he said, "as well as reducing exercise tolerance and increasing the risk of serious lung infections in childhood."
The World Health Organisation had emphasised the importance of reducing overall air pollutant exposure.
- INDEPENDENT
