Children who live near a noisy road may be at an increased risk of hyperactivity, according to a new study from Germany.

Children in the study who were exposed to the highest noise levels at home showed 28 percent more symptoms of hyperactivity and inattention than kids exposed to the lowest traffic noise levels.

A growing number of studies are showing that environmental stressors, including noise and chemical pollution, may affect children's behavior and mental health, said Michelle Bosquet, a psychologist at Boston Children's Hospital.

Environmental triggers such as traffic noise may impact a child's brain during important developmental periods, increase levels of circulating stress hormones or disrupt a child's ability to sleep and concentrate, said Bosquet, who was not involved in the study.

Previous studies have found an association between exposure to road traffic and aircraft noise at school and child learning problems, though little research has focused on motor vehicle noise at home.

In the new study, researchers led by Carla Tiesler at the Helmholtz Zentrum German Research Center for Environmental Health looked at 900 children living in Munich. The researchers measured noise levels outside of each child's home at the wall of the house, and asked parents to complete a questionnaire about their 10-year-olds' behavior.

Children whose homes had the highest levels of noise at the wall farthest from the road were more than twice as likely to show abnormal emotional symptoms such as excessive worrying or clinginess in new situations than children whose houses may have been quieter. These children also tended to have more problems falling and staying asleep.

One strength of the new study “is its assessment of noise exposure in an environment where children spend the majority of their time, including their sleeping time,” Bosquet said.

After the researchers accounted for sleeping problems, the association between road noise and emotional symptoms decreased, suggesting that sleep problems rather than road noise may be partly responsible for the emotional problems.

According to the Centers for Disease Control and Prevention, about 8 percent of U.S. kids between ages 3 and 17 have been diagnosed with attention deficit hyperactivity disorder.

Dr. Andrew Adesman, chief of Developmental and Behavioral Pediatrics at Cohen Children's Medical Center of New York, said that sleep problems and ADHD are a chicken-and-egg problem.

“It's unclear which comes first,” Adesman said. “Sleep deficit can mimic symptoms of ADHD in kids, though kids with ADHD also tend to have more sleeping problems.

While the study's authors accounted for such factors as families' income levels and children's physical activity levels, which are known to influence child behavior, they cannot say for sure that the association they found was indeed due to road traffic noise, and not some other variable that they did not measure.

The researchers noted they did not measure actual noise levels inside the homes. Some buildings may be better insulated against noise than others, so the noise levels at the outside wall of the home may not reflect the noise experienced within.

The study also did not look at chemical pollution from vehicles, which could explain some of the findings, Adesman said. Previous studies have linked pollution from traffic exhaust to behavior problems in kids.

Bosquet said, “We have much to learn about the mechanisms by which stressors such as traffic noise may influence child health outcomes and how different environmental stressors may interact with each other.”

The study was published online in March in the journal Environmental Research.

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