Growing up near a freeway stunts a child's breathing capacity for a lifetime, significantly increasing the risk of serious lung and heart diseases later in life, according to researchers who monitored thousands of Southern California children for up to eight years.

The study, led by a team of University of Southern California scientists and released Thursday, delivers a sobering answer to a long-standing question about the health effects of being raised near a busy roadway where air is chronically polluted.

These children not only are more likely to develop asthma, but their lung development can be permanently cut short, increasing their odds of having a heart attack or a life-threatening respiratory condition, starting as early as their 50s, the researchers said.

"It's a big risk factor," said James Gauderman, the author and principal investigator of the study by researchers at USC's Keck School of Medicine. "If you've got less lung capacity, and you get hit with the flu or pneumonia, you've got less reserve to fall back on."

The findings carry policy implications for pollution-control agencies and for officials who choose where to locate roads, homes and schools.

The USC study draws data from a long-term, state-funded investigation that has been tracking thousands of children since 1993.

While earlier findings from the children's project were more applicable to urban Southern California, results of the new study should resonate nationwide, Gauderman said.

Even in towns with overall good air quality, he said, "if children are living near a busy road, then our results suggest that they are at increased risk for these kinds of health effects."

The researcher accounted for factors that could skew results such as socioeconomic status, smoking, and breathing disorders such as asthma.

They found that the overall lung capacity of children living within a mile from a freeway was 3 percent below normal.

The performance of their tiniest airways, where oxygen is delivered to the bloodstream, was about 7 percent below normal.