Chicago - Asthma rates in U.S. children have quieted down after a decades-long increase, a government study found, and researchers are trying to pinpoint reasons that would explain the trend.

A possible plateau in childhood obesity rates and declines in air pollution are among factors that may have helped lower cases in kids, the 2001-13 study suggests. Overall, average asthma rates among kids aged 17 and younger increased slightly, then leveled off and declined by the study’s end, when 8.3 percent of kids were affected. Rates varied among some regions, races and ages.

The study was published online Monday in the journal Pediatrics.

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