Asthma rates among children have plateaued and started to decrease after steadily increasing for several years, according to a new study from the National Center for Health Statistics. Childhood asthma rates began increasing in 1982 and peaked in 2009 at close to 10 percent, but then leveled off and dropped to 8.3 percent in 2013, according to a study published Dec. 28 in the journal Pediatrics.

"Trends in childhood asthma have recently stopped increasing," Dr. Lara Akinbami, of the National Center for Health Statistics, told HealthDay. "This is mainly due to the leveling off of prevalence among black children, who previously had large increases in the prevalence of asthma. However, more years of data are needed to clarify if asthma prevalence among children will continue to decline, or if it will plateau around current levels."

There was no change in prevalence of asthma among non-Hispanic white and Puerto Rican children or among children overall in the northeast and western regions of the United States. However, rates increased among children aged 10 to 17, poor children and children in the South, according to UPI.

Asthma rates increased and then plateaued among 5- to 9-year-olds, non-Hispanic black children and those close to poverty, while rates increased and then decreased among 0- to 4-year-olds, non-poor, Mexican and Midwestern children.

The researchers said they were not entirely sure why overall rates have leveled or why rates among the impoverished rose slightly. One possible explanation for the decline is a plateau in childhood obesity rates and a decrease in air pollution. The increase among poorer children could be attributed to more exposure to tobacco, mold, mildew, dust, cockroaches and smog. They also tend to live with more stress, which could have an effect on asthma risk, according to CBS.

Researchers used data from the 2001 to 2013 in-person National Health Interview Survey in which more than 150,000 parents were asked if their children had been diagnosed with asthma.