(Reuters Health) - Doctors have long predicted that less air pollution will produce healthier lungs. Now a first-of-its-kind study of 2,120 children in southern California has documented dramatically better lung function growth as air quality has improved.
Over a 13-year period, the proportion of children with poor lung capacity and lung health fell by half as levels of nitrogen dioxide and particulate matter dropped. The gains were seen both in youngsters who had asthma and in those who did not.
“It certainly supports the efforts that have been made over 40 years to improve air quality,” chief author Dr. James Gauderman of the Department of Preventive Medicine at the University of Southern California in Los Angeles told Reuters Health. “We would expect improvements in other urban centers to produce similar improvements in children’s health.”
The study, published in the New England Journal of Medicine, complements research showing that childhood lung function deteriorates and the risk of asthma rises as pollution levels rise.
"This is an association study, so there's always a question of cause and effect. Maybe these people got healthier on their own, ate better diets. You can never say it's an absolute proof," said Dr. Norman H. Edelman, senior consultant for scientific affairs at the American Lung Association.
"But it's not a standalone study. It's based on older studies that show an association between the degree of air pollution and lung function in kids. This turns around and looks at improvement," he told Reuters Health.
Gauderman and his colleagues examined the long-term effects in children by studying three groups during three time periods between 1994 and 2011. Typically, the children entered the study around age 11 and were followed for four years, a period when the lungs are developing rapidly. All lived in the Los Angeles area, a region of the U.S. known for air pollution problems, which have been abating as a result of strict state controls.
“We looked at the proportion of children whose lung function was below 80 percent of normal. That’s a cutoff a physician will often use to flag a person for a possible issue with their lungs,” Gauderman said. While 7.9 percent of children fell into that category in 1998, the proportion had dropped to 3.6 percent by 2011.
“We certainly suspected that improving air quality would improve children’s health,” Gauderman said. “We were surprised by the magnitude of the effect that we’ve seen.”
"What's news about this is the large magnitude of the effect, from 8 percent down to 4 percent," said Edelman, who was not connected to research. "Asthma is present in 10 percent of the population and that's a major health problem. If a percentage of those kids is going to have worse asthma because the air pollution has limited their lung growth, that's a big deal."
During the study years, the air improved “dramatically,” Gauderman’s team writes in their report. For example, in 1994-1997, each cubic meter of air in one of the most-polluted communities, Mira Loma, had 31.5 micrograms of small particles called PM2.5 that penetrate deep into the lungs. By 2007-2010, Mira Loma averaged 17.8 micrograms of PM2.5 per cubic meter of air, a 43 percent decline. All five study sites had significant drops in particle pollution and nitrogen dioxide, they note.
Overall, average lung capacity increased by 91.4 milliliters for every decrease of 14.1 parts per billion in nitrogen dioxide. It rose by 65.5 ml for each decrease of 8.7 micrograms per cubic meter of particle pollution. Significant changes were not linked to ozone levels, but levels of that pollutant have not declined as dramatically over time.
“There were significant effects on lung-function growth in both boys and girls, although the magnitude of the air-pollution effect was significantly larger in boys than in girls,” the researchers conclude.
“We found no significant association between growth in height and change in pollution during the study period, which indicates that our findings on lung-function growth are probably not the result of a secular trend in general development,” they write.
California has stricter pollution controls than the U.S. as a whole, but Edelman said even the federal clean air act has cleaned up a lot of pollution "and this study is part of that. We're making progress. There's still a long way to go. We still have much more unacceptable effects of air pollution than we should have."
SOURCE: bit.ly/1GICJGO New England Journal of Medicine, online March 4, 2015.