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Asthma Disparities: Unraveling the Causes

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Higher exposure to air pollutants, reduced access to quality health care and psychological distress are among factors contributing to increased symptoms for children and adults from low-income communities.

THE MORE THAN 5 MILLION CALIFORNIANS who have been diagnosed with asthma represent a cross-section of the state: men, women and children of all ages, ethnicities, household incomes and geographic regions. But when it comes to how people experience this chronic lung disease, asthma tends to be much more discriminating.

Researchers at the Fielding School’s UCLA Center for Health Policy Research have found that Californians with asthma who are from low-income families have more frequent symptoms, end up in the emergency department or hospital more often, and miss more days of work and school than those in higher-income brackets. Analyzing data from the center’s California Health Interview Survey (CHIS), the researchers reported that of the more than 600,000 Californians experiencing frequent (daily or weekly) symptoms, 32 percent of adults were from families earning less than 200 percent of the federal government’s poverty standard – amounting to $41,300 for a family of four at the time of the study. Low-income children missed twice as many days of school due to asthma as children from higher-income families. The research team was headed by Dr. Ying-Ying Meng, senior research scientist at FSPH’s UCLA Center for Health Policy Research and co-director of the center’s Chronic Disease Program.

Other research has similarly shown that racial and ethnic minorities as well as low-income Californians suffer disproportionately from asthma attacks and asthma-like symptoms. What accounts for the differences? In a 2013 study funded by the California Air Resources Board, Meng and her FSPH colleagues sought to determine whether the disparity in the asthma experience has to do with low-income populations’ greater vulnerability (including such factors as lack of access to quality health care and the existence of other chronic conditions), or to exposure to higher levels of air pollutants. The answer was both.

Linking CHIS data to existing air pollutant and traffic data, the Fielding School team found that low-income populations and racial and ethnic minorities (including Latinos, African-Americans, and Asian/Pacific Islanders) were exposed to greater levels of certain air pollutants, including nitrogen dioxide and particulate matter; in turn, they suffered increases in asthma-related difficulties. “These populations are more likely to live near heavy-traffic freeways and in areas where there are industrial pollutants,” says Meng.

But Meng’s group also found that even when low-income and minority populations experienced the same exposure levels as higher-income populations, they had higher rates of asthma-related symptoms, emergency department visits and hospitalizations. “Many factors are involved,” Meng says. In addition to issues of access to quality care, she notes that low-income populations may be more likely to experience other environmental triggers such as exposure to secondhand smoke and substandard housing conditions, including the presence of mold and lack of insulation.

Gretchen Bandoli, an FSPH doctoral student in the Department of Epidemiology, has similarly found that even when taking into account air pollution exposures, adolescents in stressful environments are more likely to suffer from reduced lung function, a predictor of asthma. While previous studies have associated both air pollution and psychosocial stressors with reduced lung function in children and adolescents, Bandoli’s was among the first to account for both factors in the same model – enabling her to assess the impact of each on its own. She has found that higher exposure to certain air pollutants is associated with reduced lung function, but so are psychosocial stressors such as the absence of a father in the house and the perception of family conflict, particularly in older male adolescents. “Studies are increasingly showing that psychosocial stressors to children and adolescents can be detrimental to many of their health outcomes, including something as objective as a lung-function measure,” Bandoli says.

For Meng, the understanding that both environmental and psychosocial factors are contributing to disparities in asthma-related problems begs the question of what can be done to improve outcomes for the most vulnerable populations. “We need to do more at the policy level, from not building low-income housing near freeways and improving housing conditions to reducing traffic-related emission exposures,” she says. “Asthma has the potential to be debilitating, but it can be effectively controlled through appropriate medical care and avoidance of triggers.” •