For many years, urban living has been widely regarded as a risk factor for asthma. More than half a century ago, experts spoke of an “inner-city asthma epidemic” which public health efforts focused on tackling. However, a new study suggests that the association between urban living and asthma has been overestimated.
Instead, the study, published in the Journal of Allergy and Clinical Immunology, finds that ethnicity, race and income are more significant risk factors for the development of the respiratory disease.
According to the Centers for Disease Control and Prevention (CDC), around 18.7 million adults and 6.8 million children in the US have asthma. It is not clear precisely what causes the condition, but experts currently believe that it is most likely due to a combination of environmental and hereditary factors.
Air pollution and pest allergens are known to trigger symptoms of asthma and could more likely be encountered in urban environments. According to information provided in the study, however, the prevalence of asthma in inner-city areas across the US is unknown.
Researchers from the Johns Hopkins Children’s Center set out to estimate the prevalence of asthma in both inner-city and non-inner-city areas of the country, as while investigating the influence of other factors on asthma risk. They write:
“Understanding whether asthma disparities seen in various geographic areas are primarily a result of environmental exposures concentrated in the inner city or are instead related to sociodemographic features of the inhabitants of these neighborhoods is key to advancing an efficient and effective national research and public health agenda.”
In an assessment of 23,605 children aged 6-17, the team surveyed parents and caregivers in order to compare rates of childhood asthma in cities and outside of them.
No difference was reported in asthma risk among children living in urban areas and those living in suburban and rural areas, once variables such as ethnicity, race and geographic region were included in the analysis.
Some suburban and rural areas were even found to have higher rates of asthma prevalence than corresponding inner-city areas. For example, in the Northeast, asthma prevalence in low-income suburban areas was 21%, compared with 17% in local urban areas.
However, an association was noted between a higher-than-average asthma risk and poverty, African-American race and Puerto Rican ethnicity.
The lower a family’s annual income, the higher the risk of its children being diagnosed with asthma or having emergency treatment for asthma. The researchers found that family poverty was a much stronger influence on asthma risk than living in a poor neighborhood.
Asthma prevalence was also much higher among African-American children (17%) and children of Puerto Rican descent (20%) and these factors remained influential even after adjusting results for neighborhood poverty and household income. In comparison, rates of asthma were 10% of white children, 9% of Hispanic children and 8% of Asian children.
The researchers state that African-Americans and Puerto Ricans have previously been identified as being at a higher risk of developing asthma, potentially due to biological and genetic differences.
“Our results highlight the changing face of pediatric asthma and suggest that living in an urban area is, by itself, not a risk factor for asthma,” says lead investigator Dr. Corinne Keet. “Instead, we see that poverty and being African-American or Puerto Rican are the most potent predictors of asthma risk.”
Factors that fuel asthma risk such as the aforementioned air pollution and pest allergens, along with higher rates of premature births and exposure to indoor smoke, have been predominantly associated with urban environments. The findings suggest that these factors may no longer be solely confined to cities.
“Our findings suggest that focusing on inner cities as the epicenters of asthma may lead physicians and public health experts to overlook newly emerging ‘hot zones’ with high asthma rates,” states senior author Dr. Elizabeth Matsui.
The study is limited by the use of fairly crude self-reporting to measure asthma prevalence. The authors acknowledge this, but believe that such weakness is countered by the strengths of their sample, which is both large and nationally representative.
Asthma risk was also measured purely on whether the children had asthma or not and so the study’s findings do not detail how severe the participants’ asthma symptoms were. A separate investigation focusing on associations between living environment and asthma severity has begun, the authors report.
“[Demographic] changes challenge the use of ”inner city” as interchangeable with black race and mean that focusing on the inner city might not fully capture the population most at risk for asthma,” write the authors.
Last month, Medical News Today reported on a study revealing that toddlers who sleep in the same bed as their parents may be at increased risk of developing asthma.