(Reuters Health) - Much of the variation in smoking rates across American cities can be explained by the higher density of tobacco retailers in poor, nonwhite neighborhoods, a study of the 500 largest U.S. cities suggests.

Researchers examined data on socioeconomic factors like income and education level as well as survey data on current smoking rates, asthma, chronic obstructive pulmonary disease (COPD), and coronary heart disease for census tracts across U.S. cities in 2014. They also used a private business database to assess the likely number of tobacco retailers in each census tract, an area that typically spans several city blocks and can encompass entire communities.

Most of the inequity in smoking rates - 56 percent of the total variation - occurred between different census tracts within the nation’s largest cities, and just 44 percent occurred between different cities, the analysis found.

“There are likely several explanations for the greater within city variation, but one that these data bear out is the presence of income and race segregation,” said lead study author Eric Leas of the University of California, San Diego.

“U.S. cities have class and race divides and smoking follows similar class and race divides, where lower income or non-white populations tend to live in the same neighborhoods and smoke at higher rates,” Leas, who did the work while at Stanford University in California, said by email. “While class and race divides occur between U.S. cities, they are more prominent within U.S. cities.”

Within individual cities, census tracts with higher smoking rates had more tobacco retailers, lower typical household income, and a smaller percentage of white residents than census tracts with lower smoking rates, researchers report in JAMA Internal Medicine.

While all cities had some inequity in smoking rates across various neighborhoods, some cities stood out.

Washington, D.C. had the most variation in smoking rates across different communities within its borders, followed by Atlanta, Fort Lauderdale and Miami.

Census tracts with higher smoking rates also tended to have more smoking-related illnesses like asthma, COPD and heart disease, the study also found.

In the 10 percent of census tracts in the study with the lowest smoking rates, no more than about 11 percent of people smoked. In the 10 percent of census tracts with the highest smoking rates, at least about 28 percent of people smoked, the study found.

A change from neighborhoods with the lowest to the highest smoking rates was associated with a 39 percent increase in asthma rates, a more than doubling in COPD rates, and a 27 percent increase in the prevalence of heart disease, the study found.

The study wasn’t a controlled experiment designed to prove whether or how specific neighborhood or individual characteristics might directly impact rates of smoking or related illnesses.

Even so, the results offer fresh insight into why smoking rates might be declining nationwide by bypassing certain communities, said Stephanie Mayne, a researcher at the Children’s Hospital of Philadelphia and the University of Pennsylvania who wasn’t involved in the study.

“Tobacco retailers often concentrate in lower income neighborhoods with higher proportions of non-white residents, and these neighborhoods have higher smoking rates,” Mayne said by email. “This matters because, even as smoking rates go down over all, inequalities in exposure to the harms associated with smoking may continue to rise.”

“There are disparities in smoking rates and successfully quitting smoking by socioeconomic status, and when neighborhoods have more tobacco retailers, residents are exposed to more tobacco advertising on a regular basis,” Mayne added. “Restricting sales of tobacco might help by reducing neighborhood residents’ exposure to tobacco advertising.”

SOURCE: bit.ly/2FdEgge JAMA Internal Medicine, online January 7, 2019.