The decision by two national dollar store chains to sell tobacco has negatively affected the smoking rate among pregnant women in six Southeastern states, new research has found. In counties with the largest increases in tobacco availability, researchers found the smallest drops in smoking among pregnant women.

The findings by University of Florida Health researchers used public data to track tobacco availability and smoking rates over a number of years. They focused on two seminal events — the two dollar store chains’ decisions in late 2012 and early 2013 to begin selling tobacco in their 8,300 Southeastern stores and a move by the nation’s largest pharmacy chain two years later to end tobacco sales at its 2,500 stores, including those in the Southeast.

The largest drop in smoking among pregnant women occurred in counties that had no change in the number of tobacco retailers. Among pregnant women in lower-income communities, smoking rates fell only 3.6 percent in areas where more stores sold tobacco products. But the rate fell 12 percent in areas that saw a only slight increase in the number of tobacco sellers.

The study found increased access to tobacco may be inhibiting programs aimed at reducing tobacco use even after socio-demographics were considered.

The concentration of tobacco sellers also was significant. Researchers said the findings are important for local officials who could use the information to develop property zoning and licensing guidelines to regulate clusters of tobacco retailers.

The findings reveal how major retailers’ decisions about tobacco sales can affect community health, both positively and negatively.