Compared to schools with mostly white students, schools with higher numbers of Hispanic, black, and low-income students are more likely to have tobacco retailers and fast-food restaurants in easy reach, researchers say.

"Schools are places where we expect to be healthy, supportive environments for kids, but right outside the door (students) could be exposed to unhealthy influences," lead author Heather D'Angelo of Westat in Rockville, Maryland told Reuters Health in a phone interview.

"I was surprised that there were so many tobacco outlets near schools," said D'Angelo, who at the time of the study was at the University of North Carolina in Chapel Hill.

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D'Angelo and her colleagues randomly selected more than 18,000 public schools in 97 U.S. counties, then analyzed their proximity to retailers within an 800-meter radius - roughly equivalent to a 10-minute walk.

They report in the American Journal of Public Health that 40 percent of the schools were near at least one fast food restaurant, 77 percent were close to at least one retailer likely to sell tobacco products, and 38 percent of schools were close to both.

Schools with higher numbers of Hispanic, black, and low-income students receiving free and reduced-price lunch were more likely to have tobacco retailers and fast-food restaurants within a ten-minute walk.

More than 50 percent of schools with a majority of Hispanic students were within 800 meters of both a tobacco outlet and a fast food outlet, compared to 21 percent of schools with a majority of white students.

When researchers took population density into account, they found that every 10 percent increase in the proportion of a school's Hispanic students was associated with a five percent higher likelihood the school was within walking distance of places to buy both tobacco and fast food.

A 10 percent increase in low-income students was associated with a three percent higher likelihood a school was near both kinds of stores.

The researchers also report that fast food and tobacco were more easily accessible for older kids, suggesting "that retailers may be well aware of and ready to take advantage of the autonomy and purchasing power of older youths."

"High schools had 40 percent more fast food restaurants and 24 percent more tobacco outlets within 800 meters than did primary schools and high schools had nearly 1.5 times greater odds of having both" nearby, they wrote.

The researchers say theirs is the first study to consider the availability of both tobacco and fast food on the basis of students' socioeconomic and racial characteristics.

The study did not analyze how students get to school, whether they leave campus during lunchtime, or where they live. Nor did the researchers have data on students' eating habits, or their weight or health status.

"This is looking at one point in time," said D'Angelo. "I can't say one thing causes another. However, there's still an association here."

She noted that since the study only looked at fast food chains, the number of restaurants serving unhealthy food in the areas studied could be even higher.

D'Angelo and her co-authors argue that while licensing or zoning policies could restrict students' exposure to tobacco and unhealthy foods, more research on neighborhood disparities is needed in order to change public policy.

"Food and tobacco habits begin at a young age, and habits tend to consolidate and 'stick' or 'track' over time," said Steven H. Kelder, an epidemiologist who was not involved with the study.

Kelder, who co-directs the Michael and Susan Dell Center for Healthy Living at the University of Texas School of Public Health in Austin, told Reuters Health by email that studies like this one provide information on how to address growing health disparities based on race and income and could point to the need for tighter restrictions at the point of sale, or counter-marketing to students of color.

"In this country we have a history of commercially taking advantage of poor, less educated, and vulnerable populations," Kelder said. "Documenting health disparities highlights the need to address uncovered problems."