Latino high school students are standing out from the crowd and for all the wrong reasons—bucking a national trend, the percentage of Latino high school students who are heavy smokers has more than doubled in 10 years, according to a study published in the American Journal of Preventative Medicine and reported by Reuters.

The past 10 years have brought sweeping changes to the smoking landscape, with fewer cigarettes on the market, increases in price, and enforcement of stringent smoke-free policies. And those changers have decreased heaving smoking among U.S. high schoolers—except for Latino students.

For the study, researchers compiled data from 14,000 to 16,000 students who answered a national survey about their smoking and health habits. Heavy smoking was defined as smoking 11 or more cigarettes a day, moderate smoking as smoking between six and 10 cigarettes a day, and light smoking as smoking one to five cigarettes a day.

Researchers found two phenomena. First, that for all groups except Latinos heavy smoking fell from 18 percent in 1991 to 7.8 percent in 2009. In contrast, heavy smoking among Latino students doubled in that time frame, from 3.1 percent to 6.4 percent. Second, casual and occasional smoking rose from 67.2 percent to 79.4 percent.

While researchers aren’t sure what’s causing the increase among Latinos, it could be a byproduct of assimilation, said lead study author Terry Pechacek, PhD, associate director for science at the Centers for Disease Control and Prevention’s Office on Smoking and Health.

“I don’t think we fully understand that,” Pechacek said. “The U.S. Hispanic population have been lighter smokers in general, but it’s possible that as more Hispanics are moving forward in the middle class, Hispanics are becoming more like everybody else. It’s not proven, but that is something we are looking at.”

And as for the rise of occasional or light smoking among youth, Pechacek is concerned that the warning signs of smoking may go unheeded.

“It is important to note that light and intermittent smoking still has significant health risks,” Pechacek said. “We think there may be an emerging pattern. We may be creating a new type of smoker that may be more durable, that are adapting to smoke-free environments and to changing social norms.”

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