Of the top 100 universities as ranked by U.S. News and World Report, 11 allow tobacco sales and 13 allow e-cigarette sales on "campus cash" debit cards that are commonly prepaid by parents, according to a recent study from the University of Colorado.

"Parents put money on these debit cards and kids spend the money. What parents don't realize is that tobacco may be purchased with some of these college debit cards," Robert P. Dellavalle, senior author of the study and investigator at the CU Cancer Center, said in a statement.

Many colleges and universities offer prepaid debit cards linked to students' campus ID cards, that can be used either at on-campus vending areas like bookstores and cafeterias, and/or at off-campus vendors that act like preferred providers.

For the study, researchers examined online lists of on-and off-campus vendors (with phone and email follow-up as needed) to discover universities whose policies allow the sale of tobacco and e-cigarettes within the campus debit card network.

In all, 94 of the 100 surveyed universities included an ID-linked debit card program, with a total enrollment of 1,452,048 students. Previous research shows that of university students who smoke, 42 percent had used campus debit cards to purchase cigarettes.

"Cracking down on this 'campus cash' is a major opportunity for these colleges to take a step toward preventing tobacco use on their campuses," said Lindsay Boyers, the study's first author.

In addition to the direct health effects of tobacco and e-cigarette products, the researchers point out that what is sold on campuses and within the networks of campus-approved vendors can reflect what is deemed socially acceptable behavior.

"Universities shouldn't be taking debit card fees from in-network vendors selling tobacco products to their students," Dellavalle said.

The findings are detailed in the British Medical Journal: Tobacco Control.