Black U.S. teenagers get a much bigger hit of addictive nicotine from a cigarette than do their white classmates, researchers said on Friday.

This may explain why black youths smoke fewer cigarettes, on average, than white teens but suggests smoking may be more dangerous for them, the team at the National Institute on Drug Abuse said.

“Previous research in adults showed that black smokers take in 30 percent more nicotine per cigarette and take longer to rid their bodies of the drug, compared to white smokers,” NIDA Dr. Nora Volkow said in a statement.

“The current findings, among the first on adolescent nicotine metabolism, reveal that these differences are in effect during the teen years, as well.”

Writing in the journal Ethnicity and Disease, Dr. Eric Moolchan of NIDA’s Teen Tobacco Addiction Research Clinic in Baltimore, Maryland, said they tested the blood of 61 white and 30 black adolescent smokers.

The black smokers seemed to more slowly metabolize, or break down, the nicotine from the cigarettes, leaving more of it in their blood than in young white smokers, the researchers found. The study was not designed to find out how or why this might happen.

Although black teens smoked only 15 cigarettes per day on average compared to nearly 20 a day for the whites, the blacks had more of a chemical in their blood called cotinine. Cotinine is produced when the body breaks down nicotine and the finding confirmed their bodies clear nicotine more slowly, the researchers said.

“Our findings support the hypothesis that racial and ethnic differences in nicotine metabolism exist among adolescent smokers, with black teens smoking less but being exposed to as much nicotine as white teens,” Moolchan said.

“These findings may constitute a strong warning to black youth to keep from smoking in the first place,” Volkow said.

“They also may explain why certain smoking cessation therapies work better in some populations than in others and, therefore, which treatments should be offered to which teens.”