(CNN) -- Black smokers have higher levels of nicotine in their bloodstreams than white smokers, which may account for higher rates of tobacco-related diseases in blacks, researchers reported Tuesday.

"African-American smokers are less likely to quit smoking than white smokers and also African Americans are more likely to develop and die from lung cancer than whites," said the leader of the study, Dr. Ralph Caraballo of the Centers for Disease Control and Prevention in Atlanta.

The research, published in this week's Journal of The American Medical Association, found that although blacks smoke, on average, fewer cigarettes than whites, their blood levels of cotinine, a metabolized form of nicotine, were higher.

CDC researchers said there is no clear reason for the difference. It could be related to smoking habits or biological differences in the way blacks and whites process nicotine in their bodies.

Research showing higher retention of nicotine could help explain the lower rate of blacks who quit smoking.

In a separate study in the same journal, researchers from the University of California in San Francisco found that black smokers retained nicotine and cotinine longer that white smokers when the chemicals were given intravenously.

The studies come at a time when the fastest growing population of new young smokers is young black Americans.

Reporter Louise Schiavone and Reuters contributed to this report.