Nicotine Studies Find Racial Factor
African American smokers have higher levels of the metabolized form of nicotine in their bodies than do white smokers, providing potential clues about why blacks are less likely to quit smoking and more likely to develop lung cancer than whites, according to a study of more than 2,000 people by federal researchers published today in the Journal of the American Medical Assn.
The findings may indicate behavioral differences in the way African Americans smoke, or biological differences in the way they metabolize the nicotine metabolite, called cotinine, said lead investigator Ralph Caraballo, an epidemiologist at the federal Centers for Disease Control and Prevention’s Office on Smoking and Health.
After controlling for variables such as body weight, age and exposure to secondhand smoke, researchers at the CDC found that African American smokers had 12% to 50% higher levels of cotinine than white smokers, and 32% to 56% higher cotinine levels than Mexican Americans.
A separate UC San Francisco study of black and white smokers in the same journal also found that black smokers absorb more nicotine per cigarette and retain more cotinine in their bodies than white smokers do.
The studies suggest that prevention and treatment strategies may need to be adapted to suit variances in ethnic and racial groups, researchers said.
“To me these studies emphasize the importance that future research does a better job in including the diverse nature of the population in the U.S.,†said Jack Henningfield, associate professor of psychiatry at Johns Hopkins University Medical School and editor of the 1988 surgeon general report on nicotine addiction.
In the CDC study, researchers analyzed blood samples from 2,136 subjects age 17 or older who had participated in the Third National Health and Nutrition Examination Survey between 1988 and 1991. All subjects had reported smoking at least one cigarette in the five days prior to the time blood samples were taken.
Previous studies had also shown ethno-racial differences in levels of cotinine between African Americans and whites, but the study by CDC researchers puts the weight of a large, population-based survey behind those earlier findings, in addition to including Mexican Americans in the analysis.
The study at UC San Francisco suggests a combination of behavioral and biological factors may be at work. In the study, 40 black and 39 white smokers in the study were given pure nicotine and cotinine intravenously. Researchers found that black subjects cleared 25% less of the cotinine from their bodies, compared to white subjects. In addition, the subjects were later allowed to smoke, and it was found that blacks took in 30% more nicotine per cigarette.
“This means black people who are smoking cigarettes are taking more puffs, more deeply,†said Dr. Neal Benowitz, chief of the Division of Clinical Pharmacology at the UC San Francisco Department of Medicine and co-author of the study. Benowitz said higher intake of nicotine may also mean greater absorption of the cancer-causing substances found in the tar and smoke of tobacco.
“That is what we think explains why black men have a higher risk of lung cancer,†Benowitz said.
In addition to having a higher lung cancer risk, African Americans who had tried to quit for at least one day were slightly more likely than whites to have relapsed to daily smoking, according to data from the National Cancer Institute.
“What these studies show is that there may be genetic variations in why people smoke and in the consequences of smoking,†said Dr. Edward Sellers, professor of pharmacology and medicine at the University of Toronto and an author of an editorial accompanying the studies. Sellers co-authored a recent study indicating that a defect in a gene, labeled CYP2A6, may cause nicotine to be broken down more quickly, leading more readily to nicotine addiction.
Cotinine has been used as a marker for tobacco use and exposure because it remains in the body up to 10 times longer than nicotine, making it easier to detect.
Sellers said that a group of enzymes, known as UGTs, responsible for detoxifying drugs in the body, may also be important in the breakdown of cotinine.
He said a closer look at the prevalence of these enzymes in various ethnic and racial groups might help illuminate some of the differences shown in the studies, though he said those studies will take years to perform.
Jennifer Unger, assistant professor of research in preventive medicine at USC, said the studies have important implications for smoking prevention programs.
“In smoking prevention research, we usually call someone an addicted smoker after they’ve smoked 100 cigarettes,†Unger said. “For blacks, they may become addicted even earlier because they get more nicotine per cigarette. This might also explain why black smokers show higher rates of tobacco-related diseases even if they smoke fewer cigarettes than white smokers do.â€
To the extent that the problem is behavioral, an obvious solution would be to target more smoking cessation programs to African American communities, experts say. As the surgeon general’s report on minority tobacco use points out, many black smokers are not getting information on cessation techniques through such programs.
Johns Hopkins’ Henningfield said: “Most tobacco research in the past has been conducted in the Caucasian population. The important issues that these studies raise is in developing preventive and treatment strategies. “We can’t assume that one size fits all.â€
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Metabolizing Nicotine
An average of 65% to 80% of the nicotine absorbed by the body is metabolized into what is called cotinine. In a new study, African American smokers have been found to have higher levels of cotinine in their blood than whites and Latinos.
Serum Cotinine Level (nanograms/milliters)
Non-Latino Blacks
Non-Latino Whites
Mexican Americans
No. of Cigarettes Smoked per Day
Source: CDC Office on Smoking and Health
