Researchers Study Nicotine Metabolism
WASHINGTON â€“â€“ Chinese-American smokers absorb less nicotine per cigarette but retain the addictive chemical longer in the blood, which may explain why they smoke less and have less lung cancer than white Americans, according to a new study.
The study analyzed how the body processes nicotine and found the chemical remains in the blood longer in Chinese-American smokers than among Hispanic and Caucasian smokers. The Chinese-Americans also tended to take in less of the chemical when they smoked.
Dr. Neal L. Benowitz of the University of California, San Francisco, said this difference in nicotine metabolism may be one reason Chinese-American smokers tend to smoke fewer cigarettes per day than do white smokers. But it is not the final answer in the smoking habit differences, he cautioned, noting that Hispanic Americans smokers also tend to use fewer cigarettes.
"Part of the reason for the Chinese could be slower metabolism, which means they have to smoke less, but that doesn't explain most of the difference," Benowitz said. "Whether it is a difference in response to nicotine or if it is cultural, is just not known."
The study is part of an effort to learn why Asian smokers tend to have less lung cancer than do white or Hispanic Americans. The risk of lung cancer for Asian smokers is about four times greater than for nonsmoking Asians. However, among white and Hispanic smokers, the lung cancer risk is 10 to 20 times greater than among nonsmokers.
For African-American smokers, who were not included in this study, the lung cancer risk is even higher, 20 to 40 times greater than for nonsmokers. In 1998, Benowitz's research showed that blacks take in more nicotine than whites.
The latest research appears Tuesday in the Journal of the National Cancer Institute.
Some 37 Chinese-American, 40 Latino and 54 white smokers underwent urine and blood tests after controlled doses of nicotine to determine how their bodies process the chemical. The study also surveyed their smoking habits.
Whites tended to smoke almost twice as many cigarettes daily, an average of 20, as did the Chinese-Americans, who averaged 11, and the Latinos, who averaged 12. But the blood and urine studies showed that the Chinese-Americans tended to absorb less nicotine from each cigarette than either of the other two groups.
Benowitz said earlier studies have shown that Chinese-Americans tend to have less of a liver enzyme, called CYP2A6, that metabolizes chemicals from cigarette smoke. He said this enzyme also turns some of the chemicals into carcinogens, or cancer-causing compounds.
"We hypothesize that the reason they have lower lung cancer risk is that they activate fewer carcinogens because they have less of this enzyme in the liver," said Benowitz.
The study is "really elegant," said Rachel Tyndale, a pharmacogenetics professor at the University of Toronto who said it supports some of her previous findings that Asians are genetically prone to slower nicotine metabolism.
"It's consistent with the evidence that Asians are at lower risk for lung cancer and starts to provide some of the explanation for why," she said.
But it does not explain why the Latinos also tended to smoke less, Benowitz cautioned.
Still, research by Benowitz and Tyndale has important treatment implications, added nicotine expert K. Michael Cummings of the Roswell Park Cancer Institute. People who metabolize nicotine more quickly will need higher doses of nicotine-replacement therapy than slow metabolizers like the Chinese-Americans, he explained.