by Todd Neale
Levels of tobacco-related nitrosamines — known carcinogens produced when curing tobacco — are higher in popular brands of American cigarettes compared with those from other countries, potentially leading to more cases of lung cancer, researchers found.
The study of 126 smokers in four countries found that exposure to one carcinogen — 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) — was highest among those from the U.S. compared with smokers from England, Canada, and Australia, according to David Ashley, PhD, director of office of science at the FDA’s Center for Tobacco Products, and colleagues. Ashley conducted the study while he was with the CDC National Center for Environmental Health in Atlanta.
The findings, reported in the June issue of Cancer Epidemiology, Biomarkers & Prevention, suggest that exposures to these chemicals can be reduced by changing curing practices and the blend of tobacco used during manufacturing.
The report notes that American-blend cigarettes typically contain burley tobacco, which has higher levels of tobacco-related nitrosamines, whereas cigarettes produced in the other three countries typically contain bright tobacco, which is lighter in color, flue-cured, and lower in levels of these carcinogens.
The researchers cautioned, however, that lowering levels of tobacco-related nitrosamines in American cigarettes would not necessarily make them safer because it may increase exposure to other numerous harmful chemicals found in tobacco smoke.
John Spangler, MD, MPH, of Wake Forest University Baptist Medical Center in Winston-Salem, N.C., said in an e-mail to MedPageToday that he’s concerned that lowering levels of tobacco-related nitrosamines could also lead to a public perception that switching cigarette brands might improve health outcomes.
He also cautioned that this study looked only at two cancer-causing chemicals in cigarettes.
“It did not look at the two dozen other cancer-causing toxins. And it did not examine any of the chemicals that might affect heart disease, stroke, emphysema, and many of the other diseases caused by tobacco use,” said Spangler, who noted that there are about 4,000 chemicals in tobacco smoke.
“So best case scenario is that you might reduce your risk of cancer. Maybe. But this says nothing about your risk of other tobacco-related diseases,” Spangler commented.
Ashley and his colleagues assessed differences in exposure to NNK and its major metabolite — 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) — by recruiting 126 daily smokers ages 18 to 52 from two U.S. sites — New York and Minnesota — and from one city each in Canada, England, and Australia.
All participants had smoked at least 10 cigarettes a day for the past year and had been a regular smoker of one specific brand for at least three months. Seventeen popular American brands were evaluated in the study, including Marlboro, Newport, Newport Light, Camel Light, and Marlboro Menthol.
The self-reported number of daily cigarettes smoked ranged from 15.6 in England to 19.7 in Minnesota, which was slightly higher than the actual number of butts collected over the 24-hour study period.
Scientists measured chemicals in cigarette butts collected by each smoker over a 24-hour period to determine how much of a certain tobacco-specific nitrosamine (TSNA) entered the smokers’ mouths during that period. They also collected urine samples to measure the breakdown product from this TSNA. Comparing the results from these two tests showed a correlation between the amount of one TSNA that enters the mouth and the amount of its breakdown product that appears in the urine. This is the first time this relationship has been documented.
Mouth-level exposures to NNK were highest in New York (1,490 ng/24 hrs), followed by Minnesota (1,150 ng/24 hrs), England (1,010 ng/24 hrs), Canada (449 ng/24 hrs), and Australia (350 ng/24 hrs).
Higher mouth-level exposures of NNK were associated with increased urinary levels of the metabolite NNAL (P=0.004).
The authors noted that two recent studies have found a direct association between NNAL levels in smokers and risk of lung cancer.
“This literature, combined with the findings in our current report, suggests that the higher levels of tobacco-related nitrosamines in the smoke of leading U.S. cigarette varieties lead to higher mouth-level exposure to NNK and increased NNAL in smokers, which may be associated with excess lung cancer burden among U.S. smokers,” they wrote.
The authors acknowledged some limitations of the study, including the relatively small sample size and the measurement of mouth-level exposure over 24 hours only. They also noted that “this study was not designed to evaluate every possible confounder. Other variables, such as individual metabolic rates, also could be significantly associated with the relationship between delivery of smoke emissions and biomarkers of exposure and would help in assessing the variance of exposure biomarkers to the emissions from cigarette smoke.”
Todd Neale is a MedPage Today staff writer.