The hazards of secondhand smoke have been known for years, says researcher Ronald Crystal, MD, chief of the division of pulmonary and critical care medicine at New York-Presbyterian/Weill Cornell Medical Center and chair of genetic medicine at Weill Cornell Medical College, New York. ''But there were never any studies that had looked at the biology, why this is the case."
His study does that, demonstrating that even the lowest levels of smoke exposure lead to genetic changes at the cellular level in the lungs. "What this study shows is, if we could detect nicotine in the urine, we could also detect changes in the number of genes turned on and off'' in the cells of the lungs, Crystal tells WebMD.
The new findings put ''scientific teeth" behind the epidemiological evidence that smoke exposure even at low levels is hazardous, says Zab Mosenifar, MD, a pulmonologist, director of the Women's Lung Institute, and executive vice-chair of the department of medicine, Cedars-Sinai Medical Center, Los Angeles, who reviewed the study findings for WebMD.
The study also suggests that those ''casual'' smokers who think smoking a few cigarettes a week is not hazardous are incorrect, according to the researchers.
Low Smoke Exposure: The Hazards
Crystal and colleagues evaluated 121 people, classifying them as nonsmokers, low-exposure smokers, or active smokers.
They categorized the people after evaluating their urine for levels of nicotine and a nicotine breakdown product, cotinine.
Next, "we took a small sample of the cells lining the airways," Crystal tells WebMD. "The cells lining the inside of your airways are called epithelial cells.'' When you puff a cigarette, he says, these are the first cells affected.
Next, Crystal's team scanned each person's entire genome to figure out which genes were activated or deactivated in the cells lining the airways.
"When exposed to smoke, the genes get turned on and off abnormally," he says. "The cell is crying out at a biological level, saying, 'Something's wrong. I'm being stressed here.'"
About 370 different genes sense the smoke, he says, and turn off and on in the area.
Eventually, Crystal says, the genetic discoveries may help experts figure out why some people are more susceptible to the health effects of smoke exposure than others are, and to develop treatments.
''What they have shown is that these epithelial cells inside the small airways contain very sensitive genes," Mosenifar says.
"These cells, they have these antennae, they pick up very low levels of tobacco. Small airway epithelium is very sensitive," he says."This says basically even a small amount of exposure to smoke does create changes at the cellular level in genetically susceptible people."