New details of the long-term affects of secondhand smoke are detailed in two studies in the December 2009 issue of Cancer Epidemiology, Biomarkers & Prevention (CEBP), a journal of the American Association for Cancer Research.
The December issue features a special focus on tobacco studies, including lung cancer in minorities, risk for tobacco experimentation, the impact of popular culture and the effect of alternative products, such as herbal cigarettes.
In the special edition, one study found that adults have an increased risk of developing lung cancer when exposed to secondhand cigarette smoke as children, even if they never smoke themselves.
Curtis C. Harris, MD, chief of the laboratory of Human Carcinogenesis at the National Cancer Institute and one of the study's authors, said this year alone, more than 219,000 Americans will be diagnosed with lung cancer; of those, more than 72.6 percent (159,000+) will die because of it.
“Some of those will be people who have never smoked themselves. Studies to date have shown that exposure to secondhand smoke in adulthood has detrimental health effects, but data are limited on one's risk of developing lung cancer when exposure occurs in childhood,” he said.
Harris' research is different from previous studies in that it was conducted in two independent cohorts—The NCI Maryland Lung Cancer Study and a Mayo Clinic lung cancer study— and then combined data from a molecular analysis using DNA to genotype a protein encoding gene, known as MBL2. The MBL2 gene variants allow natural [innate] immunity to occur within the body. Deficiencies of this gene have been known to affect an individual's susceptibility to autoimmune, infectious and respiratory diseases.
Harris and colleagues not only found an association between childhood exposure to secondhand tobacco smoke and an increased incidents of lung cancer in adulthood, but also that MBL2 inactivity was associated with an heightened risk among those exposed to secondhand smoking in childhood.
Similarly, another study published in the December issue found that women exposed to high quantities of secondhand smoke for long periods of time, such as in bars and restaurants, or perhaps a smoking spouse or friends, may have an increased risk to breast cancer even if they never smoke themselves.
“The question of whether exposure to side-stream (secondhand) smoke could increase breast cancer risk is one that is unresolved,” said Peggy Reynolds, Ph.D., senior research scientist at the Northern California Cancer Center's Berkeley office. “While no single epidemiologic study can answer the question, our findings suggest that cumulative high levels of exposure may contribute to breast cancer, adding to the evidence for a variety of other adverse health outcomes.”
Reynolds and colleagues examined the risk of developing breast cancer among 57,000 California women who had never smoked tobacco products, but who had a history of exposure to secondhand smoke either at home, at work or in social settings. Participants also had no history of breast cancer.
In the years since completing the questionnaire, 1,754 newly diagnosed cases of invasive breast cancer occurred.
Reynolds was interested in determining whether age at exposure, setting of exposure or amount of exposure influenced the risk of developing breast cancer.
Overall, findings showed no evidence that simple measures of secondhand smoke were associated with breast cancer risk. The risk seemed to be confined to exposures experienced during adulthood (among women aged 20 or older) and primarily among those who were postmenopausal; early-life exposures (before the age of 20) alone did not appear to increase risk.
Reynolds says women exposed to moderate to high levels for a combination of years and intensity of exposure had a “significant dose response,” meaning the risk for developing breast cancer increased as the cumulative exposure levels increased.
“We were initially surprised not to see much effect individually for exposure in household, workplace or social settings," she said. “It does make sense though, if there is an effect for higher levels of exposure, the sum of exposures across settings would be more important than only partial measures of exposure.”
From a public health point of view, these results provide additional evidence for health risks from exposure to secondhand smoke, but Reynolds suggested that more research is needed to better assess overall exposure patterns.
Sources:
Childhood Exposure to Secondhand Smoke and Functional Mannose Binding Lectin Polymorphisms Are Associated with Increased Lung Cancer Risk. Susan E. Olivo-Marston, Ping Yang, Leah E. Mechanic, Elise D. Bowman, Sharon R. Pine,Christopher A. Loffredo, Anthony J. Alberg, Neil Caporaso,Peter G. Shields,Stephen Chanock, Yanhong Wu,Ruoxiang Jiang,Julie Cunningham,Jin Jen, and Curtis C. Harris
Cancer Epidemiol Biomarkers Prev December 2009 18:3375-3383; doi:10.1158/1055-9965.EPI-09-0986.
Passive Smoking and Risk of Breast Cancer in the California Teachers Study
Peggy Reynolds,Debbie Goldberg,Susan Hurley,David O. Nelson, Joan Largent Katherine D. Henderson,and Leslie Bernstein.Cancer Epidemiol Biomarkers Prev December 2009 18:3389-3398; doi:10.1158/1055-9965.EPI-09-0936
Lynette Summerill, is an award-winning journalist who lives in Scottsdale, Arizona. In addition to writing about cancer-related issues, she writes a blog, Nonsmoking Nation, which follows global tobacco news and events.