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Secondhand Smoke Includes Carcinogens

Passive Smoke Can Increase Lung Cancer Risk

December 19, 2003 -- Exposure to secondhand smoke greatly increases the risk of developing lung cancer, according to a review in the International Journal of Cancer. The researchers pooled the results of two large studies in the United States and Europe to try to obtain a better estimate of the role of secondhand smoke from spousal, workplace, and social sources.

The data included 1,263 lung cancer victims who had never smoked (653 from the American study and 610 from the European study) as well as 2,740 controls. Surveys and interviews included questions about the duration of tobacco exposure, the daily amount of tobacco used by household members, and the types of tobacco products. In the workplace and social situations, questions focused on the duration of tobacco exposure.

Statistics took into account the age, sex, and vegetable intake of participants and whether they were engaged in high-risk occupations linked to lung cancer. Spousal exposure to secondhand smoke was defined as having a spouse who smoked any tobacco product while the couple lived together, while smoke-years of exposure was defined as the number of years that the subject's spouse smoked while they lived together.

Years of workplace exposure was defined as the total number of years in which the subject reported working at a job where others were smoking. Smoke-years of social exposure was defined as the total number of years of exposure to tobacco smoke in places other than the home and the workplace. The researchers also calculated the sum of smoke-years from all secondary sources--spouses, the workplace, and social situations.

The pooled analysis of the two large studies provided good evidence for a dose-response relationship between lung cancer risk and duration of exposure to secondhand smoke for spousal, workplace and social exposure, the researchers concluded. For spouses who were exposed to their partner's secondhand smoke, the increased lung cancer risk was 18%. That figure increased to 23% if the secondhand smoke exposure was long-term. Secondhand smoke exposure in the workplace and in social situations also increased lung cancer risks. High-risk employment and low vegetable intake were not significant lung cancer factors in the studies.

What's in Secondhand Smoke?

The National Cancer Institute defines secondhand or passive smoke to include sidestream smoke as well as mainstream smoke. Sidestream smoke is smoke that is emitted between puffs of a cigarette, cigar, or pipe. Mainstream smoke is smoke that is exhaled by the smoker. Both sidestream and mainstream tobacco smoke contain at least 60 carcinogens, including formaldehyde, and six developmental toxic substances, including nicotine and carbon monoxide. (Environmental Tobacco Smoke, National Cancer Institute).

Secondhand Smoke: Other Studies and Health Issues

The U.S. Environmental Protection Agency and the National Institute of Health classify secondhand smoke as a carcinogen. The National Institute of Health specifically links secondhand smoke to lung cancer (Health Effects of Exposure to Environmental Tobacco Smoke). This view is echoed by the International Agency for Research on Cancer (IARC), a group within the World Health Organization. The IARC found an even higher lung cancer risk for spouses of those who smoke than did the review in the International Journal of Cancer--20% for women and 30% for men (Monograph #83, Tobacco Smoke and Involuntary Smoking). Secondhand smoke has also been associated with heart disease, asthma, and sudden infant death syndrome (SIDS).

International Support for Tobacco Review Research

The research report published in the International Journal of Cancer was supported by the U.S. National Cancer Institute, the European Commission, the Italian Association for Cancer Research, the Spanish Ministry of Health, the Swedish Environmental Protection Agency, Association pour la Recherche sur le Cancer (France), and various other European government health agencies. You can access the abstract by registering for free with the Wiley Interscience web site. The title is "Secondhand Smoke Exposure in Adulthood and Risk of Lung Cancer Among Never Smokers: A Pooled Analysis of Two Large Studies" by Paul Brennan et al. The full text is available for $25. The article was originally written in October 15, 2001, accepted for publication in September 2003, and then republished online in December 2003.

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