A new report published by the State of California finds that secondhand smoke may increase the risk of breast cancer, particularly in pre-menopausal women. The finding contradicts some previous studies which have not found an association between secondhand smoke and breast cancer, and consequently, the report's finding has become controversial. However, the researchers say that past studies have not taken into account the timing of exposure to secondhand smoke, which appears most harmful in younger women.

The report, Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant, was published by the State of California's Air Resources Board in March 2005. Findings are based on analysis of more than 1,000 studies of secondhand smoke and several health conditions.

According to the report, secondhand smoke is responsible for about 67,700 deaths each year in the United States. However, a survey developed by the California Department of Health Services finds that smoking has decreased in the state of California over the past decade, as well as in the United States as a whole.

Source: Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant, State of California, March 2005

The finding that secondhand smoke increases breast cancer risk is controversial and has already started a debate in California. According to the report, pre-menopausal women exposed to secondhand smoke may have twice the risk of breast cancer compared to other women. This finding has sparked a debate over whether smoking should be banned in vehicles because of the risk to passengers, particularly children.

The report's finding contradicts some previous studies, which have not found a link between secondhand smoke and breast cancer deaths. For example, in the largest studies of its kind, published in 2000, researchers found no association. Using data from the American Cancer Society Prevention Study II, the researchers of the 2000 study followed 146,488 non-smoking, married women who were healthy when they enrolled in the study in 1982. After 12 years, there were 669 cases of breast cancer among the women. The researchers found no difference in the death rate from breast cancer among the women whose husbands smoked versus the women who were married to non-smokers. Taking into account the women's exposure to environmental tobacco smoke at home and work, the researchers concluded that there was no link between second-hand smoke and breast cancer deaths. While some other studies have found a link between secondhand smoke and breast cancer, there were more participants in this study than in all of the previous studies on this topic combined.

The report also found that secondhand smoke can increase the risk of several other illnesses, including lung cancer, childhood asthma, and lower respiratory tract infections. The researchers found that secondhand smoke has particularly negative effects on the health of children, has a number of serious impacts on children's health including sudden infant death syndrome (SIDS), exacerbation of asthma, increased respiratory tract infections, increased middle ear infections, and causes developmental toxicity resulting in low birth weight, and impaired lung function growth, and other developmental impacts.

While the researchers did not find conclusive evidence that secondhand smoke causes other conditions, they did find some evidence to suggest that it may increase the risk for illnesses and conditions including spontaneous abortion, cervical cancer, and chronic respiratory symptoms in adults. Further research is needed in these areas.

While the link between secondhand smoke and breast cancer will likely remain controversial, several other factors have been more definitely associated with an increased risk of breast cancer. These include advancing age, mutations of certain genes (BRCA1, BRCA2), personal or family history of breast cancer, previous breast biopsy showing certain pre-cancerous conditions, early menstruation (before age 12), or late menopause (after age 50), and long-term use of hormone replacement therapy. Please see http://www.imaginis.com/breasthealth/bc_risks.asp for more information breast cancer risk factors.

Additional Resources and References

• The California Air Resources Board's report, Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant, was published in March 2005, http://www.arb.ca.gov/homepage.htm
• The October 2000 Imaginis report, Study Finds No Link Between Second-Hand Smoke and Breast Cancer Deaths," is available at http://www.imaginis.com/breasthealth/news/news10.22.00.asp

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