Estrogen can fuel cancer growth, and researchers believe that smoking has anti-estrogenic effect in women, lowering the amount or activity of the hormone. Consistent with that belief is the study's finding that smoking after menopause -- when hormone levels dip dramatically -- may be associated with a slightly decreased risk of breast cancer.
"Postmenopausal women in particular have an increased risk of cardiovascular disease," Michels said. "If she adds smoking on top of that, I think it's bad. This is definitely not a license to smoke."
Dr. Mary B. Daly, director of cancer prevention and control at Fox Chase Cancer Center in Philadelphia, praised the study for using a longstanding, large number of participants.
"The study is done very carefully," Daly said. "It's an interesting field because, as the authors point out, the data so far have been conflicting."
Women's breasts are more sensitive to carcinogens before experiencing a full-term pregnancy, Daly noted, making smoking potentially more dangerous for them than for pre-menopausal women who have given birth.
"The good thing about this study is that it's not going to change anything we're going to say to people about smoking," Daly said. "In terms of public health recommendations, you still want to give the message that smoking is not healthy."
To learn more about breast cancer, visit Breastcancer.org.
SOURCES: Karin Michels, Ph.D., associate professor of obstetrics/gynecology, Brigham and Women's Hospital, Boston; Mary B. Daly, M.D., Ph.D., director of cancer prevention and control, Fox Chase Cancer Center, Philadelphia, Pa.; Jan. 24, 2011 Archives of Internal Medicine
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