A Canadian study published in the International Journal of Cancer claims that women who smoke, or who have long-term exposure to secondhand smoke, have more than twice the risk of developing breast cancer in their childbearing years. Although a link between smoking and premenopausal breast cancer has been debated for some time, the data gathered in this study strongly supports the existence of such a connection. The findings with respect to secondhand smoke exposure were surprising but the researchers speculate that the toxins in cigarette smoke influence estrogen levels.
Previous research already suggests smoking and exposure to secondhand smoke affect the female reproductive system, significantly increase the risk of miscarriage, and cause early onset of menopause. This study, headed by Dr. Kenneth Johnson of the Public Health Agency of Canada, compiled the research from 20 previous studies.
Only last year, the International Agency for Research on Cancer (the cancer research arm of the World Health Organization) declared secondhand smoke to be a carcinogen that increases the risk of more than a dozen types of cancer. The agency claimed, however, that insufficient evidence existed with respect to breast cancer.