March 1, 2011 -- A new study shows a significant association between smoking and an increased risk of breast cancer.
The study is published in the journal BMJ.
Adding to a decade’s worth of research supporting that link, the study shows that both smokers and former smokers are at significant risk of developing breast cancer.
The researchers also report a tentative link between breast cancer and exposure to secondhand tobacco smoke.
“Since 2002, important studies with huge numbers of women have been showing a strong link,” says study co-researcher Karen Margolis, MD, a senior clinical investigator at HealthPartners Research Foundation in Minneapolis. “This adds to the weight of the evidence.”
The study, led by Juhua Luo, PhD, of West Virginia University, drew upon the Women’s Health Initiative Observational Study, which was conducted between 1993 and 1998. Researchers analyzed data on nearly 80,000 women ages 50 to 79.
The participants came from diverse backgrounds and from all over the U.S., says Margolis. During the 10 years that the participants were followed, 3,520 of them were diagnosed with invasive breast cancer.
Each study participant identified herself as a smoker, former smoker, or lifelong nonsmoker. The smokers and former smokers also answered questions about their smoking history: how old they were when they started to smoke, how many cigarettes a day they smoked, and how long it had been since they quit, if they were not still smoking. The nonsmokers were asked about the degree to which they had been exposed to secondhand smoke over the course of their lives.
Margolis and co-researchers found that compared to nonsmokers, smokers are 16% more likely to be diagnosed with breast cancer after menopause. And the longer a woman smokes, the higher those numbers climb. Among women who began smoking at an early age, before their first pregnancy, the risk of breast cancer was as high as 21%.
For former smokers, the risk is 9% greater than for lifelong nonsmokers. And while quitting reduces the risk, the researchers report that it can take up to twenty years before their risk matches that of women who never smoked.
For Margolis, the conclusion is clear: “The link between smoking and breast cancer is ironclad.”