Scientific Evidence Portal
Alcohol, tobacco and breast cancer - Collaborative reanalysis of individual data from 53 epidemiological studies | Collaborative Group on Hormonal Factors in Breast Cancer
Article Published: 2002
Published By: British Journal of Cancer (2002) 87, 1234-1245
Further Information Abstract only
"The relative risk of breast cancer increased by 7.1% (95% CI 5.5-8.7%; P<0.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1% per 10 g per day, P<0.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol."
"When analyses were restricted to 22,255 women with breast cancer and 40,832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers =1 .03, 95% CI 0.98-1.07, and for current smokers=0.99, 0.92-1.05)"
Emphases added above. This study has been called the "definitive answer" for alcohol, smoking, and breast cancer — definitive, or course, not in the scientific sense, but as far as meta-analyses of questionnaire-based epidemiological studies go. Epidemiology, by definition, cannot establish causation because it is not science, but just reflects the opinions of individuals who guess with more or less bias on the undemonstrated "causation." Unfortunately, too often their guesses are represented as science that demonstrates causality, using the mechanism of "consensus," which in turn is misleadingly portrayed as "scientific proof."
Those limits apply universally to multifactorial epidemiology. The statement of Sir Richard Doll, a co-author of this study, must be interpreted within those limits: "For the first time we have undertaken a study large enough and detailed enough to look at the separate effects of tobacco and alcohol reliably. When we did this we found that drinking, but not smoking, increases the risk of breast cancer."