As few as 3-6 drinks a week increase breast cancer risk
Alcohol is known to be a risk factor in the development of breast cancer. Nevertheless, the precise nature of this risk is unknown. This study, published in JAMA, assessed the importance of dose, binge drinking and age. (1)
It used the results of a large prospective cohort study, the Nurses Health Study, which collected questionnaires from NHS nurses and followed them up from 1980 to 2008. In the cohort of 74,854 women, 7,960 breast cancers occurred. The alcohol intake was checked against more detailed food diaries, and breast cancer diagnosis confirmed via pathology reports. A multivariate analysis was used to control for the other factors associated with breast cancer, including cigarette smoking, family history, body mass index, age at menarche, parity, age at first pregnancy, breast-feeding and menopausal status.
The results show that increasing alcohol intake was correlated with an increasing risk of invasive breast cancer. Even moderate doses of alcohol, 3-6 drinks a week or about 4-9 units, were statistically significant (relative risk 1.15, 95% CI 1.06-1.24). There was a weak association with binge drinking, which was defined as consuming 4 or more drinks at one time. Drinking at a young age (18-40) and at an older age (above 40) were independently associated with increased breast cancer risk. Individuals with a high average alcohol intake over all the study time had the highest risk.
These results came from an observational study, so there could be confounding factors although the authors controlled for the important, known risk factors. This research highlights the importance of alcohol as a risk factor in invasive breast cancer, and potential to decrease breast cancer incidence through abstinence. However, as the article suggests, this increased risk needs to be balanced with the cardioprotective effects of moderate alcohol consumption.