Alcohol and Breast Cancer: The Modifiable Risk Hiding in Plain Sight

Key Takeaways:

• Pooled individual data from 53 studies, including 58,515 women with breast cancer, showed breast cancer risk rising 7.1 percent for each additional 10 grams of alcohol, about one drink, consumed per day, and the increase was the same in smokers and never-smokers.
• In the Nurses’ Health Study of nearly 106,000 women, breast cancer risk was measurably higher at just 3 to 6 drinks per week, and cumulative alcohol intake across adult life was the most consistent measure of risk.
• Postmenopausal women who drink 20 grams or more of alcohol a day have higher circulating sex hormones, including estrogens, and lower sex hormone-binding globulin, while acetaldehyde, the first and most toxic product of alcohol metabolism, is a recognized cancer-causing agent.

Much of the attention during Breast Cancer Awareness Month goes to screening and treatment, which makes sense. Less of it goes to the risk factors a woman can actually change, and the link between alcohol and breast cancer may be the least discussed of them. The biology runs along two tracks. The first is hormonal. Breast tissue is exquisitely sensitive to estrogen, which drives the division of the epithelial cells lining the ducts and lobules, and every division is another opportunity for a copying error to become a mutation. Alcohol nudges that hormonal environment upward. In a pooled analysis of more than 6,000 postmenopausal women across 13 prospective studies, women who drank 20 grams or more of alcohol a day, roughly one and a half U.S. standard drinks, had higher levels of all the sex hormones measured, including estradiol, and lower levels of sex hormone-binding globulin, the protein that keeps estrogen in an inactive, bound form. The second track is chemical. The body converts ethanol to acetaldehyde, the first and most toxic product of alcohol metabolism. Acetaldehyde binds to DNA and to the proteins that repair it, and it is the focus of most research into how alcohol causes cancer. Because both tracks run through ethanol itself, the type of drink matters far less than the amount.

The epidemiology is unusually large and unusually consistent. A collaborative reanalysis gathered the original data from 53 studies, more than 80 percent of the relevant information in the world at the time, covering 58,515 women with invasive breast cancer and 95,067 women without it. Compared with non-drinkers, women drinking 35 to 44 grams a day had a 32 percent higher risk, and those drinking 45 grams or more had a 46 percent higher risk. Across the whole range, risk rose by 7.1 percent for each additional 10 grams a day, about one standard drink in many countries, and that slope was identical in ever-smokers and never-smokers, which rules out smoking as the explanation. If the relationship is causal, the authors estimated that about 4 percent of breast cancers in developed countries are attributable to alcohol. The Nurses’ Health Study then asked about lighter drinking. Following nearly 106,000 women for close to three decades, with alcohol intake updated repeatedly, it found risk was already significantly elevated at 5 to 10 grams a day, the equivalent of 3 to 6 drinks a week, with a relative risk of 1.15. Binge drinking added risk beyond total intake, and drinking both earlier and later in adult life contributed independently, which is why cumulative lifetime intake proved the most consistent measure.

How much alcohol raises breast cancer risk, and what can you do?

There is no clear threshold below which the association disappears, but it helps to keep the numbers in proportion. A relative increase of 7 percent per daily drink is modest for any one person, and most women who drink will never develop breast cancer because of it. The point is not alarm or guilt. It is that alcohol is one of the few breast cancer risk factors fully within a woman’s control, unlike age, genes, breast density, or the age of a first period, and that the risk scales with the dose. That makes small changes meaningful. Alcohol-free days during the week, a smaller pour, saving drinks for occasions rather than habit, and avoiding several drinks at a sitting all reduce cumulative exposure, and non-alcoholic alternatives have never been better. The weighing is personal. The pooled analysis itself noted that alcohol’s effect on breast cancer has to be interpreted alongside its other effects, and a woman with a strong family history of breast cancer, a known high-risk gene, or dense breast tissue has more reason to cut back than someone at average risk. What every woman deserves is the information, stated plainly: the risk begins at lower levels of drinking than most people assume, it accumulates over a lifetime, and it is one of the rare levers in breast cancer prevention that is hers to pull.

References:

1. Key, T. J., Appleby, P. N., Reeves, G. K., Roddam, A. W., Helzlsouer, K. J., Alberg, A. J., et al. (2011). Circulating sex hormones and breast cancer risk factors in postmenopausal women: Reanalysis of 13 studies. British Journal of Cancer, 105(5), 709-722.
2. Seitz, H. K., & Stickel, F. (2007). Molecular mechanisms of alcohol-mediated carcinogenesis. Nature Reviews Cancer, 7(8), 599-612.
3. Hamajima, N., Hirose, K., Tajima, K., Rohan, T., Calle, E. E., Heath, C. W., Jr., et al. (2002). Alcohol, tobacco and breast cancer: Collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 women without the disease. British Journal of Cancer, 87(11), 1234-1245.
4. Chen, W. Y., Rosner, B., Hankinson, S. E., Colditz, G. A., & Willett, W. C. (2011). Moderate alcohol consumption during adult life, drinking patterns, and breast cancer risk. JAMA, 306(17), 1884-1890.