Even low levels of alcohol consumption – as little as 3-6 glasses of wine per week – increase the risk of developing breast cancer, according to a report in the Nov. 2 issue of JAMA.
"Prior studies have consistently demonstrated a linear dose-response relationship between alcohol consumption and breast cancer risk, with an increased risk mainly observed among women who consumed the equivalent of at least one alcoholic beverage daily, but power was limited at the lower levels of alcohol consumption to determine whether there was a lower threshold. Our data demonstrate that even consumption of alcohol as low as 5-9.9 g per day ... may be associated with a modest increase in risk," said Dr. Wendy Y. Chen of Brigham and Women’s Hospital and Harvard Medical School, Boston, and her associates.
They analyzed data from the Nurses’ Health Study to assess the role of alcohol in breast cancer risk. The NHS involved female registered nurses who were aged 30-55 years at the study’s inception in 1976. The nurses were sent follow-up questionnaires every 2 years to update risk factor information and the development of disease. The study population was predominantly white (93.7% white, 2% black, 0.7% Asian, and 3.6% other or unknown ethnicity).
For this study, Dr. Chen and her colleagues analyzed data beginning in 1980, when alcohol intake was first assessed, and ending in 2008. The 74,854 subjects provided information on both their past and current drinking patterns.
A total of 7,690 cases of invasive breast cancer were diagnosed in these subjects during the study period.
Compared with women who did not drink alcohol, those who drank even a small amount showed a modestly but significantly increased risk of breast cancer, with a relative risk of 1.15. The risk rose as alcohol consumption increased, so women who drank at least 30 g of alcohol daily (the equivalent of two drinks per day) had a relative risk of 1.51.
"We observed a 10% increase in risk with each 10 g per day of alcohol intake," the investigators said (JAMA 2011;306:1884-90).
Both drinking during young adulthood and drinking later in life were independently associated with breast cancer risk, and the cumulative average alcohol consumption over a long period of time was the measure that had the strongest correlation. This highlights the importance of the totality of a woman’s exposure to alcohol throughout her lifetime rather than during a specific period, the researchers noted.
"We did not find any difference by type of alcoholic beverage (i.e., beer, wine, or liquor)," they added.
The tumor’s estrogen-receptor status also did not influence the association between alcohol intake and breast cancer risk, and neither did ductal or lobular histology.
The exact mechanism by which alcohol raises breast cancer risk is not yet known, but it is "probable" that its effect on circulating estrogen levels plays a role. Alcohol could raise these levels in both premenopausal and postmenopausal women by increasing aromatase activity, decreasing hepatic catabolism of androgens, or affecting adrenal steroid production. It may also increase breast tissue’s sensitivity to estrogens, Dr. Chen and her associates said.
The study was limited in that subjects were predominantly white. However, "the limited available data suggest that the association between alcohol use and breast cancer does not differ by ethnicity," they noted.
Given the study findings, every patient "will need to weigh the modest risk of light to moderate alcohol use on breast cancer development against the beneficial effects on cardiovascular disease to make the best personal choice regarding alcohol consumption."
This study was supported by the National Institutes of Health. Dr. Chen and her associates did not report any relevant financial disclosures.