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Study finds low levels of alcohol may be associated with increased risk of breast cancer

Nov. 1, 2011

By Maria Serraino

Consumption of three to six alcoholic drinks per week may be associated with a small increase in the risk of breast cancer, according to a recent study.

Wendy Y. Chen of Brigham and Women’s Hospital and Harvard Medical School and her colleagues examined the association of breast cancer with alcohol consumption during adult life, including quantity, frequency and age at consumption. Multiple studies have previously linked alcohol consumption to breast cancer risk, but the risk of lower levels of consumptions, role of drinking patterns and consumptions at differences periods of life, are not well understood.

The study included 105,986 women (aged 30 to 55) enrolled in the Nurses’ Health Study (NHS) who were followed from 1980 until 2008. They completed an early adult alcohol assessment at the beginning of the study, and eight updated assessments. The primary outcome the researchers measured was the risk of developing invasive breast cancer.

From 1980 until June 2008, there were 7,690 cases of invasive breast cancer diagnosed among the participants. Analyses of data indicated that a low level of alcohol consumption (5.0 to 9.9 grams per day, equivalent to three to six glasses of wine per week) may be associated with a modest increase in risk by 15 per cent. Women who consumed at least 30 grams of alcohol daily on average (at least two drinks per day) had a 51 per cent increased risk of breast cancer, compared with women who never consumed alcohol.  The study found that there was a one per cent increase in risk with each 10 grams of alcohol intake per day.  

The researchers found that when examined separately, alcohol consumption levels at ages 18 to 40 years and after age 40 were both strongly associated with breast cancer risk. The association with drinking in early adult life still persisted even after controlling for alcohol intake after age 40. Binge drinking, but not frequency of drinking, was modestly associated with breast cancer risk.

The study examined associations with alcohol consumption at different periods of life. For this analysis, followup began with the 1988 questionnaire with questions about alcohol consumption at ages 18 to 22, 25 to 30, and 35 to 40. Based on these answers, the researchers calculated the cumulative average intake between the ages of 18 and 40 as a representation of drinking during early adult life, and cumulative intake after age 40 years as representation of drinking later in life. 

Although the exact mechanism for the association between alcohol consumption and breast cancer is not yet known, one probable explanation that the study explains involves alcohol’s effects on circulating estrogen levels.

This study highlights the importance of considering a woman’s total exposure to alcohol over her lifetime as the best measure, rather than exposure during one specific time period. It suggests that to make the best personal choice regarding alcohol consumption, individuals will need to weigh the modest increased risks of breast cancer development associated with light to moderate alcohol use against its beneficial effects on cardiovascular disease. 

In an editorial accompanying the study, Dr. Steven Narod, director of the Familial Breast Cancer Research Unit at Women’s College Research Institute, explains that the association between alcohol use and increased risk of breast cancer is not a novel finding, but that the study provides more detail about the risks associated with different patterns of consumption.  According to Dr. Narod, most women start drinking at an age when their breast cancer risk is low, and few women stop drinking as adults. What is not known is how it would affect breast cancer risk if a woman started drinking – or gave up drinking – at age 50.   

Dr.  Narod says that the findings raise an important clinical question of whether postmenopausal women should stop drinking to reduce their risk of breast cancer. For some women the increase in risk of breast cancer may be considered so substantial that quitting would be the obvious choice. However, there are no data to provide assurance that giving up alcohol will reduce breast cancer risk.

“We can’t say with certainty that if a woman stops drinking now at the age of 60, after having been drinking for 40 years, that her risk of breast cancer will decrease,” says Dr. Narod.  

Moreover, he explains that it would likely be easier for a woman who consumes one drink a week to stop drinking than for a woman who consumes two drinks per day. Further, women who abstain from all alcohol may find that the potential benefit of lower breast cancer risk is more than offset by the benefits that have been associated with the occasional glass of red wine. 

“It’s important to remember that there are many health benefits associated with consuming small amounts of alcohol, like red wine, especially in terms of cardiovascular disease,” he explains.  He suggests that further studies should be conducted exploring the risk-benefit of alcohol use. 

The study and the editorial appear in the Nov. 2, 2011 issue of JAMA.

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