Moderate Drinking Over A Woman’s Lifetime Linked to Breast Cancer Risk

A new study has found that cumulative alcohol consumption in women is a risk factor for breast cancer. Even low levels of drinking were found to be linked to a small increase in breast cancer risk according to research published in today’s issue of the Journal of the American Medical Association (JAMA) (Chen et al. JAMA, November 2, 2011-Vol 306, No. 17) by Wendy Chen at DCFI in Boston, MA and colleagues. The study results showed that both earlier in life higher alcohol consumption episodes and later adult drinking were associated with a risk for breast cancer development.

The percent attributable risk (PAR) for each category of alcohol consumption was 1% to 3%, quite low due to the low numbers of participants with higher levels of consumed drinks. The overall PAR for alcohol consumption was 10%. With each 10 grams of alcohol per day (3 to 6 drinks), a 10% increase in risk was observed. No difference in risk was found from consumption of different types of alcohol.

Alcohol consumption between the ages of 18 and 40 and after age 40 were independently and both strongly associated with breast cancer risk. Alcohol consumption was “more strongly associated” with estrogen-receptor (ER)-positive, progesterone receptor (PR)-positive status, or both, although the association was not statistically significant. The link may be due to the effect of alcohol on circulating estrogen levels.

“Even moderate levels of alcohol consumption may be associated with a small increase in breast cancer risk, but the most important measure is what the average intake was over this long period of time” said Dr. Chen.

The effect of drinking patterns such as frequency, binge drinking, and higher levels during younger adulthood are not understood mostly due to a lack of significant long-term data. Many previous studies did not track alcohol consumption throughout a woman’s lifetime, which is likely very important data for making a proper assessment of risk. 

The observational study of 105,986 women followed for the women for 28 years. It started in 1980 and end in 2008. and included an early adulthood assessment followed by eight additional follow-ups. Increased drinking was associated with a statistically significant increased risk of breast cancer (1.15 relative risk, 333 cases per 100,000 person-years). The risk was present with a moderate level of drinking, approximately 3 to 6 drinks per week.

Part of the importance of the quantification aspect of the study is that the definition of moderate drinking is fairly vague.  According to the Dietary Guidelines for Americans, moderate drinking is defined as having no more than one drink per day for a woman. However, this definition refers to the amount of alcohol consumed on any single day and does not necessarily mean that moderate drinking refers to having 7 drinks on average per week. Binge drinking or heavy episodes of drinking for women is roughly defined as four or more drinks at one given time.

Binge drinking, but not the frequency of drinking was associated with breast cancer risk in the study. This was the result after controlling for cumulative alcohol intake. Women who consumed at least two drinks per day had a greater risk of breast cancer (1.51 relative risk, 413/100,000 person-years).

According to analysis of two previous national surveys on adult alcohol consumption conducted from 1992 until 2002 by researchers from the University of Texas School of Public Health and the University of North Texas Health Science Center, more adults in the U.S. are drinking alcohol, consistently across both genders and across ethnic groups. The average number of drinks consumed per month by individuals has remained steady, according to the analysis. The study also found an increase in the number of people that binge drink at least once a month. On average, the study showed that white, black, and Hispanic women consumed 6, 5, and 3.5 drinks per month, respectively. Approximately 47% of white women, 32% of Hispanic, and 30% of black women consume alcohol.

The current JAMA study used the Nurses’ Health Study, a population that reflects the demographic of nurses in the United States in 1976, with 93.7% white participants, 2% black, 0.7% Asian, and 3.6% other or unknown ethnicity. During the duration of the study follow-up, 7,690 cases of invasive breast cancer were diagnosed among the study cohort.

According to the authors, this is the first study to evaluate breast cancer risk with respect to both frequency of drinking and binge drinking. This study builds on the knowledge of the effect of alcohol on breast cancer development, however, much more research is needed to understand both the underlying mechanisms of alcohol on breast cancer development as well as underlying risk factors that may facilitate cancer onset in women who consume alcohol.