Alcohol Intake Lowers Risk of Heart Disease But … Increases Risk of Breast Cancer?

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A study published this week in the Journal of the American Medical Association suggests that even moderate alcohol consumption — as little as one-half to one drink per day — increases a woman’s risk of breast cancer by about 15% [1]. Daily consumption of two or more drinks per day (where a “drink” contains about 14 grams of pure alcohol, and results are independent of the type of drink consumed) increases breast cancer risk by 50%. These results suggest a much stronger effect of low to moderate alcohol consumption on lifetime breast cancer risk than previous studies [2-4] have done.

One of the major differences between this most recent study and previous analyses of the relationship between alcohol and breast cancer is that the new study was very high-power, meaning that the number of participants was quite large (nearly 75,000 women). The sheer number of study subjects allowed researchers to determine the relationship between low-level drinking and cancer risk with much higher confidence than previous studies, with their fewer participants, had allowed. Another strength of the new study is that it was longitudinal, taking place over 28 years. However, the participants were not assigned to treatment conditions, and the researchers relied upon self-report to track alcohol consumption. Both of these somewhat weaken the results of the study, though in largely unavoidable ways. Self-report relies upon participants to accurately report their alcohol consumption, and can result in inaccurate data if participants misremember or misrepresent their drinking. Further, study results are generally more powerful and more easily generalized to the population if participants are assigned randomly to conditions. Assigning participants helps to remove confounding factors that could partially or fully explain the results. For instance, the researchers reported that the majority of women who drank a moderate amount of alcohol on a regular basis had lower BMI, were more likely to have had natural menopause, and were more likely to be smokers.

Any one of these factors might have impacted breast cancer risk (smoking is the one with the most obvious plausible mechanism), or an unidentified third variable that occurred more commonly among low to moderate drinkers could have increased risk of breast cancer.

The results of the JAMA study are interesting, and certainly support the results of many other studies: cancer risk increases with increasing alcohol consumption. However, the results of this study aren’t necessarily reason in and of themselves to cease all alcohol consumption. Studies also suggest that low to moderate alcohol consumption (about 1-2 drinks per day for men, and one drink per day for women) increases HDL and decreases risk of cardiovascular disease, heart attack and stroke [5,6]. This is because regular, limited amounts of alcohol prevent the buildup of smooth muscle cells in blood vessels that leads to the narrowing of the arteries.

While breast cancer certainly gets more media attention than heart disease, especially where it comes to women’s health, the U.S. Centers for Disease Control and Prevention (CDC) report that heart disease is the number one cause of death in women, resulting in more than a quarter of all female deaths. In an article written for the journal Circulation, Dr. Rose Marie Robertson discusses the misperceptions that so many women have about the relative dangers of health threats [7]. She notes that the vast majority of women believe cancer is their greatest health threat, while fewer than 10% recognize heart disease as such.

Therefore, while few doctors would recommend introducing alcohol for the sole purpose of lowering the risk of heart disease (since alcohol consumption is associated with a number of negative health effects), it would be shortsighted to cease moderate alcohol consumption for the purpose of preventing breast cancer, given its positive impact on the heart. To their credit, the authors of the new JAMA study recognize this, and advise women to talk to their doctors about alcohol, breast cancer, and heart disease.

References

1. Chen et al. Moderate Alcohol Consumption During Adult Life, Drinking Patterns, and Breast Cancer Risk. JAMA. 2011 Nov 2;306(17):1884-1890.
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2. Smith-Warner et al. Alcohol and breast cancer in women: a pooled analy- sis of cohort studies. JAMA. 1998 Feb 18;279(7):535-40.
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3. Dumeaux et al. Useoforalcon- traceptives, alcohol, and risk for invasive breast cancer. Cancer Epidemiol Biomarkers Prev. 2004 Aug;13(8):1302-7.
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4. Longnecker et al. Risk of breast cancer in relation to lifetime alcohol consumption. J Natl Cancer Inst. 1995 Jun 21;87(12):923-9.
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5. Ronksley et al. Association of alcohol consumption with selected cardiovascular disease outcomes: a systematic review and meta-analysis. BMJ. 2011 Feb 22;342:d671. doi: 10.1136/bmj.d671.
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6. De Oliveira E Silva et al. Alcohol consumption raises HDL cholesterol levels by increasing the transport rate of apolipoproteins A-I and A-II. Circulation. 2000 Nov 7;102(19):2347-52.
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7. Robertson RM. Women and cardiovascular disease: the risks of misperception and the need for action. Circulation. 2001 May 15;103(19):2318-20.
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