What evidence links alcohol consumption to breast cancer?

Overall, most authoritative reviews and meta-analytic studies support the assertion that alcohol consumption is causally related to breast cancer, and many studies support a dose-response based upon increments of 10 grams/alcohol per day. A standard drink (12 ounces of beer, 5 ounces of wine, or one shot of liquor) has approximately 14 grams of alcohol.[1]

 

Major reports by the Interagency Breast Cancer and Environmental Research Coordinating Committee (IBCERCC)[2] and the Institute of Medicine (IOM)[3] listed alcohol as a known risk factor for breast cancer, and the IOM indicated that alcohol has one of the clearest relationships to the disease.

 

Several reports have estimated the attributable risk for developing or dying from breast cancer as a result of alcohol consumption. Figures vary considerably, depending on models used, populations studied, and number of other potential risks factored into the model. Most drastic is an analysis of the global attributable risk for breast cancer associated disability adjusted life years (DALYs: the total functional years lost across the globe) as a consequence of alcohol consumption based on 18 years of data from 195 countries and territories. This analysis estimated 9.43 % of female breast cancer related DALYs was attributable to alcohol consumption, while over 20% of male breast cancer DALYs was attributed to alcohol consumption.[4]

 

A systematic review of the literature from several northern hemispheric regions of the world concluded that approximately 13% of breast cancer cases diagnosed in North America could be attributed to alcohol consumption, while the estimates for Europe and Asia were, respectively, 20.6% and 11.5%.[5]

 

Looking at attributable risk for developing breast cancer in Australian women, alcohol consumption was estimated to be causally linked to disease development in 12.6% of premenopausal cases and 6.6% of postmenopausal breast cancers.[6]

 

A U.S. study of women under age 65 with private insurance or Medicaid, found that 12.3% of breast cancer cases among women aged 18-44 and 7.1% of breast cancer cases among women aged 45-64 could be attributed to alcohol consumption, and that $148.4 million in estimated medical costs are attributable to alcohol related breast cancers.[7] Another study estimated that 4.9% of breast cancers could be avoided if alcohol consumption were eliminated completely.[8] Results from the Nurses’ Health Study indicated that attributable risk increased as the quantity of alcohol consumed increased.[9]

 

The American Institute of Cancer Research’s continuous update project reported that consuming alcoholic drinks probably increases risk of pre-menopausal breast cancer and that the evidence is convincing that alcohol consumption increases risk of post-menopausal breast cancer. In both pre- and post-menopausal breast cancer, the relationship between alcohol consumption was dose dependent. For each 10 grams of ethanol consumption per day, pre-menopausal risk increased by 5% and for post-menopausal breast cancer, risk of both ER+/PR+ and ER+/PR- breast cancer increased by 9%.[10]

 

Several older (before 2009) meta-analytic studies show that the overall data across studies confirms a link between breast cancer and alcohol consumption. These analyses found increased risk of 22% comparing drinkers and non-drinkers,[11] a 27% higher risk of ER+ breast cancer and 14% higher risk of ER- breast cancer when comparing those with the highest levels of consumption with those with lowest consumption.[12]

 

Furthermore, these earlier meta-analyses suggested a dose-response with 7-10% increased risk per 10 grams per day of alcohol consumption,[5],[13] with evidence of increased risk of both ER+ breast cancer (approximately 12% higher risk) and ER- breast cancer (approximately 7% higher risk) per 10 grams alcohol/day.[6]

 

A 2003 review estimated that 8% of breast cancer cases could be attributed to alcohol consumption.[14] A 2017 updated review by the same authors noted that the International Agency for Research on Cancer (IARC) found sufficient animal and epidemiological evidence to conclude that alcohol is causally related to breast cancer.[15] The IARC Monographs in both 2010 and 2012 offer detailed reviews of the literature to date regarding alcohol and breast cancer. They conclude that alcohol is causally related to female breast cancer but that the data on male breast cancer is inconclusive.[16],[17]

 

Several meta-analyses and reviews since 2012 confirm the conclusions of the earlier reports. A 2015 meta-analysis of 16 studies found 28% higher risk among those with the highest consumption, when compared to the lowest consumption.[18]

 

A 2015 meta-analysis included 38 studies that specifically separated out people who never drank (abstainers) from occasional drinkers (which some other studies classified as abstainers), low-level, and high-level drinkers. They found 3% higher risk among occasional drinkers (<10g/week), 8% higher risk among low-level drinkers (<21g/day), 37% increased risk among hazardous-level drinkers (21-40g/day), and 34% higher risk among harmful-level drinkers (>40g/day), compared to abstainers.[19]

 

Several studies have included alcohol consumption as part of a healthy lifestyle index that includes other indicators, such as diet, smoking, physical activity, and body weight/BMI. In these studies, lower consumption of alcohol is considered healthier. These studies generally find that adherence to the index is protective and non-adherence increases breast cancer risk, regardless of the specific factors included in the index.[20],[21],[22],[23] When these studies look specifically at alcohol consumption, controlling for the other factors, risk still appears to be increased. One study found 17% higher breast cancer rates among women who consumed more than 19.9 grams of alcohol/day.[15] Another study found alcohol intake in the range of 15-30 grams/day was associated with 79% higher breast cancer risk, compared to non-drinkers.[24]

 

A couple of studies in 2019 and 2020 that examined alcohol consumption along with a number of other lifestyle factors found that regular alcohol consumption was associated with increased risk for developing breast cancer in both premenopausal and postmenopausal women.[25],[26],[27] A study of Japanese women found no relationship between alcohol consumption and either overall breast cancer rates or hormone receptor consistent (ER+/PR+ or ER-/PR-) cancers. A significant relationship between the amount of alcohol consumed and mixed receptor type (ER+/PR- or ER-/PR+) was found for premenopausal women.[28]

 

Cigarette smoking and alcohol consumption have each been shown to increase risk for developing breast cancer. In a long-term study of Danish nurses, the two together led to an even greater risk of developing the disease.[29] Another study examining the possible interaction of alcohol consumption and smoking on breast cancer risk found a “U-shaped” response: Moderate alcohol intake and minimal smoking were associated with a decrease in breast cancer risk, while both high alcohol and cigarette use was associated with a greatly increased risk for breast cancer.[30]

 

Research globally is less consistent. This may be due to variations in study quality, although nearly all recent studies adjusted models are based upon similar risk factors. These variations may also be due to different common patterns of drinking globally, other cultural factors, and genetics that are not captured via the common covariates.

 

Among women in Brazil, risk was almost five times higher among women under 50 who had consumed alcohol and nearly four times higher among women over 50.[31] In Italy, a study of alcohol consumption of more than 10 grams/day was associated with 30% higher risk of breast cancer.[32] A study of South Korean women found that ever consuming alcohol was associated with 19% higher risk of invasive breast cancer.[33]

 

A study from Japan found no effect for any alcohol-related factors.[34] In Southern Australia, researchers found correlations between alcohol consumption and breast cancer in a population-based study, but odds ratios were not elevated in a case-control study at any age.[35]

 

Patterns of Drinking and Types of Alcoholic Beverages

Meta-analyses of light drinking also suggest increased risk. Pooled data from 110 studies of light drinking suggests 5% higher risk overall. Among studies from North America, estimates ranged from 2% to 9% higher risk.[36] A 2018 meta-analysis of 27 studies of very light (less than .5 drinks/day) and light (.5 to 1 drink/day), found 4% higher risk of breast cancer among very light drinkers, 9% higher risk among light drinkers, and 13% higher risk among moderate drinkers. This validates the idea that alcohol consumption is dose-dependent and suggests that any level of drinking may increase risk.[37]

 

In another meta-analysis of 26 studies specifically looking at wine consumption, overall risk was increased by 36% among those with the highest levels of consumption compared to the lowest. Among pre-menopausal women with the highest levels of wine consumption, risk was 79% higher, but there was no statistically higher risk among post-menopausal women. When the consumption of other alcoholic beverages was analyzed, there was no overall increased risk.[38] But another study found alcohol consumption, whether measured as total consumption or intake respectively of wine, beer or spirits, all resulted in increased risk for both ER+ and ER- breast cancer.[39]

 

A study from the United Kingdom found 27% increased risk per 10 units (standard drinks of any alcoholic beverage) of alcohol consumption per week and a linear association of nearly double risk per 10 units of consumption of spirits.[40]

 

In the Sister Study, a large U.S. cohort study of sisters of women diagnosed with breast cancer, binge drinking (defined as drinking four or more drinks at one time) was associated with 29% higher risk of breast cancer compared to low-level drinking. Among modest drinkers who binged, risk was 25% higher than low-level drinkers who never binged. Finally, blackout drinking was associated with 39% higher risk. All analyses controlled for other key risk factors.[41]

 

Alcohol dependency (defined as attendance at alcohol treatment centers) was associated with more than tripled breast cancer risk in a Danish study.[42]

 

On the other hand, in a group of both U.S. Black and White women who were participants in the Women’s CARE Study and had been diagnosed with invasive breast cancer, long-term (since adolescence) alcohol consumption was associated with a decrease in breast-cancer specific mortality.  Death due to breast cancer in this group was also decreased in women who averaged more than one drink a day over the 5 years prior to diagnosis of breast cancer.[43]

 

Race/Ethnicity

One study found that drinking more than 14 drinks/week was associated with 78% higher risk overall. However, among U.S. Black women only, having 14 or more drinks nearly tripled the risk of breast cancer.[14]

 

Another study sought to understand whether alcohol consumption and dietary factors partially explained racial disparities in breast and other cancers. They found that, while nutrition and physical activity adherence both partly explained differences in breast cancer rates between Black and White women, alcohol did not explain the different incidence rates.[44]

 

A 2017 study looked at the association of alcohol and breast cancer risk in the AMBER Consortium, a U.S. cohort of Black women drawn from several different projects. They found 33% higher overall breast cancer risk among Black women who drank 14 or more drinks per week, compared to 0-4 drinks per week. When they looked at specific breast cancer subtypes, having more than 7 drinks/week was associated with increased risk of four subtypes: ER-, PR-, HER2- and triple-negative. Increased risk was in the range of 28-39% for all four subtypes.[45]

 

Subtypes

Several studies suggest an association between alcohol consumption and ER+ breast cancer. A study in the UK found 9% higher risk of ER+ breast cancer among drinkers, but no effect for ER- breast cancer.[46] Similarly, a Norwegian study found 14% higher risk of luminal A (ER+ and/or PR+) breast cancer among those who drank three or more glasses of wine per week. Another study found that those who drank at the time of their diagnosis were 35% more likely to be diagnosed with ER+ breast cancer than HER2+ breast cancer, and that there was no differential risk for triple-negative breast cancer.[47]

 

As noted above, in one study of Black women, alcohol consumption was associated with about 1/3 higher risk of ER-, PR-, HER2-, and triple-negative BC.[33] Due to the lack of additional studies examining disparities in subtypes of breast cancer stratified by race and ethnicity, it is not clear if different patterns would be found in different communities.

 

A large U.S. cohort study found trend effects for both invasive ductal and lobular breast cancer. Consuming more than 20 grams of alcohol per day was associated with 26% higher risk of invasive ductal cancer and 43% higher risk of invasive lobular cancer.[48] Another study found that increased alcohol consumption was associated with increased risk of developing ER+ invasive breast cancer of both ductal and lobular origins, but was also associated with a decreased incidence of ER- invasive ductal cancer.[49]

 

Nuances and Emerging Considerations

Interactions with HRT and B vitamins

There is some evidence that the effects of alcohol intake may interact with pharmaceutical hormones, and that B vitamins may ameliorate some of the risk of alcohol intake in some cases. In one study of HRT use and alcohol consumption, both increased risk independently (combined estrogen/progestin HT nearly doubled risk, estrogen alone increased risk by 40%, and alcohol consumption increased risk by 25%). Among those on HT who also consumed alcohol, risk was more than doubled.[50]

 

Intake of Vitamin B9 (folate) may be protective. Alcohol consumption as reported in 10g/day dose increments increased risk by 11% among those with low folate (vitamin B9) intake.[51]

 

Family History and BRCA Status

The effects of alcohol consumption on breast cancer risk among women with a family history of breast cancer are complicated. A study looking at familial risk profiles (based on family history of breast cancer) found that in women with relatively low risk profiles, higher alcohol intake was associated with increased risk of ER+ breast cancer. The same effect was not found for women with higher familial risk profiles, although the combination of a high-risk profile, regular alcohol consumption and smoking led to an increased risk of developing breast cancer. In another study, each 10 grams of alcohol consumed per day increased risk by 4% among those with no family history of breast cancer but increased risk by 16% among those with a family history.[39] A 2019 study of BRCA carriers found that alcohol consumption was not associated with risk among women with BRCA1 or BRCA2 mutations.[52]

 

Breast Density

Recent research has explored the relationship between alcohol consumption and mammographic breast density, an increasingly important intermediate risk factor for developing breast cancer.[53],[54] For example, one study found no relationship in breast density associated with alcohol consumption.[55] Other studies found that women who consumed alcohol were more likely to have dense breasts.[15],[56],[57]

 

Other studies have looked at whether or not alcohol effects on breast cancer risk might be associated with increased breast density and, if in turn, this relationship might be modifiable by other known risk factors for the disease. Increased alcohol consumption was associated with higher breast density, and this effect was most pronounced in those women who had the highest 10-year breast cancer risk bask on traditional life-style and reproductive profile risk factors.[58] Similar effects were found for women with low risk for developing breast cancer. However, for those with moderate risk for developing breast cancer based on the traditional risk factors, alcohol consumption had no further effect on developing cancer. While these results are complicated, similar ‘U-shaped’ or nonlinear relationships have been found for other factors and risk of breast cancer.[59]

 

Another study found no overall effect of alcohol consumption on breast density; however, among women with past hormone therapy, those who consumed more than 5 grams of alcohol/day had denser breasts.[60]

 

What are the effects of alcohol consumption on women who have been diagnosed with breast cancer?

There are several studies examining possible associations between alcohol consumption in women living with a diagnosis of breast cancer and later breast-cancer related events. Methodological differences between studies—especially how alcohol is measured and whether alcohol intake pre-and post-diagnosis is considered or just post-diagnosis consumption—make comparing and contrasting studies difficult. Never-the-less some relevant themes have emerged.

 

Although not all studies find this result, at least three papers report that alcohol consumption following a diagnosis of breast cancer is associated with an increased risk of breast cancer recurrence in postmenopausal women, but not premenopausal women.[61],[62],[63] At least two papers report that higher prediagnosis alcohol consumption increases risk of later recurrence following a diagnosis of breast cancer.[64],[65]

 

Similarly, not all studies found significant effects, but 2 of five in a major review found post-diagnosis alcohol consumption to be associated with development of a second cancer in the other breast.[66] For example, one study found that in addition to being obese and smoking after a breast cancer diagnosis, consumption of >7 drinks a week was associated with increased risk of contralateral breast cancer in women whose original cancer was ER+.[67]

 

Who is most likely to be exposed to alcohol?

Women and men who consume alcohol. A growing experimental literature using rodents indicates that in utero exposures to alcohol (from maternal consumption) also may increase later adult risk of developing mammary tumors.[68]

 

Who is most vulnerable to health effects?

All people who consume alcohol at any age are vulnerable.

 

What are the top tips to avoid exposure?

Limit consumption of alcohol. Any reduction of consumption will reduce risk of later life breast cancer.

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