Drinking one alcoholic beverage daily can increase a woman's risk of developing breast cancer, while engaging in vigorous exercise can decrease breast cancer risk, according to a report released Tuesday.

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Report details

For the report, published by the American Institute for Cancer Research and the World Cancer Research Fund, researchers reviewed 119 studies on the effects of diet, nutrition, and physical activity on breast cancer. Overall, the researchers evaluated international data on more than 12 million women and more than 260,000 cases of breast cancer.

To evaluate the link between breast cancer and alcohol consumption, the researchers analyzed 10 large cohort studies involving 4,000 pre-menopausal women who were diagnosed with breast cancer, and 22 large cohort studies involving 35,000 post-menopausal women who were diagnosed with breast cancer.

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Findings

According to the report, daily consumption of about 10 grams of alcohol—the equivalent of one small glass of beer, wine, or other alcohol—is linked to a 5 percent increase in breast cancer risk among pre-menopausal women, and a 9 percent increase in breast cancer risk among post-menopausal women. According to "To Your Health," standard alcoholic drinks contain about 14 grams of alcohol.

In contrast, researchers found that engaging in vigorous physical activity was associated with reduced breast cancer risk. According to the report, participating in vigorous physical activity was linked with a 17 percent decrease in breast cancer risk among pre-menopausal women and a 10 percent decrease in breast cancer risk among post-menopausal women.

The researchers also found that breastfeeding is linked with a decreased risk of developing breast cancer. Further, the researchers found a link between obesity during ages 18 to 30 and lower breast cancer risk in pre-menopausal women. However, obesity beyond age 30 was linked with an increased risk of post-menopausal breast cancer, according to the report.

In addition, the researchers found limited evidence showing a link between a decrease in breast cancer risk and consumption of:

• Dairy products;
• Foods containing carotenoids, such as apricots, carrots, and kale; and
• Non-starchy vegetables.

Comments

Anne McTiernan, a lead author on the report and a researcher at the Fred Hutchinson Cancer Research Center, said the findings suggest "there is no level of alcohol use that is completely safe in terms of breast cancer." But, she added, "If a woman is drinking, it would be better if she kept it to a lower amount" in regard to breast cancer risk.

Chin-Yo Lin, a researcher at the University of Houston who was not involved with the report, said there are various reasons alcohol and breast cancer risk could be linked, including that "alcohol is converted into acetaldehyde, a chemical that can cause mutations in DNA, which can potentially lead to cancer" in exposed tissues. Lin said several "studies have shown that alcohol can enhance the actions of estrogen in breast cancer cells."

Kathryn Ruddy, an oncologist at the Mayo Clinic College of Medicine, said the evidence is "very clear that vigorous exercise protects against the development of breast cancer, and alcohol increases the risk of breast cancer, but the data are much more limited regarding the impact of any particular food on risk." Ruddy added that "there will be additional studies forthcoming to further clarify optimal strategies for [cancer] prevention."

Jennifer Ligibel, an associate professor at Harvard Medical School who was not involved with the report, said the findings' suggestion that obesity during young adulthood is linked with decrease breast cancer risk should not deter women from considering the other risks associated with obesity, such as Type 2 diabetes and an increased risk of cancer recurrence (McGinley, "To Your Health," Washington Post, 5/23; Howard, CNN, 5/23;Bowerman/Rossman, USA Today, 5/23; American Institute for Cancer Research and the World Cancer Research Fund report, May 2017).