Evidence regarding coffee consumption and breast cancer risk is inconsistent. Coffee has numerous compounds that have been reported to influence this risk, including caffeic acid, trigonelline, acrylamide, various polyphenols, hydroxyl hydroquinone, and other volatile aroma and heterocyclic molecules. Sorting out the relative contributions of these compounds to risk is challenging. In addition, women can vary greatly in their responses to coffee. These variations appear to be based primarily on hormonal and genetic factors. However, while the evidence is mixed, several studies have reported that caffeinated coffee consumption is associated with reduced risk of breast cancer after menopause. Now a new study has confirmed that coffee is associated with lower risk of postmenopausal breast cancer, especially hormone receptor negative (ER-/PR-) disease. Note, however, that the study did not investigate coffee's influence on the risk of breast cancer recurrence.

Coffee should be avoided or limited in some circumstances

Women with benign fibrocystic breast disease should avoid coffee. Caffeine consumption is associated with higher risk of benign breast disease and also appears to heighten breast cancer risk among women with the disease. One study found statistically significant positive correlations between caffeine consumption and both ER-/PR- breast cancer and breast tumors greater than 2 cm in size for women with benign breast disease.

Coffee should be avoided during chemotherapy. Coffee and other sources of caffeine may reduce the effectiveness of anthracycline chemotherapy drugs such as Adriamycin (doxorubicin). There is also some evidence that coffee could reduce the effectiveness of Taxol (paclitaxel) and other taxane chemotherapy as a result of its caffeic acid content.

High levels of caffeine consumption has been associated with higher risk of osteoporosis and therefore should be limited by many women taking aromatase inhibitors. This depends on whether bone mineral density is low or has been decreasing as a result of aromatase inhibitor treatment.

On the other hand, coffee has been reported to reduce the risk of breast cancer among BRCA2 mutation carriers. Moderate to high coffee consumption was also found to be associated with significantly lowered risk of recurrence in tamoxifen-treated breast cancer patients in one Swedish study.

Latest research links coffee to lower premenopausal cancer risk

The prospective study referenced at the beginning of this news story was designed to investigate the associations between coffee and black tea consumption and breast cancer risk. The study included 335,060 women in the European Prospective Investigation into Nutrition and Cancer (EPIC) Study cohort. The initially cancer-free women were enrolled and completed a dietary questionnaire between 1992 and 2000. Participants were followed until 2010, for an average of 11 years. During this time 1,064 of the women were diagnosed with breast cancer before menopause (premenopausal breast cancer), and 9,134 were diagnosed with breast cancer after menopause (postmenopausal).

Black tea consumption was not found to be associated with breast cancer risk, regardless of menopausal status. Women who did not drink decaffeinated coffee were observed to have a slightly lower risk of postmenopausal breast cancer than women who were low consumers. However, there was no evidence of a dose-response relationship. Women who drank decaffeinated coffee exclusively did not have significantly different risk of breast cancer than women who sometimes drank decaffeinated or those who did not drink any type of coffee. The authors conclude that decaffeinated coffee does not appear to be associated with breast cancer risk.

On the other hand, caffeinated coffee consumption was found to be associated with slightly lower risk of postmenopausal breast cancer. Women with high consumption had a 10% lower risk compared to those with low consumption. The results were similar when the women were divided according to hormone receptor status. However, the authors also observed a linear trend for lower risk of breast cancer with increasing coffee intake that was strongest for postmenopausal ER-/PR- disease. The risk of ER-/PR- disease was found to be lower by 4% for every 100 ml increase in coffee intake. Coffee consumption was not found to be associated with premenopausal breast cancer. The authors conclude that higher caffeinated coffee intake may be associated with lower risk of postmenopausal breast cancer.

Please see our article on coffee for more information.