No associations were found between coffee consumption and overall cancer rates (for all cancer sites combined), or for prostate or colorectal cancer. However, boiled coffee was associated with increased risk of respiratory tract cancer in men, but not women, and significantly increased risk of pancreatic cancer. Total coffee consumption (boiled plus filtered) was also found to be associated with significantly reduced risk of renal cell cancer.
Women who drank boiled coffee at least four times per day were found to have half the risk of breast cancer compared to women who consumed it less than once per day. However, when examined by menopausal status, total coffee consumption (boiled plus filtered) was found to be associated with a 69% increased risk of premenopausal breast cancer and 40% reduced risk in postmenopausal breast cancer. Filtered coffee consumption was associated with a slightly higher (76%) increase in risk of premenopausal breast cancer and somewhat greater (48%) reduction in risk of postmenopausal breast cancer, but the differences between total and filtered coffee consumption were not statistically significant. The authors conclude that brewing method may be relevant in investigations of coffee consumption and risk of various types of cancer, but this must be confirmed in future studies.
Comments concerning coffee and risk of breast cancer
As the studies below show, evidence regarding coffee consumption and breast cancer risk is inconsistent. Coffee has numerous components such as caffeic acid, trigonelline (a phytoestrogen), various polyphenols, and volatile aroma and heterocyclic compounds that have been reported to influence cancer risk. The study described above was designed, in part, to demonstrate that since boiled coffee may contain more of these compounds, it may have different effects on cancer risk than filtered coffee. However, in the case of breast cancer, differences between the coffee-specific fatty acid contents of boiled versus filtered coffee appear not to be important. Variations among women in the associations between coffee consumption and risk of breast cancer appear to be based primarily on hormonal and genetic factors.
What is know then, about coffee consumption and breast cancer risk? Below we summarize our conclusions, based on the available evidence:
- Caffeine consumption has been associated with higher risk of fibrocystic breast disease, which in turn is a marker of increased breast cancer risk. One study found that, for women with benign breast disease, statistically significant positive correlations existed between caffeine consumption and both estrogen receptor negative, progesterone receptor negative (ER-/PR-) breast cancer and breast tumors greater than 2 cm in size. Women with benign breast disease should avoid coffee.
- Caffeine consumption has also been associated with higher risk of osteoporosis and therefore should be limited by women taking aromatase inhibitors.
- Low to moderate coffee consumption appears to be safe for postmenopausal women who are estrogen receptor positive (ER+) breast cancer survivors.
- Drinking coffee (with caffeine) may reduce breast cancer risk for BRCA1 and BRCA2 mutation carriers.
- For other women (i.e., no breast cancer diagnosis, not a BRCA1/BRCA2 carrier, or ER- breast cancer survivor), the potential risks of heavy coffee consumption appear to outweigh the potential benefits and it would appear prudent to limit coffee consumption.