May 15, 2018
Coffee decreases risk of postmenopausal breast cancer.
Jacob Schor, ND, FABNO
Denver Naturopathic Clinic News: denvernaturopathic.com
Denver Naturopathic Oncology: denvernaturopathiconcology.com
Another in a line of relevant studies on coffee and cancer risk was published in January of this year. Alessandra Lafranconi and colleagues produced a complex analysis of data gleaned from prior studies on the link between coffee consumption and risk of breast cancer. Not just risk in women but in various subgroupings of women. They collated data from twenty-one previously published prospective trials and compared amount of coffee consumed per day against relative risk of breast cancer from for categories including BMI, hormone receptor status and menopausal status.
Their analysis showed no significant association between coffee consumption and general breast cancer risk. However, an inverse relationship was seen when the analysis was restricted to post-menopausal women. That is, in English, the coffee postmenopausal women drank, the lower their risk for cancer. Consumption of four cups of coffee per day was associated with a 10% reduction in postmenopausal cancer risk (relative risk, RR 0.90; 95% confidence interval, CI 0.82 to 0.99).
Reference: Lafranconi A, Micek A, De Paoli P4 et al. Coffee Intake Decreases Risk of Postmenopausal Breast Cancer: A Dose-Response Meta-Analysis on Prospective Cohort Studies. Nutrients. 2018 Jan 23;10(2). pii: E112.
Now that’s rather interesting. These results tell us several things. First, it’s ok for women to drink coffee without worrying it will give them breast cancer, at least for the moment and especially if the women are post-menopausal. Granted this doesn’t tell us about women who have had breast cancer who are fearful of recurrence, but it makes me think they are probably ok as well. This information matters to many women who have abstained from coffee based on past recommendations from healthcare providers or through simple false assumption that coffee is ‘bad’. For many years coffee was presumed to be harmful to health despite little evidence to support that belief.
The relationship between coffee and breast cancer has been difficult to pin down. In recent years coffee has been viewed as often having potential benefit in human health. An August 2017 literature review suggested “…. coffee was associated with a probable decreased risk of breast, colorectal, colon, endometrial, and prostate cancers; cardiovascular disease and mortality; Parkinson’s disease; and type-2 diabetes.” 
Observational prospective cohort studies, suggest that moderate-to-high coffee intake is associated with lower risk of all-cause, cardiovascular and cancer mortality compared to lower consumption. 
It has been hypothesized that coffee consumption will affect risk of female cancers including breast, endometrial and ovarian, particularly in post-menopausal women. Recent analysis of the Nurses’ Health Study II grouped low coffee consumption in a dietary pattern that also included low intake of green leafy vegetables and cruciferous vegetables.  Prior attempts at meta-analysis of data looking at coffee and female cancer risk have failed to produce clear results in particular not finding definitive dose-response associations.  In Li’s 2013 meta-analysis that examined 16 cohort and 10 case control studies there was only a borderline association comparing highest versus lowest coffee consumption; there was however a significant inverse association between coffee consumption and estrogen receptor negative women and also BRCA1 positive women.  This suggested attention should be focused on the effect of coffee on more specific groups of women. Thus this study puts more focus on coffee impact on various subgroups.
[Review of Li’s study https://www.naturalmedicinejournal.com/journal/2011-07/coffees-effects-breast-cancer ]
This current analysis did just that, including results from 13 prospective studies with over 1 million participants. While it did not find a significant association between coffee consumption and overall breast cancer risk, in itself an important finding, it showed a significant inverse relationship, that is a decrease in breast cancer risk, in post-menopausal women. Consumption of four cups of coffee per day was associated with a 10% reduction in postmenopausal cancer risk (relative risk, RR 0.90; 95% confidence interval, CI 0.82 to 0.99).
In this study it did not matter if the woman was drinking caffeinated or decaffeinated coffee. Thus credit for the breast cancer protection cannot be given to caffeine; other compounds in coffee must be responsible. It could be the many antioxidants in coffee. It could be the effect coffee has on liver function or on metabolic syndrome. The exact role coffee plays and the mechanisms by which it might change breast cancer risk in this subgroup is unclear. No evidence has been reported that suggests coffee acts as an aromatase inhibitor, which is too bad as the idea of naming some coffee based medicinal using the word ‘aromatase’ has certain humorous appeal. We await future studies that may elucidate all of this.
In the meantime, it looks more and more clear that coffee does not increase breast cancer risk and may offer protection against certain subsets of breast cancer categories. These data are related to diagnosis of primary cancer and probably tell us little about changing risk of recurrence.
There is another fundamental problem with this data; the participants were not randomized as to who would drink coffee and who wouldn’t. These ‘free living people’ decided on their own whether or not to drink coffee and how much. It may well be that these self-selected groups divide themselves over a yet undefined quality that confounds these results. The obvious possibility is what we are seeing is a difference in liver function or digestive function. A percentage of people purposefully avoid coffee because it keeps them awake at night, likely a symptom of slow liver detoxification capacity. Might slower liver detoxification be independently associated with greater cancer risk and coffee avoidance is just a behavioral tell? Forcing patients to drink coffee might not change this fact of life for them and thus not change their innate risk of breast cancer. At the same time it probably won’t hurt.
1. Grosso, G, Godos J, Galvano F, Giovannucci EL, Coffee, caffeine and health outcomes: An umbrella review. Annu. Rev. Nutr. 2017, 37, 131–156.
2. Grosso G, Micek A, Godos J. et al. Coffee consumption and risk of all-cause, cardiovascular and cancer mortality in smokers and non-smokers:
A dose-response meta-analysis. Eur. J. Epidemiol. 2016, 31, 1191–1205.
3. Harris HR, Willett WC3, Vaidya RL, Michels KB. An Adolescent and Early Adulthood Dietary Pattern Associated with Inflammation and the Incidence of Breast Cancer. Cancer Res. 2017 Mar 1;77(5):1179-1187.
4. Malerba S, Turati F, Galeone C, et al. A meta-analysis of prospective studies of coffee consumption and mortality for all causes, cancers and cardiovascular diseases. Eur J Epidemiol. 2013 Jul;28(7):527-39.
5. Li XJ, Ren ZJ, Qin JW, et al. Coffee consumption and risk of breast cancer: an up-to-date meta-analysis. PLoS One. 2013;8(1):e52681.