This article is part of our October 2021 special issue. Download the full issue here.
Zheng KH, Zhu K, Wactawski-Wende J, et al. Caffeine intake from coffee and tea and invasive breast cancer incidence among postmenopausal women in the Women’s Health Initiative [published online ahead of print, 2021 Aug 21]. Int J Cancer. 2021;10.1002/ijc.33771. doi:10.1002/ijc.33771
To determine if there is an association between caffeine intake from coffee or tea and the formation of invasive breast cancer in postmenopausal women
Prospective, observational study
The Women’s Health Initiative (WHI) recruited close to 100,000 women from 1993 to 1998 to participate in their observational study. Of these, 79,871 racially and ethnically diverse women from 40 centers across the United States were included in the present study. They were postmenopausal at recruitment and ranged in age from 50 to 79 years. Investigators excluded women from the present analysis if they had a history of cancer or had cancer at the onset of the study.
Study Parameters Assessed
In an annual survey, the study participants were asked questions about their intake of caffeinated and decaffeinated coffee and tea, with participants noting either none, 1 cup, 2 to 3 cups, 4 to 5 cups, or 6 or more cups. Caffeine intake from other sources was not included and is not part of this study. The original study was conducted with the annual survey over a 10-year period; however, there were 2 additional 5-year extension studies encompassing up to September 2015. Data were also collected on age, race, ethnicity, education, smoking status and intensity, alcohol consumption and frequency, sleep duration, exercise, caloric intake, hormone therapy history, age at menarche, age at menopause, age at first full-term birth, parity, and family history of breast cancer. Further, a healthy eating questionnaire was used, and body mass index (BMI) was calculated from the height and weight collected by investigators.
Primary Outcome Measures
The incidence of invasive breast cancer, with data collected including hormone receptor status, HER2 (human epidermal growth factor receptor 2) receptor status, stage, grade, size, tumor type, nodal status, and histology.
Investigators put these outcomes through multivariable analysis using covariates in groups of demographic variables (age, race, ethnicity, and education), lifestyle variables (smoking, alcohol, caloric intake, exercise, healthy eating scores, BMI, and sleep duration), and reproductive variables (hormone therapy use, menarche, menopause, age at first birth, parity, and family history of breast cancer).
When investigators accounted for all of the variables, they observed no significant associations between risk of invasive breast cancer and consumption of various amounts of caffeine through coffee or tea consumption. The lack of association was maintained when data were isolated for receptor subtypes, grade, stage, and histology.
In subgroup analysis, participants who drank 2 to 3 cups per day of decaffeinated coffee had an increased risk of hormone receptor–positive cancer; however, this was no longer statistically significant after accounting for multiple comparisons.
There was a statistical significance in the heterogeneity of tea intake between hormone receptor status (ER positive vs negative) and histological subtype (ductal vs lobular).
The positive or negative connections between coffee and tea consumption and cancer risk in general have long been debated. What we have found through numerous studies is that there are many variables to consider. Coffee and tea contain many phytochemicals in addition to caffeine; thus the studies to date should not be interpreted as a surrogate for caffeine intake. In addition, there are changes that occur in the processing of the coffee berries and tea leaves—roasting or fermenting, as well as the natural variations in phytochemicals that would be found in different growing regions—and this adds to the complexity of precisely what is being studied.
The study currently under review sought to determine if caffeine intake from coffee or tea was associated with breast cancer incidence in postmenopausal women. The results imply that there is no difference in breast cancer incidence regardless of intake of regular or decaffeinated coffee or tea. That said, one of the study’s limitations was the lack of inclusion of other sources of caffeine, such as energy drinks, soft drinks, or chocolate. The lack of inclusion of these negates the validity of this being a study on caffeine effects and points more to it being a study of the associations of coffee or tea consumption and breast cancer incidence.
The positive or negative connections between coffee and tea consumption and cancer risk in general have long been debated.
These findings are similar to those of the Black Women’s Health Study,1 the Swedish Women’s Lifestyle and Health Study,2 and other cohort studies. However, it contrasts with the beneficial effects of regular coffee intake on incidence of breast cancer found in the Nurses’ Health Study. In the August 2021 edition of NMJ, there is an excellent overview by Jacob Schor, ND, FABNO, of the analysis of the latter study.
This study was more specific to the risk of primary diagnosis of invasive breast cancer with coffee or tea consumption, as opposed to the effects of said consumption after breast cancer diagnosis. A recent analysis of Nurses’ Health Study data by Farvid, et al found there was a statistically significant reduction in death from breast cancer with the consumption of more than 3 cups per day of coffee.3
What do these studies mean for clinical practice? According to this study, there seems to be no reason to alter coffee or tea consumption in primary prevention of invasive breast cancer. However, after the diagnosis of invasive breast cancer, coffee consumption of more than 3 cups per day may be added to the treatment protocol as a tasty tool to reduce the breast cancer specific mortality in our patients, at least in those patients who are able and willing to do so.
The possible caveat to altering coffee or tea consumption in primary prevention remains the recommendation of green tea high in catechins. In a meta-analysis published in 2020, Wang et al found that there is reduced incidence of breast cancer with long-term, high intake of green tea.4 This may be different from the findings of the Women’s Health Initiative Study due to the specific type of tea intake they analyzed.