Coffee and tea consumption and the risk of invasive breast cancer in postmenopausal women

This article is part of our October 2021 special issue. Download the full issue here.

Relation

Zheng KH, Zhu K, Wactawski-Wende J, et al. Caffeine intake from coffee and tea and incidence of invasive breast cancer in 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

Study objective

To determine whether there is an association between caffeine intake from coffee or tea and the development of invasive breast cancer in postmenopausal women

Draft

Prospective observational study

Participant

The Women's Health Initiative (WHI) recruited nearly 100,000 women to participate in its observational study from 1993 to 1998. Of these, 79,871 racially and ethnically diverse women from 40 centers in the United States were included in the present study. They were postmenopausal and aged between 50 and 79 years at recruitment. Researchers excluded women from the present analysis if they had a history of cancer or had cancer at the start of the study.

Study parameters assessed

In an annual survey, study participants were asked questions about their consumption of caffeinated and decaffeinated coffee and tea, with participants reporting 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 through 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. A healthy eating questionnaire was also used and body mass index (BMI) was calculated from height and weight collected by the researchers.

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, lymph node status and histology.

The researchers subject these results to multivariable analysis using covariates in groups of demographic variables (age, race, ethnicity, and education), lifestyle variables (smoking, alcohol, calorie 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).

Key insights

When the researchers took all variables into account, they found no significant associations between the risk of invasive breast cancer and consumption of different 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 of decaffeinated coffee per day had an increased risk of hormone receptor-positive cancer; however, this was no longer statistically significant after multiple comparisons were taken into account.

There was statistical significance in the heterogeneity of tea consumption between hormone receptor status (ER positive vs negative) and histological subtype (ductal vs lobular).

Practice implications

The positive or negative associations 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. In addition to caffeine, coffee and tea contain many phytochemicals; therefore, previous studies should not be interpreted as a replacement for caffeine intake. Additionally, there are changes that occur in the processing of the coffee berries and tea leaves - roasting or fermenting, as well as the natural variations of phytochemicals found in different growing regions - and this adds to the complexity of what exactly is being studied.

The study currently under review sought to determine whether caffeine intake from coffee or tea is associated with the occurrence of breast cancer in postmenopausal women. The results imply that there is no difference in breast cancer incidence regardless of consumption of regular or decaffeinated coffee or tea. However, one of the limitations of the study was the lack of inclusion of other sources of caffeine such as energy drinks, soft drinks or chocolate. The absence of these factors negates the power of this study on caffeine effects and rather suggests that this is a study of the associations between coffee or tea consumption and breast cancer incidence.

The positive or negative associations between coffee and tea consumption and cancer risk in general have long been debated.

These results are similar to those of the Black Women's Health Study,¹the Swedish Lifestyle and Health Study for Women,²and other cohort studies. However, this is in contrast to the positive effects of regular coffee consumption on breast cancer incidence found in the Nurses' Health Study. The August 2021 issue of NMJ has an excellent overview of the analysis of the latter study by Jacob Schor, ND, FABNO.

This study was more specific to the risk of a primary diagnosis of invasive breast cancer with coffee or tea consumption, as opposed to the impact of this consumption after breast cancer diagnosis. A recent study by Farvid et al. Analysis of Nurses' Health Study data found that there was a statistically significant reduction in breast cancer deaths when consuming more than 3 cups of coffee per day.³

What do these studies mean for clinical practice? According to this study, there appears to be no reason to change coffee or tea consumption in the primary prevention of invasive breast cancer. However, after diagnosis of invasive breast cancer, coffee consumption of more than 3 cups per day can be added to the treatment protocol as a palatable agent to reduce breast cancer-specific mortality in our patients, at least in those patients who are able and willing to do so.

The possible caveat to changing 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 the incidence of breast cancer is reduced with long-term, high consumption of green tea.⁴This may differ from the results of the Women's Health Initiative Study due to the specific type of tea consumption analyzed.