Reference
Li J, Seibold P, Chang-Claude J, Flesch-Janys D, Liu J, Czene K, Humphreys K, and P. Hall. Coffee consumption modifies risk of estrogen-receptor negative breast cancer. Breast Cancer Res. 2011;13:R49.
Design
Population-based case-control study. Data was obtained from the participants through a mailed questionnaire with the nutritional data collected through a food-frequency questionnaire. Validation of the questionnaire was done via a face-to-face interview using a standardized questionnaire. Data on the consumption of coffee 1 year before interview, specified in cups per week (based on portion size and frequency), where a cup is equivalent to 5 oz (1.5 dL), was collected. The hormone receptor status of the breast cancers was obtained from the medical records of the participants. All data was analyzed using unconditional logistic regression and linear regression models. Multivariate-adjusted Odds Ratio (OR) estimates and corresponding 95% confidence interval (CI) were estimated for each category of coffee consumption. The results of this study were validated with results extracted from a previously published German MARIE population study.
Participants
Parent study consisted of women between the ages of 50–74, born and living in Sweden. The final study group consisted of 2,651 women with diagnosed invasive breast cancer who were identified through cancer registries. The final control group of 5,395 women was frequency-matched to the cases by age, and all controls were without a previous diagnosis of cancer.
Study Parameters Assessed
This study examined the relationship between coffee consumption and breast cancer risk, stratified by hormone receptor sub-type. The relationship between coffee consumption and other breast cancer risk factors was also assessed.
Key Findings
This study demonstrated a 20% reduction in overall breast cancer risk in women (model adjusted for age only) at a consumption level of more than 5 cups per day compared to one cup or less coffee intake daily (OR>5 cups/day: ≤1 cup/day: 0.80 (CI: 0.64–0.99), P=0.028). Interestingly, when the model was further adjusted for hormone replacement therapy (HRT), smoking, education, and average daily alcohol consumption, the protective effect on overall breast cancer risk was no longer found to be statistically significant. This suggests that these other risk factors overshadowed the influence of coffee. Further analysis demonstrated that coffee consumption reduced the risk of estrogen receptor negative (ER-) breast cancers by 57% (OR>5 cups/day: ≤1 cup/day for multivariate model: 0.43 (0.25, 0.72), P=0.0003), but had no impact on estrogen receptor positive (ER+) tumor risk. The risk reduction in ER- tumors was independent of progesterone receptor status.
Practice Implications
In Sweden, a nation of coffee lovers, the median intake of coffee is 15 oz daily, making this study particularly welcome news there. Being half Swedish myself, a breast cancer survivor, and a lover of coffee, I was particularly delighted to see this study. Unfortunately, even for a Swedish coffee aficionada like me, it is a stretch to consume more than 25 oz of coffee daily, the amount linked with the reduction of risk. The risk reduction was not evident at lower consumption levels. Additionally, other short- and long-term consequences of consuming this quantity of coffee daily were not assessed in this study. Substantial intake of coffee could impact cortisol levels, digestive function, and neurological activity.
Another challenge to the practical implications of this study is the preparation of coffee studied. The majority of coffee consumed in Sweden is boiled. The majority of coffee consumed in U.S. is filtered. Other studies have failed to find a preventive effect with filtered coffee, likely due to the fact that the filtering removes compounds that may confer this preventive benefit.
Despite these issues, coffee is one of the most popular beverages in the world, and therefore its impacts on health and disease risk should remain an important research focus. An number of studies link the intake of coffee with lowered risk of cancer, including cancers of the prostate, brain, liver, and now breast. Coffee is a complex mixture of caffeine and polyphenols. In fact, coffee is considered to be a major dietary source of antioxidants for individuals, especially those who lack vegetables and fruits in their diet. However, coffee, like any other food, contains a multitude of phytochemicals with varying effects. There are some compounds (eg, trigonelline) in coffee that activate the estrogen receptor, which may explain the lack of benefit in preventing ER+ cancer in this study. Conversely, high consumption of coffee increases endogenous production of enterolactone, another phytoestrogen that reduces ER- breast cancer risk.
The most conservative approach at this point is to refrain from recommending coffee for breast cancer prevention.
Where does this leave us? This study clearly demonstrates a preventive effect of ER- breast cancer from consumption of at least 5 cups of boiled coffee daily (in Swedes). The body of literature on the relationship between coffee intake and breast cancer is quite mixed. There are studies with similar findings to those of this study.1 However, there are also studies that show a reduction in risk of ER+ breast cancers from coffee.2 Yet other studies suggest an increased risk of ER- breast cancer associated with caffeine intake.3 This situation is eerily similar to the confusion regarding the impact of soy intake on breast cancer risk. Until more definitive recent studies, it was unclear whether soy was protective or not. Recent studies have finally added clarity to this area and have confirmed a risk reduction effect from soy on both ER+ and ER- breast cancer.4 Whether definitive studies on coffee will result in the same conclusions is unknown. Therefore, the most conservative approach at this point is to refrain from recommending coffee for breast cancer prevention. Utilizing more reliable strategies with a firmer base of evidence is advisable. However, should someone already be consuming coffee and unwilling to stop, the emerging body of data is suggestive of an insignificant to possibly protective effect.
Limitations
The authors of this study note that a limitation was that receptor status was available for only 65.4% of the Swedish population, challenging the validity of some of the observed trends. Additionally, the data collected in this study, along with many other diet-focused population cohort studies, is self-reported data and therefore is subject to recall bias. This limitation might be somewhat blunted here due to the repetitive nature of coffee drinking and therefore increased accuracy of recall.
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