We've discussed the benefits of coffee on several occasions, although it's a controversial topic, with detractors claiming it has no health benefits. It's important to note that more scientific studies have proven the benefits and advantages of coffee consumption.
Therefore, in this installment we want to share with you the main findings of a study entitled "Coffee consumption decreases the risk of postmenopausal breast cancer: A dose-response meta-analysis of prospective cohort studies."
Before moving forward with this article, it is necessary to define two terms that we will encounter in the following: meta-analysis and prospective cohort studies.
In statistics, a meta-analysis refers to a set of methods aimed at comparing and combining the results of different studies, with the hope of identifying patterns among the study results, sources of disagreement between those results, or other interesting relationships that may come to light.
Prospective cohort studies are similar to randomized clinical trials in that the subjects are followed throughout their exposure until the occurrence of the event of interest. That is, they are used to determine the occurrence of a specific event in a group of individuals initially free of the event or disease under study.
To put this study into context, breast cancer is the most frequently diagnosed cancer and one of the leading causes of cancer-related death among women. Global and European estimates of women diagnosed with breast cancer in the past five years were more than 6.2 million and 1.8 million, respectively, in 2012. Significant improvements in early diagnosis and treatment have led to a reduction in mortality over the past two decades. However, potential risk factors need to be assessed and preventive measures improved to reduce the global burden of this disease.
In this regard, the objective of the study in question was to conduct a dose-response meta-analysis to summarize the evidence from prospective cohort studies regarding the association between coffee consumption and breast cancer risk.
The search strategies focused on conducting a systematic search of electronic databases up to March 2017 to identify relevant studies; risk estimates were retrieved from the studies; and a linear and nonlinear dose-response analysis modeled by restricted cubic splines was performed.
The following criteria were taken into account for the study:
- A prospective design.
- Coffee consumption as an exposure of interest.
- The incidence of breast cancer as a result.
- The measure of association (relative risk or risk ratio) with a 95% confidence interval provided for 3 or more quantitative categories of coffee consumption.
A manual search of the reference lists of retrieved manuscripts was also performed to identify additional studies not previously identified. In the case of duplicate published cohorts, the one with the highest number of cases/complete cohort or the longest follow-up for the endpoint of interest was included.
Regarding data extraction , data were extracted from all identified studies using a standardized extraction form. The following information was extracted from each article: first author's name; year of publication; name of the study cohort; country; sex of participants; age range of the study population at baseline; coffee consumption categories; coffee type; follow-up period; distribution of cases and person-years/number of participants across exposure categories; relative risks or hazard ratios, with 95% CIs for all exposure categories; and covariates used in adjustments. Data extraction was performed independently by two authors. Discrepancies were resolved by consensus discussion.
For the purposes of this meta- analysis , relative risks (RRs) or risk ratios (HRs) with 95% confidence intervals (CIs) were extracted for all coffee consumption categories based on the best-fitted models. Pooled effects were assessed using random-effects meta-analyses in which RRs and HRs were treated as equivalent risk measures, and the relative risk term refers to both.
Characteristics of the studies
The systematic search identified 1,724 studies, of which 1,533 were excluded after reviewing the title and 162 after reviewing the abstract. Of the 29 publications selected for full-text review, 8 were excluded because they did not meet the research criteria.
Results
A total of 21 prospective studies were selected for either dose-response analysis, highest versus lowest consumption category, or subgroup analysis.
Dose-response analysis of 13 prospective studies showed no significant association between coffee consumption and breast cancer risk in the nonlinear model. However, an inverse relationship was found when the analysis was restricted to postmenopausal women. Consuming four cups of coffee per day was associated with a 10% reduction in the risk of postmenopausal cancer (relative risk, RR 0.90; 95% confidence interval, CI 0.82 to 0.99). Subgroup analyses showed consistent results for all potential confounders examined.
In conclusion , the study found no significant association between coffee intake and breast cancer risk overall, but coffee consumption may be a protective factor for postmenopausal breast cancer risk. Further evidence considering specific population subsets and strata is needed to corroborate the associations found.
Based on all the above, it can be said that coffee consumption represents a health benefit, specifically helping us prevent postmenopausal breast cancer.