A 2020 meta-analysis on green tea and breast cancer including 16 studies reported a pooled relative risks of 0.86 (95% CI: 0.75–0.99). Table 1 provides an overview of meta-analyses on green tea consumption and site-specific cancer risk. įigure 2 provides overall risk from most comprehensive and recent meta-analyses for each cancer site. A decreased risk of total cancer mortality was reported among Japanese women HR = 0.91 (0.85–0.98), but not men HR = 1.02 (0.89–1.10). The association between green tea consumption and total cancer risk is inconclusive. In this review, we aim to deliver an objective overview of the current evidence from meta-analyses, individual studies and reports on green tea and health outcomes with a focus on individual cancer sites, cardiovascular disease, and diabetes. Previous green tea reviews emphasized general health benefits in vitro or specific outcomes. Compared to coffee and black tea fewer meta-analyses are available on individual health outcomes and therefore a strict umbrella review, exclusively including meta-analyses, was not deemed the most appropriate design to capture the breadth of evidence for this study. Įvidence on the health effects of green tea and various health outcomes is accruing, 2020 is an opportune time to review the evidence. Numerous meta-analyses and individual studies exist on the association between green tea and various health outcomes particularly individual cancers. The International Agency for Research on Cancer Monographs Volume 51 published in 1991 also includes an evaluation of green tea carcinogenic risks to humans.
Teacode review update#
The World Cancer Research Fund Third Expert Report and Continuous Update Project (CUP) includes a discussion on green tea consumption and site-specific cancers, however, evidence was too limited to draw a conclusion. Various potential health benefits of green tea have been reviewed including anti-inflammatory, antibacterial, neuroprotective, and cholesterol-lowering effects, which may have an impact on cancer and cardiometabolic risk. A 2014 review includes a useful overview of catechin’s composition of brewed green tea based on the USDA Database for the Flavonoid Content. Green tea is made from leaves that are steamed (Japan) or roasted (China) shortly after harvesting to inactivate enzymes, preventing oxidative fermentation, then pressed and finally dried. Green tea’s popularity is increasing globally. Green tea is commonly consumed in East Asian countries such as China and Japan, as well as some parts of North Africa and the Middle East. This review concludes that green tea consumption overall may be considered beneficial for human health. Fewer studies investigated the association between green tea and other health outcomes such as cognitive outcomes, dental health, injuries and respiratory disease. The evidence for diabetes-related health outcomes is less convincing, while the included meta-analyses generally suggested an inverse association between green tea and BMI-related and blood pressure outcomes. The literature overall supports an inverse association between green tea and cardiovascular disease-related health outcomes. No studies reported adverse effects from green tea related to cancer although consuming hot tea has been found to possibly increase the risk of esophageal cancer and concerns of hepatotoxity were raised as a result of high doses of green tea. Mixed findings were observed for breast, esophageal, gastric, liver and a mostly null association for colorectal, pancreatic, and prostate cancer. For certain individual cancer sites: endometrial, lung, oral and ovarian cancer, and non-Hodgkins lymphoma the majority of meta-analyses observed an inverse association with green tea. This review captured evidence from meta-analyses as well as expert reports and recent individual studies. The aim of this review was to objectively evaluate the existing evidence related to green tea consumption and various health outcomes, especially cancer, cardiovascular disease and diabetes. Green tea is commonly consumed in China, Japan, and Korea and certain parts of North Africa and is gaining popularity in other parts of the world.
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