Scientists have been looking at whether or not the ingestion of tea can prevent or even treat cancer for more than three decades now. Every so often, eye-popping headlines emerge linking the beverage to a reduced risk of a specific cancer.
A deeper dive, though, yields conflicting information. Although tea, especially green tea, shows great promise in both test tube and animal studies, tests on humans have been less conclusive.
Tea - A Quick Primer
While many products commercially available today bear the label “tea,” researchers studying the role of tea in cancer prevention and treatment are referring specifically to a plant known as Camellia sinensis. You don’t look for Camellia sinensis on your supermarket shelves, though. You select from varieties such as oolong, white, black, green or yellow. These varieties are created through different processing methods. The more processing and oxidation the tea leaves undergo, the darker the leaf and the darker the resulting tea.
Because it undergoes less oxidation and processing, green tea has higher levels of plant chemicals known as “polyphenols” than darker teas do. Specifically, green tea contains more of a certain type of polyphenol — catechins.
Catechins can be found in cocoa, berries and other foods but are especially plentiful in green tea. Of the catechins in tea, epigallocatechin-3-gallate (EGCG) is both the most abundant and the most studied.
Research into whether and how tea impacts human health has taken many forms, but the bulk of the research has been into green tea and EGCG more specifically. Much of this research has centered on cardiovascular disease and cancer. Research into the health effects of green tea has been conducted on humans, animals and in laboratory experiments.
What Have Studies Shown?
While laboratory and animal studies have shown green tea or its components may have anti-cancer properties,results from research into humans is mixed. This report, from Mount Sinai Medical Center, provides an excellent summary of the current state of research.
According to the Mount Sinai report, there is evidence that green tea consumption correlates favorably in preventing the following types of cancer: bladder, pancreatic, prostate and skin. It was not shown to have an effect in preventing breast cancer.
Additionally, green tea or its components correlated favorably to better long term outcomes in both breast and ovarian cancer.
However, results were mixed or inconclusive for a number of other cancers. For example, a preventive effect was seen for lung cancer in women, but not men. Results were also conflicting for esophageal and stomach cancers.
National Cancer Institute (NCI) lays out a variety of safety considerations for anyone considering using green tea as part of their cancer prevention or treatment protocol. While tea is generally recognized as safe and is a widely consumed food product, certain individuals should not consume green tea, including people taking many frequently prescribed medications. Mount Sinai offers a list here. Moreover, green tea contains caffeine which can impact some people adversely, especially when consumed in large amounts.
Anyone undergoing chemotherapy should speak to their physician before consuming green tea. Green tea consumption should be avoided by anyone taking the chemotherapy drug bortezomib as it has been shown to reduce that drug’s effectiveness.
Additionally, green tea is contraindicated for anyone on a blood-thinning medication such as Warfarin because it contains Vitamin K. Green tea may also impact medications such as blood pressure drugs, birth control pills, antibiotics and many more. Consult your doctor and/or pharmacist about potential interactions. Please visit the Mount Sinai site for other health conditions that might make green tea consumption risky.