Green tea has long been shown to possess anticancer properties but continues to be an enigma for mainstream Western oncologists who question the conflicting data seen in human studies. While green tea is clearly safe to drink, and clearly shows anticancer properties in the lab, some large studies in humans have not shown strong benefits. But others have.
New research at Penn State University in the US is adding to the body of in vitro laboratory evidence showing remarkable and clear benefits of green tea. The work there of Joshua Lambert, Ph.D., and others, is looking at green tea in the context of oral cancer. Lambert’s in vitro testing has shown that green tea induces oxidative stress in oral cancer cells but also exerts antioxidant effects in normal cells. In other words, green tea selectively kills cancer cells.
In Asian countries, green tea is a staple drink, developed over 4,000 years ago in China from the plant Camellia sinensis. Of the many potentially beneficial constituent chemicals in green tea, the catechin EGCG (epigallocatechin-3-gallate) is believed to have the most potent effect. Catechins are a type of flavonoid, which in turn comprise the most common group of polyphenols in the human diet. People in Asia frequently consume 3 to 5 cups per day, yielding at least 250 mg/day of catechins.
Exactly how catechins protect healthy cells while killing cancer cells is not yet clearly understood, but there are several hints. Lambert’s team found evidence that EGCG selectively affects the activity of a protein called sirtuin 3, or SIRT3, which “plays an important role in mitochondrial function and in anti-oxidant response in lots of tissues in the body.” EGCG appears to turn off SIRT3 in cancer cells, and turn it on in healthy cells. Other studies have shown that the p57 tumor suppressor gene is responsible for the survival of healthy cells when exposed to green tea polyphenols.
In vitro and epidemiological studies of green tea in Asian countries largely show chemopreventive and therapeutic properties in most types of cancer, especially GI cancers (esophageal, stomach, bladder, and other gastrointestinal cancers). There is substantial evidence that green tea also reduces risk of stroke, lowers blood pressure, lowers fasting blood sugar, lowers total and LDL cholesterol, and reduces risk of Alzheimer’s disease.
A plausible explanation for why large human studies have not found consistent chemopreventive effects from green tea is the fact that different hybrid source plants, growing conditions, horticultural practices, production processes, and even preparations, all contribute to the constituent chemicals found in green tea. A 2012 study by the independent research group ConsumerLab.com found widely varying amounts of EGCG in green tea products. In general, they found that bottled green teas ad the least amount of EGCG, while standardized EGCG extract supplements provided a reliable way of getting the targeted amount. EGCG supplements also provided the least expensive way to consume EGCG. Hopefully future human studies will utilize standardized extracts.
Green tea interferes with some and perhaps all proteasome inhibitors, most notably the chemo drug bortezomib (Velcade).