Green Tea: Metabolic Enhancer, Life Extender, Cancer Eradicator?

Much ado has been made of green tea over the last two decades. It’s been credited with increasing fat loss, preventing cancer, and even extending lifespans. BUT is any of this true? According to the research, two of these three claims are.

How green tea assists in weight loss

Research shows that green tea assists in weight loss by elevating the metabolic rate. A study published in the December 1999 issue of The American Journal of Clinical Nutrition demonstrated this. The purpose of the study was to “[investigate] whether a green tea extract, by virtue of its high content of caffeine and catechin polyphenols, could increase [24-hour] energy expenditure (EE) and fat oxidation in humans”¹ The findings showed that “Relative to placebo, treatment with the green tea extract resulted in a significant increase in [24-hour energy expenditure] ...”¹ The study's authors concluded that “Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.”¹

A year later, a second study – 'Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine, and sympathetic activity'² – established that it wasn't just green tea's caffeine content at work.

“We report here that a green tea extract stimulates brown adipose [adipose=fat] tissue thermogenesis to an extent which is much greater than can be attributed to its caffeine content per se, and that its thermogenic properties could reside primarily in an interaction between its high content in catechin-polyphenols and caffeine with sympathetically released noradrenaline (NA).”²

Subsequent studies validated these findings as well.

It was later discovered that another component of green tea affects weight loss as well: its ability to trigger apoptosis – the process of programmed cell death (PCD) – in fat cells. This component of green tea can do the same to mutated cells (more on that later). The study 'Green tea polyphenol epigallocatechin gallate inhibits adipogenesis and induces apoptosis in 3T3-L1 adipocytes' states that

“EGCG increased apoptosis in mature adipocytes [cells that make up adipose tissue], as demonstrated by both laser scanning cytometry and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays. Furthermore, EGCG dose-dependently inhibited lipid accumulation in maturing preadipocytes.”⁶

How green tea fights cancer

In the 1990s, some in the medical research community were ready to accept that green tea may prevent cancer. One paper, published in the journal Nature, suggested why this might be so.

“We have inferred (using molecular modeling) and subsequently demonstrated that one of the major ingredients of green tea inhibits urokinase, an enzyme crucial for cancer growth. … Polyphenols, among other compounds, showed good inhibitory potential. One of them, EGCG (a component of green tea), binds to [urokinase], blocking [active sites of the urokinase] catalytic triad ... Such localization of EGCG would interfere with the ability of [urokinase] to recognize its substrates and inhibit enzyme activity.”³

Human research studies proved that green tea could indeed prevent or arrest cancer growth. A 1999 study, 'Green tea and cancer chemoprevention', found that the polyphenol EGCG could activate apoptosis in cancer cells.

“Moreover, a case-control study on breast cancer patients revealed that high daily consumption of green tea was associated with a lower recurrence rate among Stages I and II patients. All the results suggest that consumption of green tea is a practical and effective cancer preventive both before cancer onset and after cancer treatment.”⁴

Green tea does not extend the lifespan

There are studies that suggest green tea can reduce mortality in regards to specific ailments – The Ohsaki Study, for example, but this is not evidence of lifespan extension. According to The Ohsaki Study,

“Green tea consumption is associated with reduced mortality due to all causes and due to cardiovascular disease but not with reduced mortality due to cancer.”⁵

So, even though green tea was found to help protect against cancer, it did not reduce the mortality rate associated with the disease.

It may be argued that anything capable of preventing the onset of a potentially fatal illness is prolonging lifespan; however, aside from disease prevention, there's no conclusive evidence that drinking green tea can extend one's lifespan beyond what would be experienced otherwise.

History of green tea

The history of green tea is long and illustrious; originating from China, it has been associated with many cultures in Asia from Japan to the Middle East. There is archaeological evidence that it has been consumed for almost 5000 years, with China and India, respectively, being the first two countries to cultivate it. Green tea has been used as a traditional medicine in those countries as well as Japan and Thailand to help everything from controlling bleeding and helping to heal wounds to regulating body temperature, blood sugar and promoting digestion.

Ancient tomes such as 'The Kissa Yojoki (Book of Tea)', written by Zen priest Eisai in 1191, describes how drinking green tea can have a positive effect on the five vital organs, especially the heart. The book also discusses the tea’s other medicinal qualities, which include easing the effects of alcohol, acting as a stimulant, curing blotchiness, quenching thirst, eliminating indigestion, curing beriberi disease, preventing fatigue, and improving urinary and brain function. 'The Kissa Yojoki' was written more than 800 years ago, but the same claims and more profound ones are still being made today.