Green tea is one of the most important cancer fighting foods. Many scientific studies show that it protects against cancers of the breast, prostate, lung, colon and bladder.
One of the most important reasons that green tea exhibits such good health promoting properties is that it is endowed with a large number of antioxidant compounds. Of these, epigallocatechin gallate (EGCG) is the most important and is unique to green tea.
However these compounds have beneficial effects in addition to those provided by their antioxidant properties. Other non-antioxidant compounds in green tea make a significant contribution to its cancer preventing properties through anti-inflammatory and other properties.
One of the few placebo controlled clinical studies to look at the effects of green tea on cancer was carried out on men who had early cancer of the prostate gland. After one year, only 3% of those taking green tea extract showed evidence of disease progression while 30% of those in the placebo-taking control group had developed signs of more advanced disease.
A couple of other very recent studies have thrown up some interesting results that show why green tea helps prevent cancer in some people and not in others.
EGCG and other catechin flavonoids, although abundant in green tea, are vulnerable to metabolic breakdown once they have entered the blood stream. The enzyme responsible for the metabolism of green tea is more active in some people than in others. The difference in enzyme activity is governed by an individual’s genetic make up.
Individuals whose genes code for high enzyme activity metabolize EGCG and other compounds in green tea more rapidly than those with genes that code for low enzyme activity. A consequence of the greater enzymatic activity of those in the first group is a reduced bioavailability of EGCG compared to those in the second group.
A survey of green tea drinkers found that women who are in the second, low-enzyme activity group derived considerable protection against breast cancer. While those women who fell into the high enzyme activity group failed to derive any protective benefits against breast cancer as their bodies destroyed the EGCG before it could do any good.
The increased activity of a well known peptide in the body, angiotensin II has been implicated in the production of free radicals that, in turn, aggravate the formation of breast cancer.
Angiotensin II is converted from its precursor by angiotensin converting enzyme (ACE). Women who have a genome that codes for high ACE activity produce more angiotensin II than those whose genotypes code for low ACE activity. The raised levels of angiotensin II that are associated with higher than normal levels of ACE, are responsible for the production of cancer-causing free radicals.
A recent survey found that those women who have the high activity ACE genotype derive substantial protection against breast cancer if they drink green tea regularly.
The reason is that EGCG and other antioxidant compounds in green tea neutralize the increased numbers of free radicals produced by those women who, because of their genetic make up, have higher than normal levels of ACE and therfore higher than normal levels of free radical-producing angiotensin II.
Drinking four to six cups of tea day is unlikely to cause any adverse effects and provides adequate quantities of EGCG and other polyphenols. However caffeine-free green tea is obtainable for those who avoid drinking beverages containing caffeine. The bioavailability of EGCG is much higher when green tea is taken on an empty stomach and should therefore be taken between meals to optimize its beneficial effects.
As with many other valuable plant species, green tea has shown that its principal value to human health is as a preventive rather than a curative agent.
The research into this important beverage has also demonstrated how phytochemicals in our diets can compensate for deficiencies in our genetic make up. Scientific research into other important plant foods indicates that many phytonutrients can even protect those individuals who have genes that make them susceptible to certain cancers.
Some of the evidence presented here shows that green tea does not necessarily help to prevent cancer in everyone who drinks it. It does not mean, however, that compounds in other plants will not do so. As our genomes differ from one person to another, so do our individual responses to disease, food and drugs. In order to maximize the health benefits that plant compounds can provide, we need to drink green tea and other beneficial beverages and eat a wide range of phytonutrient-rich plant foods.