5 min read · Dec 18, 2023
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Although the popularity of green tea in the Western world is a fairly recent phenomenon, its highly beneficial nutritional value has enjoyed a favorable reputation throughout many parts of Asia for thousands of years. Only recently has scientific research begun to understand green tea’s health benefits in relation to its high concentration of phytochemicals known as polyphenols, which include subclasses of tannins and gallic acid.
In this article, I will address commonly asked questions about polyphenols, catechins, epigallocatechin-3-gallate (EGCG), tannin, gallic acid, and caffeine.
Because this article ended up being quite long, I have broken the article into multiple parts. Here is a list of questions and topics I cover in this entire series so that you can skip to the question you want to read.
Polyphenols are antioxidants or substances that combat free radicals, which can damage DNA and alter or even kill cells in the body.
Also known as phenolics, they are chemical compounds that occur in plants. They have over one phenol unit, or building block, in every molecule. They give plants their color and help protect them from insects. Foods or drinks containing polyphenols will have an astringent bite to their flavor.
There are 8,000 types of polyphenols that have been found in edible plants, and half of them belong to a group called the flavonoids that is further subdivided into six categories.
Catechins, also called flavanols, and tannins are actually types of polyphenols. The leaves of the tea plant produce more catechins than any other plant. The fermentation and oxidation processes are believed to strip black and oolong teas of some antioxidants, so green tea has more catechins than the other types. EGCG is the most abundant catechin in tea.
One difference between a catechin and a tannin is size. Tannins are larger. A catechin with over 20 or more hydroxyl groups (-OH) is classified as a tannin.
Coffee and tea are the main sources of tannins in the human diet. Tannins help give coffee and tea their flavor.
Determining the amount of polyphenols in green tea is not a straightforward process, as some brands have more than others. A 2003 study of different green and black teas, for example, found that the amount of EGCG in green tea could range from 22 mg per 100 ml to nearly 100 mg per 100 ml. Similarly, the amount of catechins ranged from 52 mg per 100 ml to 216 mg per 100 ml.
EGCG, however, is the most abundant catechin in all of the teas. Epicatechin gallate (ECG) is the second most abundant, with numbers ranging from 22 mg per 100 ml to nearly 80 mg per 100 ml.
Green tea has far more catechins than black tea. The 2003 study showed that the amount of catechins in black tea ranged from none at all to 81.6 per ml, with the lowest numbers being in iced teas. While decaffeinated black teas had some catechins, they had no EGCG or ECG. The amount of EGCG in other black teas ranged from nearly 4 mg per 100 ml to around 74.5 mg per 100 ml, with a Darjeeling tea having by far the most. The amount of ECG ranged from approximately 1.4 mg per 100 ml to around 21.3 mg per 100 ml.
Conversely, black tea contains a family of polyphenols called theaflavins that do not occur in green tea.
Many people can use polyphenols, and they can be taken in supplement form. They also come in a variety of foods and drinks, many of which are quite tasty and enjoyable. (Who doesn’t like dark chocolate or green tea?)
Polyphenols are antioxidants and can therefore fight and even prevent disease. Some of the catechins found in tea may prevent the development of diabetes. Researchers suspect the catechins impede the gut’s absorption of glucose.
Polyphenols may help fight some types of cancer by reducing the size and/or number of tumors. Researchers are studying some polyphenols, like quercetin and resveratrol, to learn about their anti-aging and cancer-fighting properties.
The polyphenols found in green tea have been linked to a reduced risk of Parkinson’s disease. Other polyphenols found in vegetables and fruits may slow down the development of Alzheimer’s disease.
Polyphenols help prevent low-density lipoprotein (LDL) cholesterol from reacting with free radicals, thus slowing the development of atherosclerosis. Scientists have found that a diet based on plant foods reduces the likelihood of developing cardiovascular disease.
Researchers believe that polyphenols might prevent osteoporosis and some lung diseases, such as asthma. More studies need to be done, however.
There are no known side effects caused by the polyphenols themselves. Some of their plant sources may cause allergic reactions, however.
Green tea, however, can cause drug interactions. People taking anti-depressants, birth control pills, blood thinners, some heart medications, and some antibiotics should talk to their doctor before drinking green tea or taking supplements made from green tea.
Polyphenols can be eaten or drunk. In 2010, a group of French scientists ranked foods by their polyphenols and listed them by concentration or serving. The former can be misleading; some foods, like many herbs, have high concentrations of polyphenols but are eaten in such small amounts that they don’t contribute much to a meal. Cloves, for example, have the highest concentration of polyphenols of all, with over 15,000 mg per 100 grams, but they are eaten in such small amounts that they don’t even make the “Most Polyphenols per Serving List.”
By contrast, green tea like Issaku Green Tea, one of the premium green teas from Japan, is an excellent source of polyphenols. Other excellent sources of polyphenols include berries, coffee, black tea, dark chocolate, red wine, and artichoke.
