Tea is one of the most popular beverages consumed around the world, with over 300 different kinds of tea; true teas are all derived from Camellia Sinensis, a plant native to China. The many types of teas can generally be divided into 3 types: green tea (non-fermented), oolong tea (semi-fermented), and black tea (fermented). Teas, especially green teas, have mounting evidence for their health benefits; they have been linked with cancer prevention, heart disease prevention, weight loss enhancements, and more. Do you like tea? Here are some good reasons for you to keep on drinking it!
Tea is thought to have been originally consumed around 5000 years ago in China. Later on, still over a thousand years ago, tea was brought over to Japan by Buddhist priests. In 1211 Yeisai, a Japanese Zen priest, published a book named “Kitcha-Yojoki” (tea and health promotion), where the preparation methods and health effects were described. Nowadays, scientific evidence is showing all of the beneficial health effects that were first described in 1211 by Yeisai and more (there’s something to Chinese medicine!). The tea plant is native to south China but is now cultivated in many other locations. The top producers today, in addition to China, are India, Japan, Sri Lanka, Indonesia, and Central African countries. Currently green tea contributes to about 20% (mainly in china and japan) of the tea consumed world-wide, whereas black tea is at about 78% (oolong is about 2%).
So where do all of the health outcomes come from? Many of the health effects are derived from the polyphenols that are present in tea. Catechins are the major polyphenolic compounds in tea and are considered flavonoids. Catechins are made by tea leaves during the day (the rate increases with higher temperatures) and are thought to provide protection to the plant (e.g. natural pesticide). Catechins can be split up into 4 main groups: epigallocatechin 3 gallate (EGCG) (makes up about 59% of total catechins), epigallocatechin (EGC) (about 19%), epicatechin 3 gallate (ECG) (about 13.6%) and epicatechin (EC) (about 6.4%). Epigallocatechin 3 gallate (EGCG) is the most well studied catechin derivative in green tea.
Before jumping into green tea, what about the fully fermented black teas? To make black tea, fresh leaves are crushed, which result in the catechins mixing with plant enzymes. The resulting compounds are theaflavins and thearubigins; these compounds account for up to 60% of the black tea dry weight. While the catechin content of black tea is reduced by fermentation, theaflavins and thearubigins are thought to have positive health effects, including benefits in terms of digestive tract health. Despite the popularity of black teas and the composition heavy in theaflavins and thearubigins, the health effects are still largely unknown. More research is needed to see what else black tea has to offer.
In green tea, fresh leaves are heated, which inactivate other plant enzymes, so that the catechins are stabilized. So why drink green tea? The catechin content (particularily EGCG) is linked to the following (but not limited to): oral health, antibacterial action, antiviral action, anti-odorant, anti-stress, anti-inflammation, anti-cancer (shown in epidemiological, preclinical, and clinical studies), anti-arthritic, anti-metastasis, anti-diabetic, anti-obesity, anti-atherosclerotic, and the list goes on and on . Evidence is accumulating showing that green tea reduces body fat and, when combined with an exercise training program, may increase the rate of fat loss and triacylglyceride level reductions. Green tea may help lower both LDL and total cholesterol as well as lower blood pressure; epidemiological and clinical studies have indicated that green tea reduces risks for heart disease.
Because of all of these positive health outcomes, sales of green tea supplements have shot up in recent years; in 2008, sales accounted for $5.5 million in the U.S.A. While green tea beverages have long been safely consumed, there’s limited research on the safety of green tea supplements. No controlled human intervention studies have reported any adverse health effects to date. However, observational case reports and lab studies have indicated that high doses can cause liver toxicity. The therapeutic index of green tea must be established before supplement health outcomes can be realized and safely prescribed.
The health benefits of drinking green tea are impressive, so why not make it an addition to your daily regime? Tea comes in many flavors and can be quite delicious and fragrant; just head over to your local tea shop and you’ll be impressed with the selection (e.g. David’s tea selection has everything from carrot cake flavored oolong tea to movie night (popcorn!) flavored green tea). Knowing how to prepare your tea is key for optimal enjoyment. Black tea should generally be made using boiling water (4–6 minutes), while oolong tea should be steeped in water just slightly below boiling water (3–4 minutes), and green tea should be steeped in water a bit cooler than that (2–3 minutes). You can enjoy tea hot or iced and sweetened or not sweetened. Milk may also be added to enhance the flavor—it is most typically added to black teas. Clearly, drinking tea is a healthy habit to get into, so drink up and reap all of the many health rewards!
Chen D, Wan S, Yang H, Yaun J, Chan J, Chan T, Ping Q. (2011) EGCG, green tea polyphenols and their synthetic analogs and prodrugs for human cancer prevention and treatment. Adv Clin Chem.53:155-77. Deka A, Vita J. (2011) Tea and Cardiovascular Disease. doi:10.1016/j.phrs.2011.03.009. Hara Y. (2011) Tea catechins and their applications as supplements and pharmaceutics. doi:10.1016/j.phrs.2011.03.018. Johnson R, Bryant S, Huntley A. (2012) Green tea and green tea catechin extracts: an overview of the clinical evidence. doi: 10.1016/j.maturitas.2012.08.008. Norotzki B, Reznick A, Aizenbud D, Levy Y. (2012) Green tea: A promising natural product in oral health. doi:10.1016/j.archoralbio.2011.11.017. Sanga S, Labert J, Ho C, Yang C. (2011) The chemistry and biotransformation of tea constituents. doi:10.1016/j.phrs.2011.02.007. Singh R, Akhtar N, Haqqi T. (2010) Green tea polyphenol epigallocatechin-3-gallate: inflammation and arthritis. doi:10.1016/j.lfs.2010.04.013. Sudathip S, Grove K, Lambert J. (2011) Laboratory Studies on Weight Control and Prevention of Metabolic Syndrome by Green Tea. doi:10.1016/j.phrs.2010.12.013. Suzuki Y, Miyoshi N, Isemura M. (2012) Health-promoting effects of green tea. doi: 10.2183/pjab.88.88. See this and other articles on Jennifer Novakovich’s website JennovaFoodBlog.com