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Green Tea is Beneficial for a Number of Reasons

Tea is the second most widely consumed beverage in the world behind water. Originating in China, tea have played an economic and social role as a popular daily beverage as well as a medicinal drink. For centuries, the Chinese have used green tea as a therapeutic tool because of the belief that it contains medicinal properties. Based on recent animal and human studies, some evidence has accumulated that indeed, tea may provide some health benefits.

There are many different types of tea; black tea, white tea, green, and herbal teas, to name a few. Black, oolong, and green tea all come from the same plant, the Camellia sinensis plant. Teas are generally classified based on how the tea is fermented. Black and red teas are fermented, oolong tea is semi-fermented and green tea is not fermented. Non-fermented teas such as green tea, are produced when fresh picked leaves are dried and steamed; semi-fermented tea is produced when the fresh leaves are partially fermented before drying; lastly, black and red teas are fermented after harvesting before the drying and steaming process (Cabrera et al., 2006).

Black tea is the primary tea produced and consumed worldwide (76-78%), followed by green tea (20-22%), with oolong tea the least common (2%). Green tea is most popular in China and Japan while Americans primarily drink black tea.

Green tea has received a lot of attention in the past few decades due to it’s reported medicinal properties. Green tea contains several amino acids, carbohydrates, lipids, vitamins and minerals. However, the constituent that has received the most press is the polyphenols found in the green tea leaf. Polyphenols are a broad class of anti-oxidants that includes flavonoids and catechins. There are reportedly 12 types of flavonoids, including the catechins. These are the substances that have been associated with anti-carcinogenic, anti-viral, and anti-inflammatory properties. While all teas contain polyphenols, green tea has a higher concentration of catechins.

There are 4 major catechins: epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and epicatechin (EC). EGCG (59%) is the major catechin followed by EGC (19), ECG (13.6%), and EC (~6.4%) (Cabrera et al., 2006). Catechins, particularly EGCG, are thought to have anti-oxidants properties greater than vitamin C, E or A Antioxidants are beneficial in their role of quenching the free radicals that can damage healthy cells and DNA leading to heart disease, cancer, strokes, etc.
Green tea also contains a number of other flavonoids such as gallic acid which also provide antioxidant and anti-inflammatory benefits.

The catechin content varies depending on how the leaves are processed before drying, soil, climate, fertilizers, brew time, temperature, and type of green tea (decaffeinated, instant, blended, etc). Decaffeinated, instant products, and ready-to-drink commercially available beverages also have lower amounts of catechins. Because black and oolong teas are fermented, the EGCG content also tends to be lower compared with green tea.
 Epidemiologic, animal and in vitro laboratory studies have found that the consumption of green tea may provide chemopreventive benefits. Some clinical data shows that green tea possesses antimtagenic and anticarcinogenic activity, inhibits cancer cell growth in tumor cell cultures and animal tumor models. Wu et al. found a significant reduction in the risk of breast cancer in women who drank green tea at least twice a day or greater compared to women who drank 0-1 cups/d (Wu et al., 2003).  Additionally, others have reported a lower risk of recurrence in women with stage I or II breast cancer (Inoue et al., 2001). Risk of breast cancer has not been related to herbal tea, black tea, or any type of coffee.
Other clinical studies have found that green tea may reduce the risk for ovarian cancer, lung cancer in non-smoking women, and prostate cancer (). Green tea consumption has not been associated with a beneficial effect for reducing gastric, stomach, colon, or bladder cancers.

 In some human epidemiological studies, the regular consumption of green tea is associated with a protection against the development of dental caries. The results of both In vitro and in vivo animal and human studies suggest that green tea polypenols may prevent solar UVB light-induced skin conditions such as melanoma and non-melanoma skin cancers (Katiyar, 2003). Additionally, green tea may also play a role as a functional food in weight control. Wu et al. reported that an inverse relationship may exist among individual who regularly consume green tea and percentage of body fat, and body fat distribution (Wu et al., 2003). Lastly, green tea may offer neuroprotective benefits against neurodegenerative conditions such as Alzheimers and Parkinsons disease (Cabrera et al., 2006).

Non-decaffeinated green tea contains caffeine, therefore insomnia is one of the negative side-effects associated with large amounts of green tea consumption. Green tea contains approximately 30-60 mg/6-8 ounces of tea; a lot less than coffee.

Summary

In conclusion, green tea has been used since ancient times as both an everyday beverage to drink, and for its medicinal properties. Regular green tea consumption reportedly may reduce the risk for certain types of cancer, hypertension, heart disease, dental caries and other common medical conditions. However, to gain the purported multitude of benefits related to drinking green tea, the caveat is drinking at least 4-5 cups daily. Green tea is generally considered tasty, affordable, and available. While green tea consumption has been associated with a wide range of benefits, less is known about dietary supplement capsules with green tea extract. More research is needed regarding the safety and efficacy of these products before recommendations regarding their use on a regular basis can be made. Since green tea as a beverage may provide a wealth of benefits compared to other commonly consumed beverages in the U.S., such as coffee, soda, and alcohol, it seems worthy to consider the addition of green tea to the list of beverages that should be consumed daily!

References:

Cabrera C, et al. Beneficial effects of green tea – A review. J Am Coll Nutrition 2006;25:79-99.

Katiyar SK. Skin photo protection by green tea: Antioxidant and immunomodulation effects. Curr Drug Targets 2003;3:234-242.

Wu CH, et al. Relationship among habitual tea consumption, percent body fat, and body fat distribution. Obes Res 2003a;11:1088-1095.

Wu AH, et al. Green tea and risk of breast cancer in Asian Americans. Int J Cancer 106;574-579.

Inoue M,, et al. The risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett 2001;167:175-182.