Green Tea is made from 'Camelia Sinesis' plant leaves that have not undergone the same withering and oxidation process used to make black teas. Green Tea originated in China, but its production and manufacturing has spread to many other countries in Asia. Several varieties of green tea exist, which differ substantially based on the variety of Camelia Sinesis used, growing conditions, horticultural methods, producton processing, and time of harvest. Here, we will focus on the health and wellness benefits of green tea with a particular focus on polyphenols (bioactive ingredients).
History of Green Tea: After water, tea is the most frequently consumed beverage worldwide. The tea plant originated in south-west of China and as early as 4000-5000 years ago the Chinese people had become aware that tea could promote health and prevent some human diseases. The tea industry in China was developed during the Tang dynasty (small plantations before 581 A.D.; with growth during 581-618 A.D.) and underwent rapid growth under the Song dynasty (960-1279 A.D.) likely due to the health-promoting effects of tea. Tea had become a necessity of life for all citizens, from high officials, the intellegentsia, and down to the common people.
From there on tea was spread around the world. Today, tea is planed in 60 countries, and people from more than 160 countries have formed the habit of teadrinking. The acceptance for tea by people from different countries and different ethnic groups are by and largely related to its beneficial effects on health.
Traditional Chinese medicine wisdom started to be embraced by modern medicine in the 1980s. This is also the time a general spirit of 'returning to nature', started research on the effective components of tea might prevent or control many important diseases.
In 2013, global production of tea was approximately 1.7 million tonnes, with a forecast to double in volume by 2023. As of 2015, China provides 80% of the world's green tea market.
What makes Tea Healthy? Over the past decade many scientific and medical studies have focused on Green Tea for its long-purported health benefits. There is convincing evidence that tea is a cup of life. It has multiple preventive and therapeutic effects. Tea is an important dietary source of polyphenics, particularly flavanoids. More than 4000 of these flavanoids have been identified and widely distributed amongst plants. The chemcial composition of tea includes polyphenols, alkaloids (caffeine and theobromine), amino acids (mainly L-theamine), carbohydrates, proteins, chlorophyll, volatile compounds, minerals (aluminium, manganese and fluoride) and other unidentified compounds (currently being discovered and/or researched by scientists).
Many of these compounds are also found in other natural whole foods but, we simply don't eat enough quantity to reap the benefits. An easier way is to drink a few cups of tea throughout the day and load up on containing bio-active compounds.
Tea Polyphenols: Polyphenols are one of the main bio-active compounds in tea, the major one being flaven-2-ols or, catenchins. Tea catechins are major sites for antioxidant reactions and activity, and stabilise free radicals (ROS). Tea polyphenols prevent the formation of reactive oxygen spices (ROS) and are strong metal ion chelators.
Popular and studied catenchins (flavan-2-ols) in Green Tea include:
(1). epicatchin (EC),
(2). epicatechin-3-gallate (ECG),
(3). epigallocatechin (EGC), and
(4). epigallocatechin-3-gallate (EGCG).
These flavanoids and other polyphenols present in tea have shown a wide range of biological and pharmaceutical benefits, including prevention of cancer, obesity, Type-2 Diabetes, depressive symptoms, cardio-vascular diseases and cerebral ischemic damage. Further, tea possesses insulin-enhancing, antioxidative, hypolipidemic, anti-microbial, immune-stimulatory, anti-inflammatory, neuro-protective and bone enhancement activities.
A point to note is that after drinking tea only a certain percentage of the polyphenols are absorbed, with those appearing in the blood and tissues considered bio-available the rest are discarded as waste product. Henceforth, the research shows tea consumption is directly related to health benefits, the more tea consumed, the more health benefits noted.
Cancer Prevention Benefits: Green Tea and its major components, such as tea polyphenols, catechins and caffeine administered through drinking water or diet have been demonstrated to inhibit tumorigenesis in many animal models for different organ sites, including the lung, oral cavity, oesophagus, stomach, small intestine, colon, skin, liver, pancreas, bladder, prostate, and mammary glands.
Data at a glance:
(1). Tea and tea polyphenols have been shown to inhibit tumour formation and growth in different animal models for human cancer. The inhibition is associated with decreased cell proliferation, increased apoptosis and suppression of angiogenesis.
(2). Tea polyphenols are antioxidants, but they can also generate reactive oxygen species. The major polyphenol from Green Tea, epigallocatechin-3-gallate, has shown to bind directly to several receptors and signalling molecules, and to inhibit the functions of key receptors, kineses, proteinases and other enzymes.
(3). Epidemiological studies however, have not yielded conclusive results on the cancer-preventive effect of tea consumption in humans, possibly owing to different confounding factors. Some human cancer prevention trials with green tea polyphenol preparations have shown promising results.
(4). Well-designed epidemiological studies and intervention trials are needed to evaluate the cancer-preventive activities of tea and tea polyphenols in humans.
(5). Many issues raised and the experience gained from studies on tea and cancer prevention may be applicable to studies on other dietary constituents.
Overall, cancer prevention by tea and tea components has been studied in many different animal models of carcinogenesis. In a review of 147 papers published up to December 2008, 133 described cancer-prevention or inhibitory effects.
For human subjects, a review on 127 case-control studies and 90 cohort studies on the relationship between tea consumption and the risk of certain cancers was done. Of these 51 case-control and 19 cohort studies showed an inverse association between tea consumption and cancer risk, whereas other studies showed no such association. Scientists attribute this inconsistency in data due to different factors, such as difficulty in quantifying tea consumption, varied cancer origin and factors, and population diversity. Overall, the scientists state, when these variables were effectively managed, a clearer relationship between tea consumption and cancer risk was observed in several studies.
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