Green Tea (Camellia Sinensis) Ordinary Beverages or Medicinal Beverages: A Review

Tea (Camellia sinensis) is one of the most widely consumed beverages in the world. Tea extracts are source of polyphenols, which are antioxidant components. Green tea phenolic compounds are predominately composed of catechin derivatives, although other compounds such as flavonols and phenolic acids are also present in lower proportion. Camellia sinensis is commonly known as Tea which is most consummated beverage in the world. The diversify properties of the C. sinensis encourage us for new research. There are lots of finding in process on the tea. And there are some positive aspects also found. Present review is an attempt to summarize the various pharmacological effects particularly anti cancer and antioxidant activity may be a powerful tool for future era. In this whole study we can see how much tea is beneficial and may be it will prove a good tool for better treatment option.


Introduction
Tea is one of the most widely consumed beverages in the world. Tea plant Camellia sinensis (family-Theaceae) has been originated from Southeast China, gradually expanded to India, Sri Lanka and further into many tropical and sub-tropical countries. The tea plant is grown in about 30 countries Worldwide. It grows best in tropical and subtropical areas with adequate rainfall, good drainage and slightly acidic soil. There are two varieties of tea. Camellia sinensis var. sinensis (China tea) is grown extensively in China, Japan, and Taiwan, while C. assamica var. assamica (Assam tea) predominates in south and south East Asia, including Malaysia and more recently, Australia [2]. Green tea is widely considered as a health-promoting beverage, and the beneficial effects generally associated with green tea have been attributed to its polyphenol content, particularly to catechins and their antioxidant activity. Green tea contains more catechins than black tea or oolong tea. Catechins are in-vitro and in-vivo strong antioxidants. In addition, its content minerals and Vitamins increase the antioxidant potential of this type of tea. It is a widely used medicinal plant throughout India, China and popular in the various indigenous system of medicine like Ayurveda, Unani and Homoeopathy. Green tea has been consumed in all respective ages in India, China, Japan and Thailand. Green tea is believed to be a potent source of beneficial antioxidants, like that found in fruits and vegetables. Tea is particularly rich in polyphenols, including catechins, theaflavins and thearubigins, which are thought to contribute to the health benefits of tea [22]. Over the past 15-20 years, a number of other research studies have been conducted to determine what health benefits can be attributed to consumption of green tea and its extracts. This research has shown that green tea has a variety of potential health benefits. These benefits include anticarcinogenic, anti-inflammatory, antimicrobial, and antioxidant properties, and benefits in cardiovascular disease and oral health.

Acts as Antioxidant
Green tea is believed to be as a potent source of beneficial antioxidants, like that found in fruits and vegetables. Tea is particularly rich in polyphenols, including catechins, theaflavins and thearubigins, which are thought to contribute to the health benefits of tea. Animal studies offer a unique opportunity to assess the contribution of the antioxidant properties of tea and tea polyphenols to the physiological effects of tea administration in different models of oxidative stress [5]. The leaf boasts the presence of a well-known antioxidant, among which EGCG (epigallocatechin-gallate) as well as other notable healing substances, including fluoride, catechins, and tannins. Many studies have confirmed the free radicles scavenging activity of EGCG in vitro and in vivo. Tea catechins have been found to be better antioxidants than vitamins C and E, tocopherol and carotene. The antioxidant activity of tea polyphenols is not only due to their ability to scavenge superoxide but also due to increased activity of some detoxifying enzymes such as glutathione peroxidase, glutathione reductdase, glutathione-S-transferase, catalase and quinine reductdase in small intestine, liver and lungs. The antioxidant properties of tea may prevent atherosclerosis (i.e., hardening, thickening or loss of elasticity of arteries), particularly coronary artery disease [16].

Oral Health Benefits
During the course of the many research studies done using green tea catechin consumption, it was noticed that the research subjects seemed to have improved oral health after consumption. Research was then launched to focus on the effects of green tea on oral health. Two of the general ways in which green tea consumption helps oral health are due to its anti-inflammatory properties, and antimicrobial activity against mouth flora such as Streptococcus mutans [7,6,1]. The antimicrobial activity may also be responsible for the improvement observed as to bad breath [19].

Antiviral Properties
Tea catechins exhibit a protective effect against human immunodeficiency virus (HIV) infection, partly mediated by inhibiting virions to bind to the target cell surface [4,23]. Kawai et al. investigated the mechanism of the anti-HIV effect of green tea polyphenols and clearly demonstrated that EGCg (but not ECG) directly binds to the cell-surface CD4 molecules [13]. It remains to be seen whether these effects are seen in humans and more studies are needed.

Antimicrobial Properties
A large amount of research has been performed assessing the antimicrobial scope of green tea catechins. Organisms affected by green tea include a large number of Gram-positive and Gram-negative aerobic bacteria, anaerobic bacteria, viruses, fungi, and at least one parasite. Among the antimicrobial mechanisms that have been attributed to green tea are: damage to the bacterial cell membrane, inhibition of bacterial fatty acid synthesis, inhibition of other enzymes (e.g., protein tyrosine kinase, cysteine proteinases, DNA gyrase, ATP synthase), and inhibition of efflux pump activity [21].
Not only do green tea catechins exhibit direct effects on microorganisms, but they also show activities related to the prevention of infection. Studies using mice and ferrets showed that consumption of green tea could inhibit transmission of bacteria and viruses; and studies with humans showed that consumption of green tea resulted in fewer fever illnesses, fewer illnesses with cold or influenza symptoms, and fewer actual infections with Influenza A or B [20].

Arthritis
An antioxidant-rich polyphenolic fraction isolated from green tea has been reported to possess anti-inflammatory properties in laboratory animals [8]. One laboratory study reported positive benefits on collagen-induced arthritis in mice. The mice exhibited a significant reduction in the incidence of arthritis (33%) compared with mice not given green tea polyphenols (50%). Analysis showed a marked reduction in the expression of inflammatory mediators such as cyclooxygenase 2, interferon (IFN)-, and tumor necrosisfactor (TNF) -∝ in the arthritic joints of the mice fed green tea polyphenols. Additionally, total IgG and type II collagen-specific IgG levels were lower in the serum and arthritic joints of the treated mice [8].

Anticariogenic Effects
Human and laboratory studies have supported the use of green tea as a preventative measure in dental caries [17,9]. Salivary amylase hydrolyzes food starch to low molecular weight carbohydrates (maltose) that are easily fermentable. A recent study reported that consumption of tea (black or green) inhibits the release of maltose up to 70% [24]. Black tea was a more potent inhibitor than green tea. Another study reported that a green tea extract was effective in reducing the gingival inflammation caused by periodontal structures such as dentures [1]. An in vitro study reported that a green tea extract strongly inhibited Escherichia coli, Streptococcus salivarius, and Streptococcus mutans [18]. The antibacterial effects of green and black tea extracts were comparable with those of amoxicillin, cephradine, and eugenol.

Ultraviolet Skin Protection
There have been several animal studies that support the use of green tea in the prevention of ultraviolet (UV)-induced skin carcinogenesis and as topical skin protection against UV radiation [3,10,12,15]. Similar results have been reported from in vitro studies on human skin [25]. A recent human study reported that a topical application of EGCg prior to exposure to UV radiation had preventative effects on damage to the skin [11]. A single UV exposure of 4 minimal erythema doses (MED) to human skin was found to increase catalase activity (109-145%) and decrease glutathione peroxidase (GPx) activity (36-54%) and total glutathione (GSH) level (13-36%) at different time points studied. Pretreatment of the skin with EGCg from green tea was found to restore the UV-induced decrease in GSH level and protection of the skin to GPx. Further studies are warranted to elucidate the preventive effects of EGCg against multiple exposures of human skin to UV light.

Conclusions
Human studies suggest that green tea may contribute to a reduction in the risk of cardiovascular disease and some forms of cancer, as well as to the promotion of oral health and other physiological functions such as antihypertensive effect, body weight control, antibacterial and antivirasic activity, bone mineral density increase, antifibrotic properties and neuroprotective power. Increasing interest in its health benefits has led to the inclusion of green tea in the group of beverages with functional properties. Other traditional uses of green tea include treating flatulence (gas), regulating body temperature and blood sugar, promoting digestion and improving mental processes. As an herbal remedy, green tea is often recommended to ease stomach discomfort, vomiting and to stop diarrhea. The antibacterial action of tea is useful in treating infections and wounds. The research interest based on tea components may provide an approach to decrease the incidence of and mortality from various diseases. Overall tea is an affordable beverage of natural origin compared to modern beverages such as soft drinks.