Review Article

DOI: 10.17354/cr/2015/92

Green tea- A Healthy sip Bellona Thiyam1, S V Ravindra2, M Parvathi Devi3, Garima Yeluri4, Akshatha Gadiyar5 Post-graduate Student, Department of Oral Medicine and Radiology, Teerthanker Mahaveer Dental College and Research Centre, Moradabad, Uttar Pradesh, India, 2Reader, Department of Oral Medicine and Radiology, Teerthanker Mahaveer Dental College and Research Centre, Moradabad, Uttar Pradesh, India, 3Professor and Head, Department of Oral Medicine and Radiology, Teerthanker Mahaveer Dental College and Research Centre, Moradabad, Uttar Pradesh, India, 4Senior Lecturer, Department of Oral Medicine and Radiology, Teerthanker Mahaveer Dental College and Research Centre, Moradabad, Uttar Pradesh, India, 5Post-graduate Student, Department of Public Health Dentistry, KLE VK Institute of Dental Sciences, Belgaum, Karnataka, India 1

After water, tea is the most consumed popular drink in the world. Green tea which is a leading beverage in the Far East for thousands of years is regarded as a health product. It is nothing but a non-fermented tea which contains more catechins, than black tea or oolong tea. Catechins are strong antioxidants with its additional content of certain minerals and vitamins increasing its antioxidant potential. High-molecular-weight polyphenols isolated from green tea which includesepigallocatechin 3 gallate (EGCG) constitute the most interesting components in green tea leaves. The aqueous extract or the major polyphenols of green tea possess cariostatic, antimutagenic, antidiabetic, antioxidant, antibacterial, anti
inflammatory, antitumor, hypocholesterolemic, as well as cancer-preventive activities in a variety of experimental animal models system and have been demonstrated in various studies Keywords: ggreen tea, antioxidant, EGCG, oral health

INTRODUCTION Nowadays, many people all around the world are turning to the nature by using natural herbal products for both prophylaxes and treatment of different diseases. The interest in naturally derived biologically activecompounds that may have potential therapeutic uses in medicine and dentistry is rising.1 Forthousands of years, plants have been used in folk medicine and although with the development of modern medicine, the basisfor development of many new lead chemicals for pharmaceuticals products are still derived from medicinal plants. Evidence showsthat2 dental medicine has become especially amenable toplant-derived products andregularly incorporate foods or beverages containingcertain phytochemicals into their diet to yield be er oral health.1,3 Tea being one of the most widely consumed beverages in the world, is next to waterand as compared to coffee, beer, wine and carbonated soft drinks.4 The tea plant, Camellia sinensis, Access this article online Month of Submission Month of Peer Review Month of Acceptance Month of Publishing

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is a member of the Theaceae family. It is an evergreen shrubthat can grow to heights of 30 feet, but is usually pruned to 2-5 feet for cultivation. The leaves are dark green in color, alternate and oval in shape, with serrated edges, and the blossoms are white, fragrant, and they appear in clusters or singly.3 Based on the level of fermentation,it can be categorized into three types, i.e., green (unfermented), oolong (partially fermented) and black (fermented) tea. The term fermentation is an inappropriate word to be used in tea processing, oxidationshould be a more appropriate term, which means exposing the leaves to air while drying without any additives during the process. White tea is another form of tea available which is made from new growth buds and young leaves that have been steamed so as to inactivateoxidation of polyphenol and then dried. Inorder to prevent formation of chlorophyll, the buds may be shielded from sunlight.4

HISTORY The use of tea leaves probably first originatedmore than 3,000 years ago, in the southwest area of China and initially was used by people only for chewing and eating, in just the same way that coffee was first used. At that time people were eating the coffee beans directly in Ethiopia. Over time, people began to use in cooking and when added to boiling water to flavor the water they drunk, the use of leaves and

Corresponding Author: Dr. Bellona Thiyam, Teerthanker Mahaveer Dental College and Research Centre, Moradabad, Uttar Pradesh, India. Phone: +91-8126706953. E-mail: [email protected]

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buds from the tea plants gradually expanded.5During the 8th century, the method of steaming the leaves to inhibit their oxidation was first discovered and the history of green tea too starts from here. A new frying method of “fixing” the leaves was then introduced in the 12th century. The process of steaming and fixing of the leaves resulted in teas that have the characteristic un-oxidized taste and appearance to modern green teas, and both processes are still followed today.6 Varieties of green tea were introduced as they were discovered, over the centuries. With green tea development,Oolong and black tea were created much later. The fermented version of green tea is Black tea and Oolong is semi fermented. Althoughfor many centuries, green tea was not as popular in the western world as black tea, it spread throughout the globe and became a much sought after commodity. As they delve into the secrets and customs of the Eastern world - the land that created the sensation, the western world is still in the process of discovering the varieties of delicious green tea and other types of tea.7 Composition of Green Tea The chemical composition of green tea varies with climate, season, horticultural practicesand position of the leaf on the harvested shoot.8 The main components of green tea which play the major role are thepolyphenols, which are flavonoids. The four major flavonoidsin green tea are the catechins, epicatechin (EC), epigallocatechin (EGC), epicatechingallate (ECG) and epigallocatechingallate (EGCG) (Figure 1).1,2,3,6 Epigallocatechingallate is the most significant active component in green tea. The leaf bud and first leaves are richest in EGCG. Dried green tea leaves contain 8–12%of total polyphenols.The chemical composition of green tea includes: proteins (15-20% dry weight), whose enzymes constitute an important fraction; amino acids (1-4% dry weight) such as theanine or 5-N-ethylglutamine, glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, and lysine; carbohydrates (5-7% dry weight) such as cellulose, pectins, glucose, fructose, and sucrose; minerals and trace elements (5% dry weight) such as calcium, magnesium, chromium, manganese, iron, copper, zinc, molybdenum, selenium,sodium, phosphorus, cobalt, strontium, nickel,

Figure 1: Major polyphenols in green

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potassium, fluorine, and aluminum; and trace amounts of lipids (linoleic and α-linolenic acids), sterols (stigmasterol), vitamins (B, C, E), pigments (chlorophyll, carotenoids), and volatile compounds (aldehydes, alcohols, esters, lactones, hydrocarbons). The fresh leaves contain, on average, 3-4% of alkaloids known as methylxanthines, such as caffeine, theobromine, and theophylline.9 Green tea also constitutesan important source of antioxidants, such as carotenoids, tocopherols (vitamin E derivatives) and vitamin C which is also present in fruits and vegetables.10 Tea also contains minerals like zinc, selenium and manganese that function as co-factors in antioxidant enzymes.11 Mechanism of action The retardation of the growth and development of neoplasms byinhibition of tumor initiation and promotion, induction of apoptosis, and inhibition of cell replication rates is due to the anticarcinogenic properties of green tea polyphenols.12 The polyphenols antioxidant potential of green tea is directly related to the combination of aromatic rings andhydroxyl groups that make up their structure and is a result of binding and neutralization offree radicals by the hydroxyl groups. In addition, the activity of hepatic detoxification enzymes is stimulated by green tea polyphenols, thereby promoting detoxification of xenobiotic compounds and are also capable of chelating metal ions, such as iron, that can generate radical oxygen species.The production of arachidonic acid metabolites such as pro-inflammatory prostaglandins and leukotrienes is inhibited bygreen tea polyphenols, which results in a decreased inflammatory response. EGCG has the ability to block inflammatory responses to ultraviolet A and B radiation, as well as, significantly inhibiting neutrophil migration that occurs during the inflammatory processand this has beendemonstrated by human and animal studies. There exists a synergistic interaction between green teas caffeine content and catechin polyphenols that can result in prolonged stimulation of thermogenesis. Studies have also shown green tea extracts are capable of reducing fat digestion by inhibiting the activity of certain digestive enzymes.8,9 Although the exact mechanism is unknown, green tea catechins have been shown to significantly raise levels of Lactobacilli and Bifidobacteria while at the same time decreasing the levels of numerous potential pathogens. Green tea demonstrates antibacterial properties against a variety of gram-positive and gram-negative species.13 Other than acting as antioxidants, polyphenols have additional mechanisms in which they reduce oxidation level: (1) It binds metal ions such as iron and copper and prevents their participation in oxidation reactions, forming hydroxyl radical. (2) Prevents redox sensitive transcription factors activation that amongst others things serve as mediators of inflammatory reactions. (3) Suppresses oxidation

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stimulants such as induced nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), lipoxygenase 2 (LOX-2) and xanthine oxidase.(4) Induction of antioxidant enzymes like glutathione S-transferase and super oxide dismutase.10 Preparation of green tea A ceramic teapot is prepared by warming it with hot water. For the teapreparation, use fresh, cold water, filtered or from a spring, if possible, instead of a tap water. After the water is boiled, let it cool for three minutesso that temperature of the water is 80 degrees centigrate. The teapot is covered for three more minutes after the hot water is poured over the tea leaves, after which it is let to steep. Since lemon is rich in vitamin C, which protects the polyphenols from being oxidized and lost, squeezing some of it helps. Honey, sugar or milk can be added for flavour according to ones taste.14 Purdue University polyphenols researcher Mario Ferruzzi recommends to consume enough of the tea polyphenols and consume them often enough, that means three servings a day so as to keep their levels in the blood high15 (Figure 2).

ORAL HEALTH BENEFITS Dental caries Various factors like diet, nutrition, the resident oral flora and the host response interact to determine whether infection occurs in a multi factorial condition like dental caries. Any intervention in any of the factors that can reduce its incidence will have a significant impact on public health. Caries can be generally prevented by cleaning teeth. There are reports that tea consumption may decrease dental caries in laboratory animals and humans.Magalhaes et al. found thaterosion and abrasion of teeth can be protected by mouth rinsing with green tea extract (0.61%)16. In addition, washing mouth with green tea (1.6 g of pulverised green tea in 40 ml for 3 times a day) for a week was able to significantly reduce the salivary levels of the virulent cariogenic pathogens, Streptococcus mutans and lactobacilli. Such reduction of those pathogens level will decrease the susceptibility to dental caries. Zhang et al. showed that tea extract reduced amylase activity in human saliva. Therefore, tea consumption is likely to be an anti-cariogenic agent which lessens the cariogenic potential of starch containing foods, that leads to less maltose release that causes mineral depletion from tooth enamel.7,8,9 Enough evidences have been collected which shows that the bioactive components of green tea are able to influence

the process of caries formation at several different stages: by inhibiting proliferation of the streptococcal agent, by interfering with the process of adhesion to tooth enamel or by acting as inhibitors of glucosyltransferase and amylase. Catechins in green tea are inhibitory for S. mutansand S. Sobrinus with 50 and 1000 μg/ml, well within the concentrations found in brewed tea have been reported by many workers.8 The polyphenolcomponents in the extracts obtained from different teas, affect caries development as they reduce the production of acidic compounds and synthesizestreptococci to adherent water-insoluble glucan from sucrose with the cooperative action of glucosyltransferase. Kubo et al. found that many of the ‘flavourcompounds’ (e.g. nerolidol) are present in low concentration in green tea. But theymight give synergistic effect with the abundant catechins. There is good experimental evidence that catechinscan prevent the a achment of oral streptococcal pathogens to surfaces. Otake et al.in their study, found tha he a achment of Streptococcus mutansto saliva-coated hydroxyapatite discsis prevented by Sunphenon (a commercial mixture of catechins extracted from green tea leaf) andhave demonstrated that EGCG and ECG inhibit streptococcal glucosyltransferase, while Kashket et al.found the effective inhibitors of the enzymeto becatechin fraction of tea and other beverages.9 Abolition of halitosis The main reason for halitosis is dental caries and periodontal diseases. Volatile sulphur compounds such as H2S and CH3SH that is produced by decay processes that are created by oral microorganisms causes bacterial halitosis. Lodhia et al. found thathalitosis could be prevented for an hour by green tea powder which succeeded to abate the creation of those sulphur compounds.8 Zeng et al. were able to demonstrate that green tea extract was able to remove the odorant sulphurs.Accordingly, some of the bad breath treatment products such aschewing gum and mouth spray contain tea polyphenols.The study conducted by KushiyamaMitosi et al analyzed the periodontal health of 940 men, and found that those who regularly drink green tea had superior periodontal health.7AbdolhoseinMoghbel et al(2011) conducted a study on the effect of green tea on prevention of halitosis, and plaque formation on teeth in 25 volunteerswith mouthwashes containing 0.2, 0.5, and 1% tannin, as the most effective antibacterial complex in green tea. Then they compared a green tea mouthwash containing 1% tannin with 10% ethanol, an alcohol free

Figure 2: Preparation of green tea

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mouthwash and a green tea herbal mouthwash with a chlorhexidine 0.2% sample and reportedthat the herbal green tea mouthwash could prevent plaque formation on teeth and overcome halitosis due to infection of the bacteria by reducing the aerobic bacterial load. Also, it is a safe and nontoxic mouthwash especially for children and pregnant women.8.10 Antioxidant potential Green tea protects cells against the damaging effects of reactive oxygen species, such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals, and peroxynitrite by acting as an antioxidant along with polyphenols.11 Cellular damage is due to the oxidative stress which is caused due to an imbalance between antioxidants and reactive oxygen species. Tea polyphenols have the ability to scavenge reactive oxygen species (ROS), which are known as “free radicals,” and nitrogen species.7,8 ROS and nitrogen species are known to a ack the lipid membranes and damage cell DNA. Antioxidants can deactivate or destroy ROS, hence preventing them from damaging cells. Although the antioxidant capacity of catechins determined in vitrois dependent upon the type of assay employed, factors such as bioavailability and metabolism are not reflected. Catechins are rapidly and extensively metabolized and this emphasizesthe importance of demonstrating their antioxidant activityin vivo to be er represent the physiological impact of green teaconsumption.10 Anti-carcinogenic property Many of the studies which were investigated by green tea extracts or EGCG on animalsusing biomarkers associated with cancer risk or development reported that green tea extracts or EGCG protected against chemical carcinogens in several organs such as intestine, lung, liver, prostate, breast and mouth. Lifestyle related diseases which also includes cancer, are also characterizedas aging-related diseases which is also one of the major factors. Therefore, slowing the aging process and avoiding theclinical appearance of the disease will prevent lifestyle-related diseases. Several population-based studies have reported the cancer-protective effects of green tea. For example,in countries such as Japan where green tea is regularly consumed, cancer rates tend to be low. It is not possible to come to conclusion from these population-based studieswhether green tea actually helps in preventing cancer in people. However, numerous emerging animal andclinical studies are beginning to suggest that EGCG may play an important role in the prevention of cancer.17 EGCG inhibits the release of tumour necrosis factor-alpha which stimulates tumour promotion and progression of initiated cells as well as pre-malignant cellsand tumour growth is suppressed by other tea catechins[12]. Furthermore, EGCG was shown to reduce specific binding of both the

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12-Otetradecanoylphorbol-1-3-acetate (TPA) type and the okadaic acid-type tumourpromoters to their receptors. The interaction with the phospholipid bilayer of thecell membrane results in the ‘sealing’ effect of EGCG [13]. Based on thevariousinvitro, in vivo and epidemiological studies, green tea is today, accepted as a cancer preventive.14 An oral dose of green tea were given to hamsters with buccalpouch tumour that was induced by 7,12-dimethylbenz (a) anthracene (DMBA) before and until the end of the experiment. When compared to controls, pathological changes decreased andoral malignant tumours were smaller.In rats, oral cancerwas induced by 4-Nitroquinoline 1-oxide (4-NQO) and they were given green tea polyphenols extracts. Rats that did not receive green tea had larger number andvolume of tumours.13 Antiviral properties The enzymes that damage cellular membranes are inhibited and prevented frombinding and penetration of viruses to cells by the polyphenols contain in the green tea which acts as antioxidantsand hence green tea is also known for its antiviral properties.In vitro studies have shown that bya aching to viral haemagglutinin and preventing its a achmen o cellular target receptors, EGCG which is present in green tea prevents infection from influenza virus.Furthermore, there isevidence which shows that themechanism of Human immunodeficiency virus type 1 (HIV-1), Herpes simplex virus (HSV-1), Epstein Barr virus, adenovirusesand more is interfered by green tea.13 Anti-Hypertensive Effect and Cardiovascular Disease Risk It has long been believed in popular Chinese medicine that green tea possesses hypotensiveeffects. 18 Negishi et al.observedthat both black and green tea polyphenols a enuateblood pressure increase, with the help of their antioxidant properties,in stroke-prone spontaneously hypertensive rats, but he used approx. 1L of tea. 16 Recently, some epidemiologicalstudies indicated that green tea consumption slightly reducesblood pressure.10,11 Yang et al. concluded in their study that the risk of developinghypertension in the Chinese population is reduced by habitual moderate strength green tea or oolong tea consumption, 120 mL/day or more for 1 year. The collaboration of American researchers with their Chinese counterparts todiscuss the beneficial effects of green tea diet on cholesterol levels was published in the Archives ofInternal Medicine. 240 men andwomen (average age 55 years) who possessed mild-to-moderately high LDL cholesterollevels were taken in the study and were instructed t to retain their usual low-fat diet, green tea diet intakeand activity levels. After 12 weeks,loss of more than 15% of their total LDL cholesterol levelswas seen in those who consumed green tea dietextract along with their regular meals.15 The amount of cholesterol absorbed

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by the body is reduced by certain compounds in green tea by increasing the amount of cholesterolexcreted and thus keeping cholesterol from being stored in the liver as shown by certain studies. The antioxidant properties of green teamay help prevent atherosclerosis, particularly coronary artery disease as indicated by many population-based and clinical studies. According toJapanese research, green tea reduces the levels of LDL cholesterol and hence reduces therisk of coronary heart disease.1,5,7 Effects on absorption of metal ions Green tea catechins have the potential toaffect absorption and metabolism of ions since the flavonoids have the capability tointeract with a variety of metal ions. Thesecatechins can affect iron absorption, particularly ingroups who are at risk of iron deficiency, but their effectson other ions are less understood. While green tea ingestionover a long period does not affect the apparentabsorption of copper, it decreases the absorption of zincand increases that of manganese. However, there are no evidences which show that catechinintake affect the plasma concentration of these ions. 12 Effects on carbohydrate metabolism In Type II diabetes, which is a heterogeneous disorder,there is resistance of glucose and lipid metabolism in peripheral tissues to the biological activity of insulin and insulin secretion by pancreatic β cells is inadequate. In a study by Sabu et al. (2002), he administered GTPs (500 mg/kg) to normal rats and found increase in glucose tolerance significantly at 60 minutes. Serum glucose levels was also reduced in alloxan diabetic rats at a dose of 100 mg/kg. For 15 days he continued the administrationof the green tea extract at 50 or 100 mg/kgdaily and it produced 29% and 44% reduction, respectively, in the elevated serum glucose level produced by alloxan administration.13 Neurodegenerative Diseases It is believed that the major contributor to the pathogenesis of Parkinson’s disease is said to be oxidative stress, especially the death of dopaminergic neurons. Recently, misregulated iron metabolism in the brain has also been implicated as one of the potential contributor. Several studies conducted using green tea have given positive results by showing significant protection against the development of Parkinsons disease. The antioxidant and iron-chealating properties of EGCG was believed to be the protective agent responsible for these results.3,4,9 Many studies on laboratory animals and cell cultures have suggested that EGCG may delay Alzheimer’s disease.19 Side effects of Green tea. Although green tea is a beneficial natural product for health, its effects and constituents may be beneficial up

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to a certain dose only. But some unknown adverse effects may be caused with higher doses. Moreover, the effects of green tea catechinsmay differ from an individual to individual.20 The only negative side effect reported so far from drinking green tea is ‘insomnia’ because of its caffeine content. However, green tea contains less caffeine compared to coffee: thereare, 30–60mg of caffeine in 6–8 ounces of tea, compared to over 100 mg in 8 ounces of coffee. Patients sensitive to caffeine shouldbe advised to use caffeine-free green tea or a caffeine-free extract.13Green tea contains vitamin K which may interfere with warfarin. In general, the level of fluoride in tea is inversely related to the EGCG contents, which means that the morenatural EGCG in the tea leaves, the less is the fluoride content. Decaffeinated teas, whencompared to their caffeinated counterparts, have aneven higher fluoride content. According to Andreas Schuld of the Canadian ‘Parents of Fluoride Poisoned Children’, fluoride is considered a cancer promotoras it could possibly reduce the anti-cancer properties of tea or even cause cancer. The high fluoride content in green tea could also cause neurological and renal damage,especially in the presence of aluminium. In addition, the high fluoride content could causeosteoporosis, arthritis and other bone disorders.2But based on the current literature, there does not appear to be any significant side effects ortoxicity which may be caused due to regular green tea consumption. However patient should be aware of his general health and the side effects of the green tea before starting the green tea consumption.

CONCLUSION Green tea is consumed all over the world in various forms. The years of safe consumption of this beverage, supported by numerous studies showing health benefits,warrant a general recommendation to consume it on regular basis. Nowadays, green tea is being studied extensively worldwide as it isconsidered as one of the most promising dietary agents for the prevention and treatment ofmany diseases. Numerous studies show that aqueous extract of themajor GTP designed as catechins (EGCG, EGC, ECG and EC)possess antioxidant, antimutagenic, antidiabetic, anti-inflammatory, antibacterial and antiviral, and above all, cancer-preventive properties. This reviewpresents various studies supporting green tea’s role in maintaining oral health as well as the general health. But further research on this field is still needed to define the actual magnitudeof health benefits, so that the mechanisms of action can be elucidated, to establish thesafe range of tea consumption associated with these benefits and to advocate for green tea for prevention and treatment of specific oral as well as health morbidities. The developing biomarkers for green tea consumption, as well as molecular markers for its biological effects, will facilitate future research in this area.

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But there seems to be no reason not to include green tea in our everyday sip.

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How to cite this article: Thiyam B, Ravindra SV, Devi MP, Yeluri G, Gadiyar A. Green Tea - A Healthy Sip. IJSS Case Reports & Reviews 2015;1(12):55-60. Source of Support: Nil, Conflict of Interest: None declared.

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