Green Tea; Nutritional Value, Uses, Health Benefits

LC: Langerhans cells; LPO: lipid peroxidase; MAPK: mitogen-activated protein kinase; NOS: nitric oxide synthase.

• Therapeutic Effects on Periodontal and Gingival Health – The gingival crevice is a physiological zone surrounded by gingiva and tooth margins. A colony of microorganisms resides in this space and most common of that are anaerobes. In pathological conditions, these spaces extend and periodontal pockets filled with serum exudates and large colonies of polymorphs. Additionally, oxidative stress supports the development of diseased conditions. The microbes commonly present in such conditions are Prevotella spp and Porphyromonas gingivalis (black pigmented anaerobes) [23]. Periodontal health is inversely related to consumption of green tea, an epidemiological study proves that people have better periodontal health if they drink green tea very often for example during meals or at breaks from work [24]. Green tea plays a supportive role in the maintenance of periodontal health, as suggested by an in vitro study catechins (e.g. EGCG) restrict the development and colonization of harmful bacteria such as Porphyromonas gingivalis, Prevotella intermedia, and Prevotella nigrescens [25]. These bacteria cause severe harm to periodontal tissues for example Porphyromonas gingivalis develop adhesion to buccal mucosa and cause destruction [26]. Recently, Nadeem et al. [27] studied the influence of green tea consumption versus black tea on periodontal health of 240 dental students and noticed that students who were consuming green tea had good periodontal health status with minimal plaque accumulation in comparison with consumers of black tea. Literature exhibited that better periodontal health status of regular green tea using individuals is mainly due to catechins, as these are steric structures of 3-galloyl radial, ECG, EGCG and gallocatechin gallate (GCG) (major polyphenols) and responsible for restrain release of toxic end metabolites from Porphyromonas gingivalis [28].
• Lowering Your Risk of Alzheimer’s and Parkinson’s – Not only can green tea improve brain function in the short term, but it may also protect your brain in old age. Alzheimer’s disease is the most common neurodegenerative disease in humans and a leading cause of dementia. Parkinson’s disease is the second most common neurodegenerative disease and involves the death of dopamine-producing neurons in the brain. Multiple studies show that the catechin compounds in green tea can have various protective effects on neurons in test tubes and animal models, potentially lowering the risk of Alzheimer’s and Parkinson’s [29, 30].
• Help in  Dental Caries – Dental carries is a pathological condition resulting due to demineralization of tooth structure because of bacterial infections and/or deficiency of nutrients. Oral microbes are responsible for carries development, out of which mainly streptococcus mutants are most active [31]. The oral antimicrobial peptides are known to reduce the bacterial activity [32]. Green tea leaves are known to be rich in fluoride and other components such as polyphenols (catechins) that play a supportive role in resisting dental carried as reported in many studies [33, 34]. The beneficial role of fluoride is well known as it inhibits the bacterial growth and helps re-mineralization of dental tissues [,35]. Cariogenic bacteria release glucans with the help of glucosyltransferase (GTase) which are branched and facilitate adherence of microbes to tooth surface [36]. GC and EGC are the catechins that restrict the growth of 10 types of carries causing bacteria. Otake et al. [37] showed that total amount of catechins, mainly EGCG and its epimer gallocatechin, EC and ECG present in one cup of green tea prevent streptococcus mutants from adhering to tooth surfaces. The catechins were extracted from green tea with concentration of 100mg/L and their effects on bacterial adhesion to salivary coated hydroxyapatites were observed. Other studies also exhibit that consumption of tea constrains the release of the salivary enzyme, amylase as observed by Kashket and Paolino [38]. Later it was supported by Zhang and Kashket [39] proving that tea, either black or green restrains the enzymatic activity of Streptococcus mutans’ amylase on tooth structure preventing deminerlization.
• Bad Breath (halitosis) Reducer – The main reagents responsible for halitosis (bad breath) are volatile sulfide compounds such as hydrogen sulfide (H₂S), dimethylsulfide [(CH₃)₂S] and methyl mercaptan (CH₃SH). These reagents degrade in the oral cavity by proteolytic reactions primarily by anaerobic gram negative bacteria consuming numerous sulfur-containing substrates including saliva, food debris, epithelial cells and blood [40]. Green tea is well known for antibacterial properties against anaerobic microorganisms. Green tea can abolish bad breath by suppressing anaerobic bacteria and eliminating the production of volatile sulfur compounds [41]. Deodorant action of ingredients decreases in the following order: EGCG > EGC > ECG > EC. The deodorizing action of EGCG is based on a chemical reaction of EGCG and MSH and introducing methylsulfinyl/methylthio group into the B ring of EGCG. During this reaction, a methylthio group is supplemented in the orthoquinone form of the catechin produced by oxidation, hence eliminating the halitosis [45].
• Anti-Platelet Activity and Anti-Thrombotic Effect – Platelet activation and aggregation also play an integral role in the development of CVD. The alterations in platelet sensitivity and platelets-vessel wall interaction are associated with the development of cardiovascular events. In the presence of vascular endothelial injury, platelets rapidly aggregate to form hemostatic plugs and arterial thrombi which could trigger the acute vascular events such as myocardial infarction [42]. Indeed, there is extensive evidence that anti-platelet therapy can reduce CVD risk [43].
• Cure Fever  – The effectiveness of green tea in treating any type of diarrhea and typhoid has been known in Asia since ancient times [44–45]. Green tea catechins have an inhibitory effect on Helicobacter pylori infection [46,47]. Effects of green tea against the influenza virus, especially in its earliest stage, as well as against the Herpes simplex virus have also been demonstrated [48]. Furthermore, Weber et al. [49] observed that adenovirus infection is inhibited in vitro by green tea catechins.
• Cigarette Smoke Induced Inflammation – Smoking affects the homeostasis and injurious to oral health [50]. The effects of smoking range from simple mucosal erythema to premalignant conditions and oral cancer. Smoking intensifies oral malignancies in response to oral inflammatory diseases due to the compromised status of salivary antioxidants [51]. Diminished activity of numerous salivary enzymes is observed during smoking hence compromising the protection against oxidative damage [52]. In addition, smoke coming from tobacco comprised of reactive oxygen species (ROS) including superoxides, hydroxyl radical/hydrogen peroxide. The toxicity is further added due to the formation of nitric oxide (NO). Superoxide reacts chemically with NO to form peroxynitrite (ONOO). The inflammatory transcription factor pathway (NFkB) is triggered by ONOO due to activation of IkB kinase (IKK). The cascade of changes results in the intensification of expressions, iNOS activity and chronic inflammation in tissues even by exposing to a very minute dose of smoke [53]
• Help in Smoking Cessation –  Catechins present in green tea is capable of scavenging superoxide oxide, NO, and ONOO [54, 55]. In addition, EGCG has the ability to suppress activation of NF-kB that leads to inhibition of phosphorylation. It can further trigger the collapse of the inhibitory sections IkB-a in human pulp cells. The IkBa is also accountable for overturning nuclear transfer of NF-kB operating subunits (p65 and p50) and stimulation of pro-inflammatory genes [56, 57]. EGCG resulted in decreased NF-kB expression and reduction of proteins facilitated including matrix metalloproteinase9 (MMP-9). The MMP-9 is implicated in the breakdown of extracellular matrix, nterleukin-8 (IL-8) and iNOS present in bronchial epithelium [58]. There are more than 4700 oxygen/nitrogen species and reactive chemical compounds in the cigarette smoke. Nicotine is the main chemical compound released from cigarettes that affects gingival and periodontal health [59]. Nicotine stimulates apoptosis across ROS generations of human gingival fibroblasts (HuGF) [60]. The metabolites of nicotine such as tobacco-specific nitrosamines (TSNAs) are considered major carcinogens.
• Anti-allergenic agents – Leukaemia cells are sustained in part by secreting a small protein molecule called vascular endothelial growth factor (VEGF). This binds to protein receptors embedded in the membrane of the leukemia cells and can promote the resistance to cell death typical of this type of cancer.[
• Green Tea Can Improve Brain Function and Make You Smarter – Green tea does more than just keep you awake, it can also make you smarter. The key active ingredient is caffeine, which is a known stimulant. It doesn’t contain as much as coffee, but enough to produce a response without causing the “jittery” effects associated with too much caffeine. What caffeine does in the brain is to block an inhibitory neurotransmitter called Adenosine. This way, it actually increases the firing of neurons and the concentration of neurotransmitters like dopamine and norepinephrine [61, 62]. Caffeine has been intensively studied before and consistently leads to improvements in various aspects of brain function, including improved mood, vigilance, reaction time and memory [63]. However, green tea contains more than just caffeine. It also has the amino acid L-theanine, which is able to cross the blood-brain barrier [64]. L-theanine increases the activity of the inhibitory neurotransmitter GABA, which has anti-anxiety effects. It also increases dopamine and the production of alpha waves in the brain [65]. Studies show that caffeine and L-theanine can have synergistic effects. The combination of the two is particularly potent at improving brain function [66, 67].
• Fat Burning and Improves Physical Performance – If you look at the ingredients list for any fat burning supplement, chances are that green tea will be on there. This is because green tea has been shown to increase fat burning and boost the metabolic rate, in human controlled trials [68, 69].In one study in 10 healthy men, green tea increased energy expenditure by 4% [70]. Another study showed that fat oxidation was increased by 17%, indicating that green tea may selectively increase the burning of fat ([71]. However, some studies on green tea don’t show any increase in metabolism, so the effects may depend on the individual [72]. Caffeine itself has also been shown to improve physical performance by mobilizing fatty acids from the fat tissues and making them available for use as energy [73, 74]. In two separate review studies, caffeine has been shown to increase physical performance by 11-12%, on average [ 75].
• Effect on Obesity – The effects of tea on obesity and diabetes have received increasing attention. Tea catechins, especially EGCG, appear to have antiobesity and antidiabetic effects [76]. African black tea extract has been shown to suppress the elevation of blood glucose during food intake and reduce the body weight in KK-A(y)/TaJcl diabetic mice [77]. Although few epidemiological and clinical studies have shown the health benefits of EGCG on obesity and diabetes, the mechanisms of its actions are emerging based on various laboratory data. These mechanisms may be related to certain pathways, such as through the modulations of energy balance, endocrine systems, food intake, lipid and carbohydrate metabolism, and redox status [78].
• Anti-atherosclerotic Effects – In the book “Yojokun” published in the Edo period, Ekiken Kaibara described that according to the ancient Chinese medical doctor, long-term drinking of green tea would result in a lean body by removing body fat. Evidence has accumulated to show that the ingestion of green tea and tea catechins leads to a reduction in body fat as described in recent reviews.^[79] The stimulation of hepatic lipid metabolism might be a factor responsible for the anti-obesity effects of tea catechins. Tea catechins are suggested to inhibit cell growth by suppressing lipogenesis in human MCF-7 breast cancer cells through down-regulation of fatty acid synthase gene expression in the nucleus and stimulation of cell energy expenditure in the mitochondria.[^80]The experimental data indicated that the suppression of fatty acid synthase gene expression by tea polyphenols may lead to down-regulation of signal transduction.