Green Tea and Its Numerous Health Benefits

Abstract

Green tea is one of the most popular antioxidant drinks in the world. To make green tea, you must first remove the leaves from Camellia sinensis. A form of tea made from unoxidized green leaves from a tea plantation is called green tea. Several other studies have been undertaken over the past year to evaluate whether consuming green tea and extracts has any health benefits. In order to get the health benefits of green tea, the nutrients in the tea must be absorbed. Green tea’s flavonoids and caffeine, which serve to accelerate the elimination of metabolites, contribute to the antioxidant function of green tea. Cancer, heart disease, and aging appear to be the main diseases to be reduced or prevented by these antioxidants. The pharmaceutical and culinary industries can use green tea due to its high potency and lack of adverse effects. Green tea is touted as a natural remedy for a wide range of health issues. Through this, we can better understand the immediate benefits of green tea. Prescription green tea components are discussed along with their antioxidant, anticancer, and antiviral actions in relation to the treatment of cardiovascular diseases (CVD).

1. Introduction

The Camellia Sinensis plant, from which tea is produced, is cultivated in more than 30 countries throughout the globe [1, 2]. White tea, green tea, black tea, and oolong tea are the four varieties of tea produced [3, 4]. This type of tea is made from the same plant, C. Sinensis, as the previous varieties. White tea undergoes the least processing, followed by green tea, which are both unfermented, oolong tea, which is partially fermented, and black tea, which is fermented, all of which undergo an oxidation process before being consumed [5]. Compare to other teas, green tea is among the least oxidized. Green tea is available in many forms, such as tea bags. Loose-leaf, instant power, and supplement sold in capsule form. It is made from unfermented leaves with minimal processing and contains catechin (80–90%) and flavanols (<10%) [6]. It provides a high concentration of antioxidants called polyphenols. Currently, green tea is mostly consumed in China, Japan, and Korea. It is responsible for improving blood circulation, lowering cholesterol levels, preventing a variety of cardiovascular problems, and protecting against the harmful effects of a high-fat diet [7, 8]. Worldwide, black tea accounts for around 78% of total consumption, and green tea accounts for approximately 20% [9, 10]. Green tea can bring relaxation and a calm feeling to its lovers, unlike soft drinks or liquors.

2. Research methodology

Data for this research was sourced from Pub Med, Science Direct, Google Scholar, the World Wide Web of Science, and Cochrane review. We used a variety of keywords, including “Green Tea,” “Tea AND health Benefits,” “herb,” “herbal Medicines,” and “Green Tea AND Cancer” to search these databases.

3. Results and discussion

3.1 History

The history of tea drinking started in 2737 BC. AD, according to Chinese tradition, when Emperor Shen Nong, a skilled ruler and scientific trained, discovered tea by mistake [11, 12]. Camellia species have spread from Nepal to Taiwan. Japan in East Asia has more than 90 species, tea is the most distributed [13, 14].

Green tea is very popular in East Asia (especially in China and Japan), while black tea is in the West. The use of tea leaves probably began in southwestern China over 3000 years ago. It was initially used only for chewing and drinking, much like using coffee for the first time [15]. The origin of the tea plantation was estimated by Sealy [16] around the Chinese Yunnan district, but it is not confirmed. Wild form of the Assamica variety of C. Sinensis was discovered in India in 1835, then in Thailand and Burma [17, 18].

3.2 Green tea composition

The chemical composition of green tea differs from climatic, seasonal, horticultural, and foliar synthesis [19]. The most important components of green tea are polyphenols. The catechins make up 80–90% of the flavonoids and about 40% of the water solids in green tea [20]. Green tea contains more catechins than other forms of tea. It is mainly due to post-harvest processing. The four main catechins contained in green tea are (−)-epicatechin (EC), (−)-epigallocatechin (ECG), (−)-epicatechin 3-gallate (ECG), and (−)-epigallocatechin gallate (EGCG) [21, 22] (Figure 1). EGCG, having the high concentration, has been widely studied for its health benefits. It contains (~60%), followed by EGC (~20%), ECG (~14%), and EC (~6%) (Figure 2). As mentioned above, the amount of catechins in any specific green tea beverage can vary greatly. At the same time, the standardized extract is available for use in addition [23].

Figure 1.

Different benefits of green tea.

Figure 2.

Different forms of catechins.

3.3 Medicinal value of green tea

3.3.1 Antioxidant properties

Different compounds found in green tea showed significant in vitro and in vivo antioxidant effects. Indeed, ECGC-specific green tea originating from catechin is a potent antioxidant capable of inhibiting the growth of cancer cells [24]. Green tea can boost humoral and cell-mediated immunity and reduce the risk of cancer and cardiovascular diseases. ECGC is responsible for much of the chemopreventive properties of green tea against cancer [25]. It is suggested to induce apoptosis and promote the arrest of cell growth by alternating expression of cellular regulatory proteins [25]. As already mentioned, green tea contains a large amount of antioxidants called polyphenols. There is ample evidence supporting the ability of green tea flavonoids to prevent tumors by suppressing free radical production [26, 27, 28]. These antioxidants can slow or inhibit the development of cancer and heart disease, promote immune function, and delay the aging process (Figure 1) [29, 30, 31, 32].

3.3.2 Cardioprotective diseases protection

Cardiovascular diseases (CVD) are unpredictable problems that include various variables. Associated risk factors include irritation, oxidative pressure, platelet total, and lipid digestion. In recent years, many studies have focused on the possibility of using green tea against CVD [33, 34]. Smoke-related heart disease is associated with several risk factors. They are most common in the western world, likely due to the lifestyle in this part of the world, which involves a diet high in saturated fats and low physical activities [35, 36].

It has been reported that people who drink at least 3 cups of green tea per day have a 2% lower risk of stroke compared to those who drink less than one cup a day [37]. Regular consumption of green tea tends to reduce the risk of high blood pressure.

One of the causes of high blood pressure is the lack of arterial elasticity. Over time, this elasticity is lost and one of the causes of arterial constriction is thromboxane. The source of hypertension is an enzyme called angiotensin-converting enzymes (ACE), which is secreted by the kidney. Green tea has been reported to inhibit the activity of this enzyme, which significantly lowers blood pressure [30, 38].

3.3.3 Anticancer properties

A variety of studies based on people’s dietary habits have confirmed the anti-cancer effect of green tea [39, 40]. For example, the cancer incidence rate tends to be low in countries like Japan, where green tea is regularly consumed. One of the benefits of green tea is that carcinogenesis in the digestive tract is believed to be inhibited by the action of ECGC [41, 42].

Colorectal cancer may be prevented or delayed by adopting a healthy diet and lifestyle. Obesity increases the risk of developing abdominal cancer, especially if the obesity is visceral and results from an unhealthy lifestyle that lasts for a long time [43]. Colorectal cancer may be less likely to occur if EGCG consumption inhibits tumor growth factors. Apoptosis, or programmed cell death, caused by EGCG may also be a way to kill cancer cells. Obesity-related carcinogenesis may be reduced by increasing insulin and leptin tissue sensitivity and decreasing blood lipid levels. Recurrent adenomas, which in the majority of cases can progress to colorectal cancer, may be prevented by taking green tea extract supplements [44]. According to numerous studies, EGCG supplementation can reduce the risk of cancer in the gallbladder and bile ducts [45, 46].

Treatment, as well as prevention against cancer, may involve the use of catechins [47]. The anti-cancer activities of vitamin C have been linked to its antioxidant abilities [48, 49].

3.3.4 Antiviral properties

Patients suffering from infectious disorders, including COVID-19, may benefit from green tea’s immunomodulatory and antiviral characteristics [50, 51]. There are several types of research on the antiviral activities of green tea, but most of them are based on traditional accounts [8, 10, 32, 52, 53]. Despite the fact that green tea has a special composition and ratio of bioactive components, the mechanism of action and distinctive features of green tea remain a mystery. It is still possible that matcha green tea has antiviral properties (by inactivating SARS-CoV-2), as proven by Ohgitani et al. in one of the few trials, but additional research is required [54]. Chemicals found in green tea that have been researched for their putative properties and possible modes of action are listed in Table 1.

Activities	Green tea Active compounds	Mechanisms of Action	References
Cardio-protective properties	EGCG	Inhibited stress-induced protein kinase activation and other inflammation-inducing signaling pathways	[55, 56]
	Rutin	Induced vascular support	[57]
Anticancer properties	Catechins	Inhibited tumor growth factors; Induced cancer cell apoptosis	[44, 47]
	Vitamin C	Prevented and treated cancer	[48, 49]
	Phenolic acids	Inhibited cancer cell development; Avoided metastases	[52]
	EGCG	Induced antioxidant effects; Reduced inflammatory mechanisms causing hyperproliferation and onset of carcinogenesis; Increased insulin and leptin sensitivity; Decreased lipid levels	[44, 45, 47, 53]
Antiviral properties	Catechins	Inhibited SARS-Cov-2 primary proteases; Disrupted viral replication cycle; Inhibited HCV replication	[58, 59, 60, 61]
	EGCG	Inhibited SARS-CoV-2 main protease and SARS-CoV-2-like protease 3C	[54, 59, 62, 63, 64, 65, 66, 67]
	Quercetin	Inhibited SARS-Cov replication by protease inhibitors	[68]
	Catechins and quercetin	Inhibited structural proteins and primary protease of COVID-19	[50]
Anti-inflammatory properties	EGCG	Reduced inflammation by neutralizing oxidative stress	[69, 70]
Cognitive enhancement properties; Preventive properties against neurodegenerative diseases	Caffeine	Inhibited the aging process of the brain by reversing oxidative processes, and reducing neuroinflammation reduced cognitive loss likelihood	[71, 72, 73, 74]
	EGCG	Inhibited ROS formation; Increased insulin sensitivity; Reduced brain amyloid buildup	[75, 76, 77]

Table 1.

Summary of studies on green tea’s health benefits.

3.4 Anti-inflammatory properties

Many disorders are accompanied by an inflammatory response. Chemicals that encourage the production of reactive oxygen species (ROS), which may cause cell damage and long-term dysfunction throughout the body, can induce inflammation and cell damage. Anti-inflammatory and antioxidant compounds have the primary function of scavenging ROS and inhibiting inflammatory signaling [78].

EGCG, the main bioactive component of green tea, may reduce inflammation-related side effects, such as lung damage and dysfunction, after major heart surgery, including cardiopulmonary bypass [79, 80]. Gallstone development is less likely when the inflammatory state is controlled by this molecule. Several genes regulate high blood pressure, and inflammation and vascular remodeling are thought to play a role in its development [70, 81]. The consumption of green tea drinks containing high levels of bioactive components that regulate inflammatory processes has been shown to reduce the risk of developing hepatitis.

3.4.1 Cognitive enhancement and neurodegenerative disease prevention

Drinking green tea has been shown to improve mental clarity and cognitive functioning. EGCG is the key ingredient for these health benefits [76]. Age-related cognitive declines can be influenced by several variables, including lifestyle [82]. Caffeine consumption, especially in older women, appears to have a protective effect against cognitive deterioration [73]. Caffeine’s ability to reverse oxidative processes and reduce neuroinflammation may help keep the brain healthy as we age [74]. Memory loss may be caused by oxidative stress, which may cause neuronal damage. As a potent anti-inflammatory agent, caffeine administration may help to keep this condition at bay [71]. Caffeine’s protective effects on the nervous system and its ability to delay the onset of neurodegenerative illnesses are directly related to its ability to reduce amyloid- deposits in the brain [72]. Lipopolysaccharide (LPS)-induced systemic inflammation plays an important role in neurodegenerative disorders. EGCG inhibits LPS-induced reactive nitrogen species (RNS) production, showing that it is a potent and effective neuroprotective treatment for neurological diseases caused by inflammation [77]. Consumption of EGCG improves cognitive performance, insulin sensitivity, and brain amyloid- formation; reduces neuroinflammation; and prevents neuropathologies associated with neurodegenerative disorders, such as Alzheimer’s disease.

4. Future prospects

Green tea has a unique blend of health benefits due to its bioactive components shown in Table 1. As a result, green tea has higher concentrations of phenolic acids, quercetin, rutin, theanine, and chlorophyll than other varieties. It is an entirely new product that cannot be compared to any other green tea on the market today. The administration of its infusions and extracts may be effective in the prevention of free radicals and inflammatory disorders, as well as premature aging. The convenience of powdered green tea makes it an excellent meal supplement. Green tea’s health benefits have not been properly studied. Several elements of its function, including its interactions with the gut microbiota and its impact on infectious diseases, warrant further study in this area. More research will be needed to prove the health benefits of green tea, including further examination of green tea’s chemical composition, and further in vitro and in vivo studies. Additional randomized clinical trials (RCT) research is also required. Moreover, pharmacodynamic and pharmacokinetic aspects of identified compounds should be investigated to validate their actions and well as their bioavailability. On the other hand, toxicological investigations of green tea main compounds should be carried out with different doses and several periods to validate their safety.

5. Conclusion

Green tea antioxidants are attracting increasing attention due to their potential for application in preventive medicine and in the food industry, as well as their pharmacological effectiveness and lack of adverse effects. Growing awareness of antioxidant phytoconstituents and their use in diet and daily use may provide the human body with potential support to combat these diseases. Green tea is becoming a natural remedy for a wide range of health issues. With the latest technological advancements, the different abilities of green tea have been explored. Recent use of green tea in nanotechnology has indicated promising evidence for its bioavailability using lipid nanocapsules and liposome encapsulation to deliver EGCG. These results are encouraging. Many of these properties of green tea have been discovered through numerous preclinical studies, and there is still a lack of human clinical evidence for them. Thus for green tea to be used as a safe and effective medicine, there is an urgent need to test the efficacy, health, and translation guidelines.

Abbreviations

ACE	Angiotensin-Converting Enzymes
CVD	Cardiovascular Diseases
EC	(−)-Epicatechin
ECG	(−)-Epicatechin 3-Gallate
EGC	Epigallocatechin
EGCG	(−)-Epigallocatechin Gallate
LPS	Lipopolysaccharide
RNS	Reactive Nitrogen Species
ROS	Reactive Oxygen Species