Green tea is one of the most popular beverages in the world, especially in Asian countries. Since ancient times, green tea has been considered a health-promoting beverage. Recent research has led scientists look into specific compounds in green tea which are beneficial to health.
Green tea contains an antioxidant substances known as catechins, a family of polyphenols found in plants. A particular catechin called epigallocatechin-3-gallate (EGCG) is known for anti-inflammatory effects because it is the most abundant and most active in the body. EGCG is also being investigated in the light of cardiovascular disease, the rise of obesity and type 2 diabetes mellitus. EGCG is mainly absorbed in the intestine; bacteria comprising our gut microbiota play a critical role in its metabolism prior to absorption [i]. For this reason, some people absorb EGCG better than others via the digestive tract [ii].
Certain studies have highlighted pronounced cardiovascular and metabolic health benefits (anti-diabetic and anti-obesity actions) can be obtained by regular consumption of 5-6 or more cups of green tea per day. Other intervention studies, using similar amounts of green tea containing 200-300 mg of EGCG extract, have also shown benefits for maintaining cardiovascular and metabolic health [iii].
EGCG is also found in other teas such as white, oolong, and black teas. It is also found in berries and nuts such as cranberries, strawberries, blackberries, kiwis, cherries, pecans, pistachios, and hazelnuts in smaller amounts [iv].
Green tea also contains other health-promoting catechin polyphenols such as: epigallocatechin (EGC) and epicatechin (EC). These compounds, along with EGCG, are being investigated for their anti-cancer, anti-microbial, antioxidant and neuro-protective (nervous system protective) benefits [v].
The proposed anti-cancer effect of green tea is said to be the most attractive point in terms of current research. Understanding EGCG is important to explore it as a potential cancer-protective and chemotherapeutic agent [vi].
EGCG may be involved in the prevention of crucial steps of cancer growth proliferation, survival, and the spread of cancer to other parts of the body. It is proposed that EGCG should be considered for new combined treatments in which EGCG acts synergistically with cancer drugs [vii].
Green tea and EGCG has been studied in great detail in breast cancer. In test-tube studies, EGCG shows antioxidant properties. Animal studies suggest EGCG administration results in the reduction of tumour growth and prevention of cancer spreading around the body. EGCG may also present anti-angiogenic effects. Angiogenesis is the process whereby tumours create new blood vessels to direct blood and nutrients towards themselves in order to survive and thrive in the body. Writers of a review concluded that there are implications of EGCG for breast cancer prevention and therapy [viii].
Antiviral activities of EGCG with different modes of action have been demonstrated on diverse families of viruses, including important human pathogens like human immunodeficiency virus (HIV), influenza A virus and the hepatitis C virus. Additionally, the EGCG molecule interferes with the replication cycle of DNA viruses.
In terms of antibacterial action, EGCG alone and in combination with different antibiotics have been analysed against a number of bacteria including drug-resistant strains.
Furthermore, the catechin EGCG has anti-fungal activity against yeasts like Candida albicans, which cause disease when populations overgrow in humans [ix].
Heart and Cardiovascular Health and Diabetes:
Green tea has shown numerous cardiovascular (heart and circulatory) health promoting benefits through various pathways. EGCG was found to exhibit a wide range of therapeutic properties including helping to prevent the accumulation of plaques in the arteries (known as atherosclerosis) and protection against heart attacks.
These therapeutic effects are mainly associated with the inhibition of low-density lipoprotein (LDL) cholesterol, commonly known as the “bad cholesterol”. EGCG in green tea was also found to inhibit NF-κB, part of the pathway for generating chronic inflammation in the body linked to heart disease. Reduction in plasma glucose and glycated haemoglobin levels was also seen in response to EGCG administration, meaning it was seen to have anti-diabetic actions. Additionally, the antioxidant action of EGCG and other green tea catechins were seen to inhibit reactive oxygen species which cause oxidative damage to tissues in the body, which leads to chronic disease such as cardiovascular disease [x].
Nervous System and Brain Health:
EGCG and green tea have been seen to improve neurological (nerve) cell function and preventing degenerative brain diseases such as dementia. Such benefits can be attributed to the protective antioxidant propensity of catechins such as EGCG and their potential to prevent or slow plaque in the brain, which causes Alzheimer’s. A higher intake of green tea was associated with a reduced risk of age-related brain decline, including Alzheimer’s as well as Parkinson’s disease [xi].
Immunity and Autoimmunity:
Recent research has proposed EGCG as an effective compound by which to counteract hyper-inflammation caused by an over-reactive immune response [xii].
Applications of EGCG for autoimmune conditions have also been discussed, including conditions such as multiple sclerosis. The proposed protective effect of EGCG is associated with the suppressed proliferation of cells linked to autoimmunity, including auto-reactive T cells. ECGC is also related to reduced production of inflammation generating proteins (pro-inflammatory cytokines), and has a balancing effect on certain arms of the immune system including T helper cells [xiii].
EGCG has also been indicated for its potential benefits regarding COVID-19 such as suppressing ACE2 (a cellular receptor for SARS-CoV-2) to the entry of the virus into our cells, thus controlling infection [xiv]. It is also thought EGCG has other benefits in viral Upper Respiratory Tract Infections infections such as antiviral, anti-sepsis actions, anti-fibrotic (blood clotting) effect as well as controlling inflammation via signalling of many inflammatory mediators [xv].
It is advisable to keep caffeine intake low during pregnancy and lactation. Use in young children is also not advised. Also, certain heart conditions can be exacerbated by caffeine intake and so use is not advisable.
Stimulant drugs such as Ephedrine.
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