Green tea comes from the tea plant Camellia Sinensis. The same plant is used to make other types of teas e.g. black, yellow, oolong, white and dark tea.
The health benefits of Green tea have been the focus of study for the past 30 years (1,2).
The health benefits of Green tea are attributed to the bioactive compounds called Green Tea Polyphenols which constitute about 30% of the total dry weight (3,4).
Most abundant green tea polyphenols (GTPs) are Flavanols (Catechins).
Green tea extract in powder or liquid form has variable quantities of polyphenols (45-90%) and caffeine content (0.4-10%) (5).
(-)-epigallocatechin-3-gallate (EGCG) is the most abundant of 4 Catechins in Green tea. Other 3 include epicatechin, epigallocatechin, and epicatechin-3-gallate (6).
EGCG has been studied in many studies for the health benefits of Green tea.
1) Green Tea Promotes Weight Loss
Research on catechins and caffeine has demonstrated that the mixture of two could promote weight loss by fat oxidation (fat molecule breakdown), increasing energy expenditure while keeping the body muscle mass (7).
Combining green tea extract with a low-energy diet (LED)can also improve weight loss. (8).
EGCG in green tea increases lipolysis ( fat burning) and has anti-adipogenic (inhibition of fat cell formation) properties. These effects on fat cells promote weight loss (9).
The effects of consumption of green tea extract (50 mg caffeine and 90 mg EGCG) were measured in healthy men.
The 24-hour energy expenditure and fat metabolism were increased compared to caffeine only consumption (10).
Other studies have shown similar effects of catechins in promoting energy expenditure and fat oxidation (11,12).
Green tea is a mild appetite suppressant, therefore, it can help in lowering the daily energy intake (13).
Green tea can also help in the weight maintenance phase of weight loss.
The high habitual caffeine consumption with green tea extract capsules promoted more weight loss compared to low habitual caffeine consumption.
But during the maintenance phase taking low habitual caffeine with green tea extract capsules was more effective than high caffeine with green tea extract capsules (14, 15).
A study in men with similar BMI and waist circumference showed a weight and waist circumference decreased after 12 weeks of tea containing Catechins.
Moreover, the LDL was significantly reduced after Catechin containing tea consumption (16)
Green tea can aid in weight loss due to its interaction with lipids and its thermogenic properties.
2) Green Tea is Helpful in Diabetes Management
Animal studies show that Green Tea Polyphenols (GTPs) and EGCG increase glucose tolerance and reduce blood glucose levels and insulin levels (17,18,19).
Green tea preparations can also have glucose-lowering effects in humans (20).
In humans, a retrospective cohort study on more than seventeen thousand individuals in Japan showed lower diabetes type 2 risk. The effects were more visible in women and overweight men (21).
Another observation of people in the Mediterranean region over a period of two years showed the lowered prevalence of diabetes in those who consumed green tea or black tea (22).
These studies show that green tea consumption and supplementation of EGCG could provide a way to lower the blood glucose and the risk of diabetes type 2.
Robust human studies are required to establish the mechanism of EGCG activity in lowering blood glucose.
Green tea and its extract can have blood glucose-lowering and possible dietary intervention role in diabetes type 2.
3) Green Tea Has Antioxidant Properties That Helps reduce Disease Risk
Antioxidants compounds have an important role to protect cells against the destructive effects of free radicals and reactive oxygen species (ROS) such as singlet oxygen, superoxide, peroxyl radicals, and hydroxyl radicals.
ROS can cause oxidative stress and cell damage (23).
Green Tea Polyphenols (GTP) interact with ROS and have free radical scavenging properties towards oxygen-free radicals and nitrogen species and inhibit their destructive functions (24,25).
Animal research shows that green tea extract has a complementary effect along with vitamin C to reduce the effects of ROS (26,27,28).
In humans, a study shows significant antioxidant effects after the consumption of tableted green tea extract in patients with gastrointestinal pathologies (29).
The study showed a better quality of life and decreased antioxidant profile.
The green tea and green tea extract have beneficial antioxidant properties.
4) Green Tea Kills Microbes including Bacteria and Fungi
Catechins in Green Tea are responsible for killing bacteria such as Staphylococcus epidermidis, Staphylococcus aureus, and Vibrio cholerae O1 by destroying their cell membrane (30).
Green tea can also aid in the fight against bacteria that causes dental caries e.g. Escherichia coli, Streptococcus salivarius, and Streptococcus mutans (31).
Green tea extract has the ability to inhibit toxins.
More specifically, it can inhibit the ability of bacteria to release toxins thus, essentially preventing bacteria from imparting potential harmful properties (32,33,34).
A recent study shows that green tea EGCG inhibited the Zika virus into cells and could provide therapeutic potential in a drug form (35).
EGCG has been shown to inhibit the HIV virus in a recent study (36).
Green Tea bioactive agents polyphenols promote immune cells i.e. Natural Killer cells in the body to induce antiviral activity (37).
EGCG can directly kill bacteria and viruses, including the influenza virus. Thus, taking tea can be useful for flu and influenza (38).
The antimicrobial activity of Green tea is useful against a wide variety of infections. It also has a role in enhancing immune system function.
5) Green Tea Has Tumor Suppressing Properties
Studies on tumor cells have shown that EGCG causes cell cycle arrest and cell death (39,40,41).
The EGCG from Green tea is also shown to inhibit VEGFs (Vascular Endothelial Growth Factors) that are required for tumor spread to secondary sites through a process called angiogenesis (42).
Animal studies have shown that Green tea extract applications on the skin had an anti-tumor effect against melanoma (skin cancer) (43,44,45).
In humans, skin applications can help prevent the harmful effect of UV rays and reduce the risk of skin cancer (46).
Green tea Catechins have shown to suppress tumor invasion and metastasis by inhibiting the promoter of metastasis called Matrix metalloproteinases (MMPs) (47).
Research on human cells has shown that Green tea bioactive compounds can protect against gastrointestinal cancers (48,49,50).
Several animals and human cell studies have shown that Green tea has anti-tumor potential in different types of cancers such as lung cancer, leukemia, breast cancer, prostate cancer cells (51,52,53,54,55,56,57).
Green tea extract containing EGCG and catechins have antitumor effects. Many of the studies in human cells have shown a protective function against tumors. Thus, Green tea could be a good addition to a daily diet.
6) Green Tea Can Reduce the Risk of Heart Disease
Animal studies confirmed that Green tea has a heart protection function by improving lipids (fat molecules) breakdown, reducing the inflammation, antioxidant activity and promoting activities that protect heat from cardiovascular conditions (58,59,60).
Also, Green tea has cholesterol and blood pressure-lowering function in animals (61,62).
In human cells, non-fermented Chinese Green tea is shown to have anti coronary heart disease function (63).
A large meta-analysis of human studies observed that individuals who did not consume Green tea had a greater risk of cardiovascular disease.
Including 1 cup/day of Green tea had reduced the risk of heart attack and stroke compared to those who consume less than a cup of Green tea/ day (64).
Green tea has a heart-protective function by various biochemical pathways in animals and humans.
7. Green Tea Has the Potential to Protect the Stomach & Intestines
The risk of gastrointestinal diseases can be reduced by Green tea extract consumption (65,66).
Furthermore, research has described the Green tea benefit in protection against gastric mucosal lesion in rats (67,68).
Green tea liquid consumption is also associated with improving microbiota in the human gut.
Consuming green tea promotes those bacterial types that reduce inflammation (69).
In humans, green tea consumption can promote healthy bacteria that promote anti-inflammation in the human gut. More studies will explain the mechanism by which Green tea helps protect the stomach and intestines.
8) Green Tea is Good for Brain Health
Green tea has neuroprotective benefits. The caffeine in Green tea can help you stay focused.
Animal studies with Green tea extract show protection against brain injury and reduced cell death (70).
Green tea polyphenols have this protective function by antioxidant and free radical scavenging activity (71).
The neuroprotective activity is also extended to neurodegenerative diseases like Parkinson’s and Alzheimer’s (72,73,74).
Animal studies have also shown that regression in brain function can be slowed down with Green tea extract usage (75).
Green tea contains Theanine that could improve memory and promote learning and mood neurotransmitters e.g dopamine and serotonin in rats (76).
In human Theanine is observed to have a relaxation effect because it is readily absorbed and transported to the brain (77).
Green tea bioactive agents may have a protective function against dementia (78).
Green Tea extract and bioactive agents have a neuroprotective function from injury, Alzheimer’s and Parkinson’s disease, enhance memory, learning and induce relaxation.
9) Green tea has Pain-relieving and Anti-Inflammatory properties
The anti-inflammatory action of Green tea has been studied in animals (79).
Green tea is an inhibitor of chronic inflammation by suppressing angiogenesis (80).
Green tea also induced suppression of anti-inflammatory activity in the skin tumor mouse model (81).
Green tea leaves have anti-allergic activity due to saponin bioactive compounds in small animals (82,83).
Green tea tablets have shown to be effective in controlling pain in patients suffering from osteoarthritis (84).
Green tea extract has an anti-inflammatory function and pain-relieving function.
10. Green Tea is Good For Teeth, Bones, and Muscles
Japanese Green tea extract was useful in killing root canal in humans, thus the antibacterial function of Green tea can be useful for maintaining oral health (85).
Dental caries and bacterial infections could be prevented with Green Tea extract due to fluorides and a bioactive compound called Pectin (86,87).
Green tea could also prevent periodontal diseases (88).
Thus, Green tea has a teeth-protective function.
In animals, EGCG of Green tea is able to dilate blood vessels in the muscles and thus increase blood flow to muscle cells (89).
It could also induce muscle regeneration and also recovered muscle mass and function (90,91).
EGCG also has an anti-inflammatory function for the treatment of the collagen membrane which can be used in bone regeneration (92).
EGCG could also suppress the development of arthritis in human cells (93).
A trial human on osteoarthritis showed that Green tea extract was able to reduce the pain and improve knee joint function (94).
Green tea can help in improved body function due to its contribution to muscle and bone regeneration function. It may also help slow down arthritis and pain.
Take Away
Green tea can be a beneficial addition to your dietary regimen. Many of the studies have been done in animals and there are other epidemiological and human cell studies in humans that have shown beneficial effects of green tea bioactive compounds.
Since the ingestible quantity of Green tea is very low and large dosage can be harmful, Green tea alone may not provide all or single benefits mentioned above but it could help in an overall strategy to achieve better health with other factors such as better suited diet, sleep, and exercise.
Frequently Asked Questions(FAQs)
Excess to everything is bad. Generally, green tea has beneficial effects yet high consumption can have negative health consequences.
Research has shown that high quantities of EGCG can be harmful to the liver (95).
Consult your physician before taking any high amount of Green tea whether in powdered, extracts, capsules or pill form.
According to the European Food Safety Authority (96), Following individuals should consider consuming Green tea after consulting with their physician:
Pregnant women and breast-feeding women
If you have a liver condition
Anemics because green tea could reduce the bioavailability of iron due to decent amounts of tannins present in it (97).
Patients with kidney issues as Green Tea contains aluminum and may cause accumulation of metals (98).
Green has a tone of health benefits such as weight loss, diabetes management, cardiovascular risk reduction, etc. but in higher doses, it can be harmful as well. It is rare to take large doses of green tea, therefore it is mostly good than bad.
So far, there is no direct evidence of targeted belly fat reduction by green tea. Green tea’s Catechins (including EGCG) are shown to impact weight loss. Adding green tea to your overall weight loss strategy can help a great deal in losing weight. Belly fat will be reduced once the overall body weight is reduced.
In an average Green tea beverage of 250mL, there are 50–100 mg of catechins and 30–40 mg caffeine (99). A daily consumption of 90-300 EGCG is considered safe. In many European countries supplements with 300mg EGCG is considered a limit (100)
