Chemical composition of Green tea
Role of green tea in preventing and fighting cancer
Does green tea help weight loss?
Green tea, what’s in the name?
Camellia sinensis (L.) Kuntze is a flowering plant belonging to the Theaceae Family of the Ericales Order. This species is native to Asia, specifically mainland China, South- and Southeast Asia.
Due its popularity, the tea bush is also cultivated in over 45 countries globally. Different organs of C. sinensis are used to make different types of teas.
Chinese tea is made from leaves and leaf buds. Whereas, twig tea (Kukicha) is produced from the twigs and stems of C. sinensis.
Teas are classified based on the extent of fermentation. Green tea and white tea are unfermented tea, Oolong tea is semi-fermented while black tea and pu’erh tea are fully fermented teas.
Levels of fermentation affects the quantity of compounds found in each tea.
Unfermented tea contains more catechins than either black or oolong tea. In contrast, semi- and fully fermented tea predominantly contain theaflavins, thearubigins and caffeine.
Catechins, caffeine and theaflavins have been found to contain a wide range of activities that promote general health and a range of biological functions.
Chemical composition of Green teaCatechins
Green tea contains approximately 4000 bioactive compounds. It is a very good source of flavanoids.
Flavanoids are a large group of low molecular weight compounds that are defined and grouped based on the variation in arrangement of the same basic structure.
One important group of flavonoids found in green tea is a class of compounds called flavan-3-ols, also known as catechins.
Catechins are in vitro and in vivo strong antioxidants. Catechins are especially concentrated in green tea, accounting for 30 to 40% dry weight.
These antioxidants are thought to aid in the protection of cells from damage. (-)-Epigallocatechin gallate (EGCG) is a major component in green tea that, in addition to being the most abundant, is also the most active.
EGCG has been reported to be the most effective chemopreventive agent found in green tea.
EGCG is especially important and active in many essential cellular pathways including the cell cycle.
The cell cycle is an important cycle responsible for growth, replenishing of damaged cell and general cell division.
It is very important and is tightly regulated, accidental runaway cell growth/division leads to cancer, commonly defined as aberrant cell growth.
EGCG interacts with important cell cycle regulatory proteins, such as cyclins D1 and E and their cyclin-dependent kinases 2,4 and 6.
It also interacts with growth factors including a cytokine called tumor necrosis factor-α (TNF-α) by inhibiting its activity.
This cytokine is a key component necessary for tumor development, therefore its inhibition is important in regulation of tumor progression.
Damaged cells get earmarked for degradation so that they do not accidentally multiplied through cell division.
The process of systemically destroying damaged cell is called apoptosis and is signaled for and controlled by apoptotic proteins. EGCG has also been shown to interact with apoptotic proteins such as Caspase 3, 7 and 8.
Interestingly, it also interacts with antiapoptotic proteins such as Survivin and cFLIP, which regulate the activity of apoptosis protein.
Just like you would not want to propagate damaged cells, you also would not want to uncontrollably destroy healthy cells, this is one of the ways autoimmune diseases can result.
Numerous other beneficial catechins are found in green tea, albeit in comparably lower abundance.
These include, (-)-epicatechin, (EC); (-)-epicatechin-3-gallate, (ECG); (-)-epigallocatechin, (EGC) and (+)-gallocatechin, (GC).
Together with oolong and black tea, green tea is also an excellent source of vitamin C.
Using animal models, in vivo and in vitro studies have suggested that green tea polyphenols interact with a number molecular targets that are active in cellular processes involved in a range of diseases such as certain cancer (further discussed in Role of green tea in preventing and fighting cancer).Essential amino acids and other beneficial compounds
Green tea contains a majority of the 20 essential amino acids including arginine, glutamic acid, glycine, serine, tyrosine and tryptophan.
Amino acids such as aspartic acid, glutamine, glutamic acid and theanine occur in higher levels in green tea than in white tea. Important vitamins, especially vitamin C, are also present in green tea.
Green tea also contains small amounts of minerals that are important for our health such as fluorine, copper and chromium.
The caffeine content of green tea is 15 to 25 mg per 150mL.
Although lower than the amounts found in coffee, the caffeine content of green tea is sufficient to provide that kick we drink coffee for first thing in the morning.
Green tea also contains other compounds like gallic, caffeic, chlorogenic or cinnamic acids.
It is important to note that the nutritional value, specifically the relative quantity of different bioactive compounds in C. sinensis tea is greatly influenced by different factors from growing conditions to manner of tea preparation.Chemical Interaction and interactive mechanism
Biochemical pathway for green tea extracts interaction with known cancer pathwaysMAP kinases
Map kinases are responsible for directing cellular responses to a wide range of external stimuli such as heat shock, osmotic stress and mitogens. Disruption of their function can lead to cells over- or underreacting to certain stressors and triggering reactions such as apoptosis at inappropriate levels.
Map kinases such as p38 and JNK have been implicated in responses to stress that can induce reactions including gene expression and apoptosis.
Chen and authors (2003) sought out to investigate the role of EGCG in fighting human colon cancer.
They treated human colorectal carcinoma cells called HT-29 cells. Cues such as responses in caspase assay, cytochrome c release and MAPK phosphorylation, among others were investigated.
Caspase is an apoptotic protein therefore its activity can be used to study the process of apoptosis.
Cancer cells do not undergo programmed cell death like noncancerous but damaged cells do. In addition, cancer cells go through aberrant cell growth unlike noncancer cells which go through a tightly regulated cell cycle. Cytochrome c is released during the apoptosis process, therefore measuring its release is a good indication that apoptosis is underway. In addition, the authors recorded activation of MAPKs driven by EGCG.
The overall outcomes of this study provided support that EGCG induced apoptotic cell death in cancer cells.
In Japan, other researchers sought to investigate the activity of EGCG in epithelial cells versus normal cells.
They showed that in normal human primary epidermal keratinocytes (NHEK) EGCG induces p57 through the p38 MAPK signaling pathway.
In this context, EGCG aids in the signaling of apoptosis in tumor cells that would otherwise have lost the function of signaling programmed cell death.Green tea comes in many forms
In addition to being enjoyed in a teabag green tea also comes in powdered form. Matcha is powdered green tea important in the Japanese tea ceremony.
It has been posed that this form of green is superior to other green teas in its nutritional benefits.
Authors Weiss and Anderton, used a rapid detection method to analyse select catechins and caffeine to test this belief. Using a mg(catechin)/g(dry leaf) ratio, they found that EGCG concentrations were in deed much greater in drinking matcha, 137 times greater than the amounts found in China Green Tips green tea.
These findings were, by comparison, at least three times greater than the largest value previously reported in literature for other green teas.
Role of green tea in preventing and fighting cancer
Many studies have studied the role of drinking green tea in many ailments ranging from stress, many cancers to diabetes.
In this section we summarize scientific evidence of benefits of green tea, green tea compounds and green tea-derived supplements to our health.
Many studies have attributed almost a third of all cancers to dietary-related causes, therefore the importance of the right type of diet is being pursued as an avenue for reducing certain cancer incidents.
Consumption of green tea has been linked with reduced risk of several cancers such aa lung, esophagus, and stomach cancer.
Due to the diverse array of beneficial compounds, green tea has been shown to possess antitumor, apoptosis-associated, antioxidants and antiproliferative activities. Many of the benefits of green tea are attributed to the EGCG catechin.
Other tea and tea polyphenols have been shown to play an important role in inhibiting, initiating and promoting cellular activities associated with regulating cancerous cells.
In in vitro studies, tea polyphenols (especially EGCG) have been demonstrated to inhibit growth and help in apoptosis in a number of human tumors such as lung, breast, leukemia and melanoma.BREAST CANCER
A Japanese study investigated 472 breast cancer patients for possible association between green tea consumption and possibility of recurrence.
Of the 472 breast cancer patients 390 stage I and II patients were selected based on the filtering process for association between green tea consumption and a variety of phenotypes of breast cancer.
This subset was further investigated during follow-up visits. Increased green tea consumption was significantly correlated with a decrease in recurrence of stage I and II breast cancer.
The authors found that consuming 5 or more cups a day was linked with a lower recurrence rate (16.7%) compared to the recurrence rate (24.3%) in patients that consume 4 or less cups a day.
The benefits peaked at 5 to 7 cups per day. These correlations were thought be due to the modifying effect of the clinically beneficial compounds found in green tea.
A number of studies published between 2001 and 2007 found that EGCG inhibited cell proliferation in cancer cells, but consistently had no effect on normal mammary epithelial cells. They demonstrated that:
EGCG and related polyphenols induce programmed cell death in breast cancer cells through the activation of caspase (apoptosis protein) and mitochondrial (cell’s powerhouse) damage.
EGCG inhibits cyclin D, cyclin E, CDK4, CDK1 and PCN expression, thus directly contributing to the cell cycle regulation.
Dosage and time of EGCG administration affect the rate of apoptosis and activity of caspase-3 induced by EGCG was time and dose dependent.
Nude mice injected with human breast cancer cells were treated with GTP (energy source) and EGCG, these cells showed delayed tumor incidences and reduced tumor burden when compared to control mice control. This study shows supporting evidence that treatment with GTP and EGCG treatment does inhibit proliferation and induces apoptosis of breast cancer cells in vitro and in vivo.
These studies add credence to the hypothesis that GTP together with EGCG possess anti-tumor properties.LIVER CANCER
Authors in China conducted a meta-analysis to better understand the association between consuming green tea and the risk of liver cancer in Japan and China studies.
They found that there was an inverse correlation between tea consumption (>5 cups/day) and liver cancer incidence.
This pattern was increasingly pronounced with increasing years of green tea consumption (significant at more than 20 years of consumption).
So, this would mean to fully appreciate the benefits of consuming green tea you would need to make a > 20-year commitment to 5 or more cups of green tea a day.
To sweeten the pot, if you are a woman that is, the authors also noted a higher protective effect in women compared to men.
Could that second chromosome be coming in handy again? Not the reason this time, this difference was likely attributed to confounding factors related to lifestyle such as cigarette smoking and alcohol consumption.
Much like the study presented above, the line that makes a difference was identified at 4 cups. The dampening of the inverse relationship between green tea consumption and the lung cancer risk factor occurred at 4 or less cups consumed per day.LUNG CANCER
Mice were treated with a potent dose of tobacco, nitrosoamine and then administered a dose of green tea extract containing 2% green tea extract and 1.2 mM EGCC.
These mice did not show any signs of tumorigenesis indicating that these extracts inhibited tumor formation.
Specifically, levels of a marker of oxidative DNA damage, 8-OH-dG, were significantly suppressed in these mice.
Interestingly, a study conducted in women who lived in Shanghai between 1992 and 1994 found an association between lung cancer and drinking tea.
These association was, however, not found in smoking candidates suggesting that cigarette smoking negated the benefits of green tea towards cancer.
These effects were sensitive levels of smoking in the patient with a history of smoking.GASTRIC CANCER
Authors based in the Third Medical University, People’s Republic of China, recently conducted a review focused on the association between green tea consumption and the risk of gastric cancer, looking at the role of dosage.
They found a similar association to that observed by another group looking at liver cancer.
Dosage does play an important role and so does the length of time of green tea intake. In this review, the number of cups per day associated with a significant reduced risk was at least 6 cups per day for 25 years of green tea consumption.
Interestingly, the temperature of tea consumed was found to increase the risk for gastric cancer when the tea is drunk while very hot. T
his observation was however marked as requiring further investigation.OVARIAN CANCER
Canada-based researchers conducted a review on studies focused on the link between green tea and epithelial ovarian cancer cell lines.
In their results they found that green tea and associated extracts are associated with downregulation of the expression of proteins involved in inflammation, cell signaling and angiogenesis.
The associated effects of apoptosis induction were found to be a promising avenue for aiding the effects of a chemotherapeutic cisplatin.
In humans, intake of green tea was associated with a decreased occurrence of ovarian cancer and recurrence in women.
A review out of the University of Bristol published in 2012, was conducted analyzing 8 systematic review and meta-analyses on cancer risk, weight loss and cardiovascular risk.
The authors found that while the evidence connecting green tea and cancer risk was largely inadequate and inconclusive, there is some positive association between risk reduction of some cancers (breast, endometrial and prostate).PROSTATE CANCER
In the US, prostate cancer is recorded as the leading cause of death (in deaths related to cancer) among males.
Much in the studies reported above, green tea and EGCG have been shown to inhibit a number of cancer cell lines, in this case, prostate cancer cell lines.
Of course, the treatment effectiveness was dose-dependent in its inhibition of cell growth, cell cycle arrest, and when appropriate, apoptosis.
These outcomes suggest that green tea extracts can be effective agent in chemotherapeutic agents and, possibly, help block or reverse effects of carcinogenic agents.
A trial focused on the small and large intestines, and prostates of C57BL/6 mice recorded accumulation of black and green tea byproducts tea polyphenols (PP).
Providing a direct link between green and black tea and organs investigated for correlation between green tea active agents and cancers of the intestine and prostate.
Furthermore, in human trials tea polyphenols were found in higher concentrations in green tea consuming men than in those that consumed caffeinated soda (control group).
Interestingly, although tea polyphenols were not detected in serum, prostate cancer cell proliferation was markedly less in cells grown in media supplemented with this serum.
Does green tea help weight loss?
Green tea benefits have been said to include helping with weight loss. However, the big question is, does it work?
And how long can the benefits be sustained for?
Studies have found that green tea can help with weight loss but many of them have only assessed this benefit in a limited timespan.
What does this mean?
Does it mean that green tea is great for supplementing that rushed diet to fit into a dress for that particular special event but not so much for dealing with weight problems long-term?
Levy and co-authors recently showed that over a period of 12 weeks a high dosage of EGCG (875 mg) did result in significant weight loss in women with central obesity. So, that answers our first question about supplementing a short-term weight loss plan.
However, this study looked at women with central obesity, so if one does not fit this category these results may not be experienced.
A previous study by the same authors did not find this significant weight loss in women in this bracket. This emphasizes the importance of dosage.
They had previously only administered a daily dosage 360 mg. In addition to presenting the importance of increased dosage they also presented the importance of physical activity.
For this part, they recruited healthy subjects from Northern Israel and categorized them by level of activity based on the Physical Activity Scale for the Elderly (PASE) Questionnaire.
While this group of researchers provides an effective dosage versus the lower ineffective one, an optimal dosage has yet to be conclusively established.
A study conducted in University of Chichester Research, UK, found that in 13 recreationally active healthy women consuming matcha green tea drinks enhanced fat oxidation during brisk walking.
The measurements focused on time passed since consumption and the length of exercise.
Interestingly, these authors proposed that there might also be synergistic effects between the different components of the drink that lead to increased success of the tea in aiding with fat oxidation.
The authors do caution that the impacts of matcha tea when it pertains to brisk walking should not be overstated when one is participating in a weight loss program.Emotions, mood, attitude and sleep
Green tea has also been praised for its ability to increase cognitive function, physical activation and; in an interesting twist, green tea also also calming, relaxing, stress reducing and sleep promoting effects.
It is still tea and like some other teas, we do enjoy the more Zen properties associated with tea consumption from green tea.
Recently, matcha green tea is gaining appreciation throughout the word as food for the brain and mood.
There have been studies that recognized the positive influence of some tea compounds (also found in green tea) on improved mood and cognitive function.
These compounds included L-theanine, caffeine and the, hopefully by now, very familiar EGCG catechin.
These association were picked in studies looking at these constituents in conjunction and separately.
Dietz and Dekker analyzed 49 human studies to assess whether the compounds in matcha tea were the reason for the properties this tea is hailed for. This review supported has several key findings:
Caffeine was consistently found to be beneficial for alertness and during cognitive tasks performed for an extended amount of time. Findings that some of us can attest to thanks to coffee fueled long hours during school or graduate school examinations periods. In these studies caffeine was also linked with arousal and vigor. Noticeable effects were observable from doses as low as 40 mg.
L-theanine is a component you may have noticed as an ingredient in relaxation and sleep supplements. In studies review it was recorded as self-reported relaxation and calmness inducing, and tension relieving starting at a dosage of 200 mg.
L-theanine and caffeine combined may sound a bit counterintuitive but these two were found to be particularly helpful in attention-switching tasks and alertness but with a dampened impact compared to caffeine alone.
This review could not provide conclusive results on the role of EGCG, this was attributed to limited studies available.
Thus, according to this review, if you are seeking ways to sustain attention and suppressing distraction then L-theanine and caffeine may be the way to go and matcha green tea is a potential source for you.
While studies attempted to provide conclusive proof that green tea is directly linked with interventions on cancer cell reduction/ control gaps exist that hinder the bridging step between integrating green tea into treatments and realizing its full potential.
Green tea has been proven to help in many mild to serious problems ranging from simple restlessness to potentially deadly ailment like cancer.
Hopefully, at this point we have convinced you that while the jury is still out on conclusive links between green tea and the many ailments is seems to be involved in fighting, you should strongly consider drinking green tea (preferably more than 5 cups a day).
If not for the many potential benefits, then for its everyday benefits (which have more solid scientific evidence).
Afterall, we all need that caffeine kick in the morning to help with the transition from sleepy to wide awake, alert and ready to kickstart the day.
Frequently Asked Question
Does green tea affect mood?
Green tea has been praised for its ability to increase cognitive function, physical activation and, in an interesting twist, green tea also has calming, relaxing, stress reducing and sleep promoting effects.
Can I lose weight by drinking green tea?
Yes, green tea is great for helping you fit into that nice dress for a special occasion, but you might want to supplement it with exercise when it comes to maintaining a good figure in the long term.
Does green tea contain caffeine?
The caffeine content of green tea is 15 to 25 mg per 150mL. Although lower than the amounts found in coffee, the caffeine content of green tea is sufficient to provide that kick we get when we drink coffee first thing in the morning.
Can green tea prevent cancer?
Consumption of green tea has been linked with reduced risk of several cancers such as lung, oesophagus, and stomach cancer. Due to the diverse array of beneficial compounds, green tea has been shown to possess antitumor, apoptosis-associated, antioxidants and antiproliferative activities.
Does green tea help fight breast cancer?
Increased green tea consumption is significantly correlated with a decrease in recurrence of stage I and II breast cancer. It was found that consuming 5 or more cups a day was linked with a lower recurrence rate.
Can green tea cause stomach cancer?
Studies have shown that the consumption of 6 cups of green tea per day (for 25 years) was associated with a significant reduced risk of gastric cancer. When the tea was drunk very hot, the temperature of the tea was proved to increase the risk for gastric cancer.
Can green tea help fight lung cancer?
Studies done on mice have shown that certain extracts from green tea inhibit tumour formation. On the downside, it is suggested that smoking cigarettes negates the benefits of green tea towards cancer.
Is green tea bad for cancer patients?
It is suggested that green tea contains an array of beneficial compounds that are related to combating cancer cells. Some tea polyphenols have been shown to play an important role in inhibiting, initiating and promoting cellular activities associated with regulating cancerous cells.
Can green tea reduce the risk of liver cancer?
Studies have discovered an inverse correlation between tea consumption (>5 cups a day) and liver cancer incidence.
Is green tea good or bad for anxiety?
Green tea contains at the same time caffeine and L-theanine. One is meant to keep you alert, the other will relax you. L-theanine and caffeine combined may sound a bit counterintuitive but these two were found to be particularly helpful in attention-switching tasks and alertness but with a dampened impact compared to caffeine alone.
What are some benefits of drinking green tea?
Green tea contains compounds that were found to promote general health and a range of biological functions. Also, it aids in the protection of cells against damage and contains one extremely effective chemopreventive agent.
What is the best green tea?
It depends on the criteria: texture, preparation, health benefits, taste. Matcha green tea has been gaining appreciation throughout the world as food for the brain and mood. It has been posed that this form of green tea is superior to other green teas in its nutritional benefits.
How should you drink green tea?
Green tea should be prepared mindfully to maintain the integrity of all its beneficial compounds. A too high temperature (like that of boiling water) can burn away some of that green tea goodness.
Why is green tea good for us?
Green tea contains small amounts of minerals that are important for our health, such are fluorine, cooper, and chromium. The caffeine content of green tea is sufficient to provide that kick we need first thing in the morning.
What are the effects of drinking green tea?
Green tea has some antithetic effects: on one hand it can induce calm, reduce stress or promote relaxation, on the other, due to its caffeine content, it generates a certain level of alertness.
What's the difference between green, white and black tea?
They are all obtained from a flowering plant called Camellia sinensis. Depending on the extent of fermentation, we can have green and white tea (unfermented), oolong tea (semi-fermented) or black tea (fully fermented).
How much green tea should I drink every day?
Aside from personal preferences, when it comes to consuming green tea as an aid in the fight against cancer, studies have forwarded numbers as high as 5-7 cups a day.