Introduction
Throughout history, tea lovers have touted green tea’s health benefits. So what do current scientists have to say about this drink’s long history? Many articles make outrageous statements about green tea’s miraculous benefits, but the evidence suggests a much different picture.
The extensive health benefits of green tea have been analyzed in countless scientific research papers, some of which are still being studied while others show clear effects. In particular, L-theanine and EGCG have garnered the interest of scientists due to their outlying biological effects. This remarkable drink is backed by clinical studies due to its compelling evidence on heart health and brain function.
This evidence-based guide highlights aspects of green tea that require more research, including its proven and popular misconceptions, along its benefits on one’s health.
The Antioxidant Power of Green Tea Catechins
Epigallocatechin gallate (EGCG) is an antioxidant that constitutes around 50-80% of catechins found in green tea. On a cellular scale, green tea is composed of a unique group of compounds called catechins, which makes it a rich source of antioxidants.
Natural Ways to Maintain a Healthy Heart for Life
What makes EGCG unique among antioxidants
EGCG shows astonishing antioxidant properties. It has been proven to be over 100 times stronger than vitamin C, 25 times stronger than vitamin E and a single cup of brewed green tea has about 200-300 mg of EGCG. [2][1].
The effectiveness of EGCG is attributed to its peculiar molecular makeup. The “chelation” capability of certain metal ions is attributed to the presence of various multi hydroxide groups and certain structural features; specifically, di/tri-hydroxy of B and D rings and meta-5,7-dihydroxy substituent at A ring [3].
How catechins combat cellular damage
Suffice to say, catechins in green tea fight cellular damage through several intricately sophisticated mechanisms:
Direct antioxidant actions:
– Removal of damaging reagents like reactive oxygen species (ROS)
– Chelation of metals like transition metals
– Inhibition of lipid peroxidation peroxides
– Lowering the level of damaged DNA portions 4
Aside from this, catechins also have passive protective actions that stimulate the body’s own antioxidants defenses systems. Under the upper level of 10 µM concentration, EGCG seems to burn some little amount of ROS which seems to turn on some protective actions on the cell [1]. This actions leads to increse of efficiency of major antioxidant enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase [5]. It’s fair to say that the concentration of EGCG defines the role it plays.
Research suggests that low to moderate concentrations (≤ 10 µM) are likely to exhibit antioxidant actions, while covering higher concentrations might show pro-oxidant effects (1). Following this, EGCG in pure form is usually around 10 µM in plasma 5 minutes after consumption.
Contrasting Green Tea with Different Antioxidant Sources
Tea is the second most consumed drink after water, and when the different types of teas are rated on the content of catechins, green tea is the clear winner with more than chocolate, red grapes, wine and apple 4. In a comparison of antioxidant capacity of different types of tea, green tea wins:
• Black tea: 124 mg of total phenols [6]
• Green tea: 165 mg of total phenols(gallic acid equivalents)
In addition, per serving of black tea the quantity of green tea’s antioxidant capacity is 436mg vitamin C, while the amount in black tea is 239mg 6. Green tea composition is mainly catechins while black tea is made of a higher portion of tannins, and this is the primary reason for this difference 4.
These effects of antioxidants on organism have been studied clinically. Research found that green tea consumption leads to an increase of 4% in antioxidant plasma capacity after 40 minutes of drinking 4. What’s more, drinking green tea regularly for 4 cups a day over 4 months could reduce 31% of urinary 8-hydroxydeoxyguanosine concentration, which is an oxidative stress marker in smokers 4. The mechanisms of action for various cellular protective anti-oxidants benefits.
Research indicates that catechins in green tea, especially EGCG, defend against DNA damage by free radicals more than any other polyphenol in nature. These effects, which occur at micromolar levels, are therefore practical when considering the consumption of green tea on a day to day basis [8]. [7] states that regular consumers of green tea have around 30% less bone fractures due to the protective effect micromolar levels provide.
Strong Evidence: Heart and Metabolic Health Benefits
Numerous research conducted demonstrates impressive evidence of the favorable effects of green tea consumption on cardiovascular and metabolic health. As mentioned before, consistent consumption of green tea over long periods of time resulted in drastic improvements across various health parameters in multiple studies.
Impact on cholesterol levels: What studies consistently show
Green tea is well-known for its spectacular effects on cholesterol levels. In 14 meta-analyzed controlled trials, green tea was able to reduce total cholesterol by an average of 7.20 mg/dL [9]. Generally, it is accepted that LDL (bad) cholesterol decreases by 4.55 mg/dL [10]. There is an impressive correlation between intake of green tea and improved cholesterol levels.
A 40,530 participant study completed in Japan found that consuming over 5 cups of green tea resulted in a 26% lower risk of death caused by heart attack or stroke [11]. These benefits are compounded for those with higher baseline cholesterol as participants with total cholesterol exceeding 200 mg/dL experienced the greatest positive changes [12].
Blood pressure reduction mechanisms
There are a plethora of biological reasons as to why green tea is able to lower blood pressure and they all link back to the tea itself.
The catechins present in green tea are known to increase plasma nitric oxide level, which results to better endothelial function and dilation of blood vessels [13]. These compounds deactivate inflammatory signals and modulate calcium waves affecting blood pressure [13].
A meta analysis of randomized control trials revealed that the consumption of green tea decreased:
• Systolic blood pressure by 1.17 mmHg
• Diastolic blood pressure by 1.24 mmHg [13]
The antihypertensive effect is more pronounced in those with high normal blood pressure or with some cardiovascular risks [14]. New evidence suggests that certain green tea compounds stimulate special types of proteins with ion channels (KCNQ5) located in the walls of blood vessels and that these proteins aid in the relaxing of blood vessels [15].
Green tea and insulin sensitivity
Apart from its cardiovascular benefits, green tea look promising effect on glucose level and insulin sensitivity. A meta analysis of 17 trials with 1133 participants showed that the consumption of green tea lowered:
• Fasting glucose level by 0.09 mmol/L
• The Hemoglobin A1c index by 0.30% [16] The factors at work for these improvements are:
1. Better absorption of glucose by the skeletal muscle
2. Higher expression of the glucose transporter IV
3. Enhanced muscular β-oxidation [17] Clinical studies showed that green tea catechin enhances the insulin sensitivity through various mechanisms.
Above all, they enhance glucose metabolism and insulin signaling [18]. In addition, they facilitate the transfer of glucose into skeletal muscle tissue [17].
Research implies that there are certain benefits that come from frequent use. A study assessing the impact of long-term use found that drinking four cups of green tea each day resulted in remarkable improvements in metabolic processes [5]. Nevertheless, there appears to be a dose-response relationship, with higher concentrations of catechins generally leading to stronger effects [10].
Moderate Evidence: Brain Function and Mental Health
Newer scientific evaluation has recently unveiled new and interesting developments concerning green tea and its impact on cognitive function and mental health. Numerous clinical trials illustrate the combined effects of its constituent parts on the functioning of the brain.
The cognitive enhancing duo: L-theanine and caffeine
The combination of L-theanine and caffeine present in green tea is especially powerful benefitting cognitive functions. Evidence suggests that L-theanine crosses the blood-brain barrier utilizing the leucine-preferring transport mechanism [19]. Thereafter, it is able to assist caffeine in enhancing mental performance. Clinical research has showed that this combination contributes to the improvement of:
• Visual reaction time by 26.7 ms [20]
• Accuracy in attention-switching tasks [21]
• Working memory performance [22]
In fact, those taking both compounds exhibited greater cognitive functioning than those using either one alone [23]. The sustained attention and maintenance of memory while ignoring distractions can be done best by the L-theanine-caffeine combination duo [21].
Stress reduction properties
L-theanine shows great potential in reducing stress. Research shows that L-theanine’s 200-400mg daily intake tends to lower the anxiety rate of people in stressful situations [24]. This amino acid does this by:
1. Countering with glutamate receptors to stop neuronal death [19]
2. Leading to relaxation by increasing alpha brain waves [21]
3. Increasing levels of the mood-modulating neurotransmitters [7]
A clinical trial found that people taking matcha green tea showed lower anxiety rates before some difficult tasks [3]. The reduction in stress effect is best with two parameters: when the molar ratio of caffeine to theanine is below two, and when combined with the amino acid arginine [3].
Long-term neuroprotective effects
Apart from direct cognitive advantages, green tea gives considerable protection to the brain in the long term. Its regular consumption is associated with decreased lesions of white matter in the brain, which is a common trait of dementia [25]. This protective effect is most appreciable amongst those consuming 600-1500 ml of green tea in a day [25]. These neuro protective mechanisms are known to engage multiple pathways:
• Increasing levels of glutathione in striatal astrocytes. [26]
• Enhanced neurogenesis via activating CREB signaling. [26]
• Shielding from damage due to oxidative stress. [26]
As an example, one of the most comprehensive studies done on healthy middle-aged Chinese people and elders suggested that green tea drinkers showed significantly better memory and executive function performance than non-drinkers. They also suggest that the protective effects appear more dominant at higher consumption levels, especially with regard to memory and cognitive control systems. [4]
These are the most protective effects I found, but there does seem to be a variation in certain populations. For example, the protective effect from white matter lesions was found to be lower in depressed patients or those positive for the ApoE e4 allele. [25]This is where the researchers say more studies need to be done. [25]
Green Tea and Cancer: Early Studies Start Here
Green tea is positioned as a potential aid in cancer prevention, but research on humans makes things more interesting. Scientists from all over the globe are still looking into these compounds that are known to have promising potential, particularly in stopping tumor growth.
The Gap Between Lab and Human Studies:
A Summary Cell culture and animal studies demonstrate remarkable anti-cancer effects. Green tea extracts, along with it’s polyphenols, suppress tumor development for several types of cancer, which includes skin, lung, oral cavity, esophagus, stomach, colon, liver, pancreas, and mammary glands. [6]. At a molecular level, modulations of crucial cellular pathways include:
- Apoptosis (enhanced conditioned cell death)
- Cell proliferation (suppression)
- Angiogenesis (blood vessel formation) (inhibition) [6].
Still, applying these laboratory discoveries to human advantages is very difficulat. A broad assessment of 142 snapshot studies, consisting of 11 non-experimental and 131 observational trials, have shown contradictory outcomes. Despite some studies indicating protective effects, others depict no benefit at all or possible harm to specific demographics.
Types of cancer with promising research
A number of clinical cancer types indicate supportive response to green tea consumption. Research suggests possible gains for:
Prostate Cancer:
Clinical trials display that green tea extract has lowered PSA levels for the meantime in patients waiting for prostatectomy. [28] However, the prolonged use of EGCG products among people did not gradually lower prostate cancer risk.
Breast Cancer:
Green tea drinkers, do show decreased breast cancer rates. Oddly enough, the meta-analysis of breast cancer studies noted that greater than three cups led to a 27% decrease in recurrence on average.
Digestive Tract Cancers:
Analyzing 27 studies on green tea and its potential impacts on upper gastrointestinal malignancies reveals possible preventative advantages
Why increasing the number of clinical trials is imperative.
Issues that current research has limits to solve are:
Study inconsistencies:
One review of 51 studies, with over 1.6 million participants included, resulted in conflicting findings [2]. While some studies suggested reduced risk of cancer, others did not showcase any risks or showcased an increase in risk for certain cancers.
Population differences:
Most studies focus on populations in East Asia who are known to have high consumption levels of green tea, thus limiting their results’ generalizability [15].
Methodological challenges:
Differences in measurement of tea drinking, study designs, and ensuring other extraneous variables don’t interfere make it hard to compare the results [14].
Above all, large scale randomized control trials are necessary specifically for:
- Current evidence showing various results for different types of cancers.
- The optimal dosage and duration of consumption needs to be determined.
- The interaction with other conventional treatments needs to be analyzed.
- Long term safety profiles need to be established [12].
Large scale clinical trials that are focused on specific mechanisms (for example the effect of green tea extract on breast cancer biomarkers in post menopausal women with high breast density) are currently underway [31]. In the meantime, research indicates that drinking green tea has not been shown to aid in cancer prevention, but drinking it in moderation seems to be safe [8]. There are debates surrounding, weight loss and longevity claims pertaining to the tea that stems from its consumption.
Research is mixed on whether green tea is effective for weight loss or prolonging life, which has led to more scrutiny on the theory behind these claims.
Conflicting weight loss studies analysis
Meta-analyses suggest that tea drinkers lose a small, but noticeable amount of weight. In a broad study, researchers reported that catechins led to a weight decrease of about 1.31 kg [33]. Inconsistent individual studies, however, also exist. Clinical trials with 937 postmenopausal women showed no significant change in weight, BMI, or waist circumference [34].
There seems to be an ethnic component that determines results. Asian subjects lost more weight (1.51 kg) compared to Caucasian subjects (0.82 kg) [33]. High caffeine consumption also seems to play a significant part – caffeine consumers (>300 mg daily) experienced less favorable outcomes (-0.27 kg) compared to low caffeine consumers (-1.60 kg) [33].
Metabolic rate effects: Minor or Major?
Research indicates that there are two key compounds in green tea that impact metabolism:
- Cleansers: North post transcriptional Cram fat oxidation mechanism processes
- Caffeine: Increases basal metabolic rates and the usage of energy [1]
The impact does, however, remain minor.
Research indicates that tea extract is associated with a little weight reduction over a period of time in overweight individuals which is not statistically significant [35]. Even with exercising, the advantages seem to be very small – research indicates that results are very small when measuring changes in body composition unless the individual was engaging in regular exercise [35].
Population studies on longevity: Correlation vs causation
There are some population studies which show possible relationships between drinking tea and life expectancy. In an observational study conducted over 8.7 years, 43,276 participants who drank 3-5 cups of tea a day lived approximately 2.24 years longer than those who did not. This was in comparison to non drinkers. [2]
In the same way, a study conducted over 15 years involving 164,681 adults in China showed that those who consumed green tea had lower mortality rates due to these reasons:
- For all causes
- Due to cardiovascular disease
- Due to cancer [36]
Regardless, researchers believe these results exhibit correlation rather than causation [37].
Numerous variables affect these correlations:
• Perceptions about tea or coffee consumption can vary greatly.
• Differences in cultural aspects such as cooking tea.
• The individual’s diet as a whole.
• Other lifestyle choices [37]
Interestingly, The inverse relationships with mortality were noted to be stronger among some particular populations.
Such facts were noticed among:
• People who don’t smoke.
• People who don’t drink alcohol regularly.
• People living in the countryside. [36]
Conclusion
The Data scientists collected is not consistent, One study showed green tea has more health benefits while the other suggests few benefits.
Some effects are deemed accurate while others need a bit more digging. Green tea has the most support when it comes to its antioxidant effects and cardio benefits, especially in regard to its EGCG content and the cholesterol levels it alters.
There is great potential in the brain function and mental health benefits, particularly from the combined action of L-theanine and caffeine. Laboratory studies show possible cancer fighting effects, but human trials are more mixed which necessitates further research.
The evidence for weight loss and longevity claims is still considered incomplete, as their benefits differ remarkably, by population and study conditions. The best approach is to treat green tea as one component of a healthy lifestyle rather than a magical answer for everything, which it certainly isn’t.
Recent evidence suggests getting the most health benefits from green tea requires an intake of 3-5 cups daily. This range ensure sufficient catechins and other helpful substances are included without too much caffeine. People have different reactions so it’s important to note that consistency, not amount, is key to healthier living.
Read More:10 Evidence-Based Benefits of Green Tea
