Polyphenols in tea. EGCG benefits of black and green tea

Polyphenols in tea. EGCG catechins benefits of black and green tea
Benefits of tea

History of tea consumption.

Tea consumption first documented in ancient China 5000 years ago.

Since then tea has become the number one beverage in the world. Nowadays, tea is the most popular beverage consumed by 2/3 of the world’s population on a weekly or daily basis.

Green tea is the most well-known tea around the globe. It’s the most-studied for health benefits, even for having anti-cancer properties as having chemopreventive benefits.

Polyphenols, Catechins, and EGCG in tea.

Polyphenols in tea are maybe the most important reason for the tea’s health effects.

Tea polyphenols are considered to contribute to the prevention of various degenerative diseases, such as cardiovascular diseases, and cancers. Additionally, green tea consumption may be beneficial in reducing the plasma concentration of cholesterol (1).

There are four types of polyphenols: flavonoids, stilbenes, phenolic acids, and lignans.

You can learn more about polyphenols, their health benefits, and all the food that contains them, here.

The most important thing to remember is that polyphenols are a group of chemical substances mostly present in plants. For that reason, only a whole food plant-based diet can provide us with an adequate amount of polyphenols.

The tea polyphenols are of flavonoid group, named catechins. Catechins are about 30% of the dry leaf weight from the tea plant (herbally named Camellia sinensis) (1).

Catechins can be analyzed further to EGCG, EGC, and EC. EGCG is the most abundant in tea leaves.

That acronyms come from epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and epicatechin (EC).

Tea is the most popular beverage in the world, second only to water. Its high consumption can greatly help in our daily polyphenol intake. A study measured that the consumption of cocoa, tea or coffee could easily increase the daily polyphenol intake by 500–1000 mg (17).

Tea and weight loss.

In a study, scientists provided rats with green and black tea. They found that rats significantly reduced (2,20):

  • body weight
  • plasma triglyceride
  • cholesterol
  • LDL-cholesterol

It is believed that the main reason green or black tea has powerful weight-loss benefits is EGCG. EGCG is a type of catechin. EGCG in tea has been studied many times for its role in weight loss.

In a study, EGCG decreased diet-induced obesity in mice. Scientists found that the EGCG managed it by decreasing energy absorption and increasing fat oxidation (2).

In another study, tea catechins prevented mice from gaining weight. Most importantly, tea catechins inhibited visceral and liver fat accumulation (2).

EGCG can also significantly reduce or prevent an increase in body weight in either lean or obese rats.

How EGCG in tea affect bodyweight loss?

Long-term consumption of green tea may be an ally against obesity. The most powerful chemical component in green tea is EGCG.

Green tea extract rich in catechins and caffeine can help on weight loss because it (2):

  • has thermogenic properties and
  • promotes fat oxidation

Interaction between catechin-polyphenols and caffeine is of huge importance for weight loss. Polyphenols and caffeine interaction increase and prolong thermogenesis in the body. This mechanism fights obesity more efficiently (2,21).

Does green tea increases metabolism or reduce appetite?

Recently, it has been shown in a double-blind, placebo-controlled study that consumption of a beverage containing green tea catechins and caffeine can increase energy expenditure by 4.6% for 24 hours. Such a boost in energy metabolism can sufficiently prevent weight gain (2,19).

Thermogenesis means heat production and is defined as the energy needed to digest, absorb, and dispose of the ingested nutrients.

It’s a normal by-product of the metabolic process.

Thermogenesis is adaptive. It is controlled by the brain. When we exposure to cold and to a certain diet, our brain detects it and decides what mechanisms to activate in order to control energy dissipation (18).

In summary, increased thermogenesis means increased metabolism.

Companies have created supplements that increase thermogenesis. They claim that such supplements increase metabolism, burn fat, and reduce appetite.

Why take a pill when there are other natural ways to lose weight effortlessly?

Just drink your tea…

Tea and longevity

In a study with 13-year follow-up data, there was found an apparent delay of death, either from cancer or all-cause deaths, when people had increased consumption of green tea, specifically in persons less than 79 years of age.

Scientists believe that daily consumption of green tea in sufficient amounts will help to prolong life by avoiding premature death, particularly death caused by cancer (2,22).

Another 8-year follow-up study was conducted by the Saitama Cancer Center in Japan.

Scientists studied the effects of green tea on human life in 8500 participants (2,23).

  • 3 cups: The average life span was 66 years for males who had more than 3 cups of green tea every day and 68 years for females.
  • 10 cups: The average life span was 70 years for males who had more than 10 cups of green tea per day and 74 years for females.

Scientists also found a decreased relative risk of death from cardiovascular disease, for people who used to consume more than 10 cups of green tea daily.

Tea polyphenols and cardiovascular diseases

A major risk factor for the development of heart disease is the elevated level of plasma cholesterol.

Luckily, epidemiological studies in Japan showed that green tea could lower cholesterol and also inhibit the process of atherosclerosis. Tea polyphenols appear to play an important role in the prevention of cardiovascular diseases (1).

Studies on animals have shown promising results as well. For instance, a study showed decreased atherosclerosis incidence by up to 63%, to animals, when green or black tea was providing (1).

Tea polyphenols protect us against oxidation. This mechanism has been proposed to contribute to the prevention of atherosclerosis and other cardiovascular diseases (2).

Tea polyphenols and cancer

Additionally, the cancer-preventive effects of green tea are widely supported by results from epidemiological, animal and clinical studies. 

Various animal studies have revealed that treatment with green tea inhibits tumor multiplicity in different organs. Green tea and EGCG polyphenols can inhibit the progression of carcinogenesis, as it has chemopreventive effects (1).

Antioxidant properties of green tea and EGCG polyphenols

Do you want good health? You better consume foods rich in antioxidants.

Green tea along with a whole food plant-based diet improves the overall antioxidative status and protects us against oxidative damage (1,15).

Antioxidant levels double when brewing tea for over 5 minutes.

In oxidation, our bodies produce free radicals. Free radicals are molecules that can cause damage to proteins, lipids, and DNA.

It’s crucial for our health, free radicals to be cleaned up. This job is done by antioxidants.

Several human diseases have a strong association with the oxidative damage in tissues, as there isn’t adequate consumption of antioxidants through food.

Such common diseases are cancer, heart disease, diabetes, Alzheimer’s disease, and also aging (1,10).

Organic polyphenols found in plants are known to have antioxidant activity.

For this reason, a diet rich in plants is required for good health.

More than 1,000 research articles may be found in the current literature with an emphasis on green tea as an antioxidant. The main ingredient for the antioxidant properties of green tea is believed to be a type of catechin-polyphenols named EGCG. EGCG has powerful antioxidant properties (1,11).

What to prefer? Green or Black tea?

Green tea, black tea, and oolong tea are all derived from the Camellia sinensis plant. There are no differences between green, black, and oolong tea except from the fermentation process.

All teas contain many important health-promoting compounds. The most significant of them are polyphenols though (1).

Green tea isn’t fermented. Contrary, black tea is completely fermented, and oolong tea contains a mixture of both fermented and non-fermented leaves.

In the production of black tea, the tea leaves are crushed. About 75% of catechins contained in the tea leaves undergo enzymatic transformation and partial polymerization.

The resulting black tea composition depends on the technics used. Black tea polyphenols composition varies with different preparations.

Approximately, black tea contains (2):

  • catechins (10–12%),
  • theaflavins (3–6%),
  • thearubigins (12–18%),
  • flavonols (6–8%),
  • phenolic acids (10–12%),
  • amino acids (13–15%),
  • methylxanthines (8–11%),
  • carbohydrates (15%),
  • proteins (1%),
  • mineral matter (10%), and
  • volatiles (<0.1%).

Also, tea leaves contain about 2–5% caffeine and much smaller quantities of theobromine and theophylline. Most of the catechin mass in the process of black tea manufacture is transformed into compounds called thearubigins (2)

Theaflavins are characterized by the bright red-orange color and contribute to the unique taste and color of black tea.

The amount of caffeine in tea beverage is determined by the (2):

  • leaf size,
  • the brewing time and the processing method, and finally
  • the temperature (2)

So what tea should I prefer? Green or black tea?

Maybe green tea it’s the better option.

A prospective nine-year study among 8,552 Japanese adults observed daily consumption tea habits. When people consumed more than ten cups of green tea daily delayed cancer onset by up to 8.7 years when compared to patients consuming fewer than three cups daily.

Such protective effects are less frequently in European populations where they use to consume black tea (2,24).

How much tea should we consume daily?

A study tried to find out how different amounts of green tea affect our bodies. Scientists measured the antioxidant capacity of participants’ plasma 60 and 120 minutes after the tea consumption (1,13).

  • 150 ml of green tea, were not enough to increase significantly the antioxidant capacity of participants,
  • 300 ml of green tea, raised antioxidant capacity by 7% after 60 min and by 6.2% after 120 min.
  • 450 ml of green tea gave the best results though. Antioxidant capacity was increased by 12% the first 60 min and by 12.7% after 120 min.

As you can see the bigger the dose of green tea, the better the results. What will happen if we consume more than half a liter of tea daily though?

Another study that tried to find the effect of green tea in human health, provided participants with 1 lt of green tea daily for a month. Scientists observed a rise in the antioxidant capacity of participants, and they suggested that drinking green tea has a beneficial effect, by reducing the oxidative stress in the body, protecting us for oxidative stress diseases. No side effects observed (1,12).

A third study measured the effect of different amounts of decaffeinated green tea solids dissolved in 500 ml of water. After the consumption of tea, scientists measured the maximum plasma concentration of the three tea catechins: EGCG, EGC, and EC (14). 

They found that consumption of:

  • 1.5 gr of decaffeinated green tea solids, didn’t increase significantly the catechins in the body of participants.
  • 3.0 gr of decaffeinated green tea solids, increased the maximum plasma concentration of catechin values 2.7 – 3.4 fold.
  • 4.5 gr of decaffeinated green tea solids, did not increase the maximum plasma concentration of catechin values significantly. That’s probably a saturation phenomenon.

The plasma concentrations of EGCG, EGC, and EC catechins reached peak levels between 1.5 and 2.5 h in almost all of the participants. After that point catechins in the blood started to decline. Most tea catechins are cleared from the body in about 10 hours. After 24 hours catechins were undetectable in the blood (14).

Keeping that in mind, 3 g of green tea solids may be an optimal dose.

Higher doses of tea may not give a significantly higher blood level of tea catechins. (14)

In 2018, the European Food Safety Authority Scientific conducted a study about the maximum safe dose of green tea catechins (25).

The scientists considered the possible association between the consumption of high amounts of EGCG, the most relevant catechin in green tea, and hepatotoxicity, meaning chemical-driven liver damage.

The mean daily intake of EGCG from green tea consumption ranges from 90 to 300 mg/day, but heavily tea consumers can reach up to 866 mg EGCG/day.

The committee concluded that catechins from green tea infusion, prepared in a traditional way, are in general considered to be safe (25).

Maybe there are some cases with people with liver problems taking EGCG supplements.

Supplements can provide a daily dose of EGCG up to 1,000 mg/day.

The committee concluded that there is evidence that the intake of doses equal or above 800 mg EGCG/day taken as a food supplement has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control (25). Elevated transaminase levels can be caused by liver disease.

1 g of decaffeinated green tea solids powder contains about (14):

  • 73 mg of EGCG,
  • 68 mg of EGC,
  • 22 mg of ECG, and
  • 25 mg of EC.

To prepare one cup of green tea, we use about 1.8 to 3 g of green tea solids. This means that we consume about 200 mg of EGCG per cup of tea.

Practically…

How many cups of tea daily?

In order to avoid any unwanted liver issues, 4 cups or 1 lt of tea daily should be your limit.

Remember… That’s for safety reasons, especially for people with liver issues.

There are populations that consume more than 10 cups a day, without any implications. Japanese studies have been conducted for thousands of people, consuming more than 10 cups of tea daily, without side effects.

When should I consume tea?

Just remember:

  • Concentrations of EGCG, EGC, and EC catechins reach peak levels in about 2 h after consumption.
  • 3.0 gr of green tea solids is the optimum dose. More will not benefit you, as saturation occurs.
  • Aim to 4 cups daily.
  • Tea contains caffeine, so it’s better consumed in the morning.

For these reasons, start your day with a cup of tea. Drink the next cup after 2-3 hours. Aim to 4 cups in total.

So, for example, you can drink a cup of tea at 8 am, 11 am, 14 am, and 17 am.

The most important thing to remember is that you should wait some hours before the next cup of tea, to take maximum advantage of the catechins in it.

Sources:

  1. NCBI– PMC: Tea polyphenols, their biological effects and potential molecular targets
  2. NCBI– PMC: Tea polyphenols for health promotion
  3. NCBI– PMC: Recent advances on tea polyphenols
  4. NCBI- Pubmed.gov: Cancer chemoprevention with dietary phytochemicals.
  5. NCBI- Pubmed.gov: The effects of plant flavonoids on mammalian cells: implications for inflammation, heart disease, and cancer.
  6. NCBI- Pubmed.gov: Cancer-preventive effects of drinking green tea among a Japanese population.
  7. NCBI- Pubmed.gov: Influence of drinking green tea on breast cancer malignancy among Japanese patients.
  8. NCBI- Pubmed.gov: The green tea polyphenol (-)-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage.
  9. NCBI- Pubmed.gov: Effect of increased tea consumption on oxidative DNA damage among smokers: a randomized controlled study.
  10. NCBI- Pubmed.gov: Oxidative stress profiling: part I. Its potential importance in the optimization of human health.
  11. Prevention of reactive oxygen species-induced oxidative stress in human microvascular endothelial cells by green tea polyphenol.
  12. The effect of green tea on oxidative stress.
  13. NCBI- Pubmed.gov: In vivo antioxidant effect of green tea.
  14. Blood and urine levels of tea catechins after ingestion of different amounts of green tea by human volunteers.
  15. Effectiveness of moderate green tea consumption on antioxidative status and plasma lipid profile in humans.
  16. Risk of melanoma and vitamin A, coffee and alcohol: a case-control study from Italy.
  17. British Journal of Nutrition: Dietary reference intake (DRI) value for dietary polyphenols: are we heading in the right direction?
  18. Thermogenesis: Thermogenesis is defined as the dissipation of energy through the production of heat and occurs in specialized tissues including brown adipose tissue and skeletal muscle.
  19. Effect of a thermogenic beverage on 24-hour energy metabolism in humans.
  20. Mechanisms of hypolipidemic and anti-obesity effects of tea and tea polyphenols.
  21. Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity.
  22. NCBI- Pubmed.gov: Can teatime increase one’s lifetime?
  23. Japanese green tea as a cancer preventive in humans.
  24. Critical Reviews in Food Science and Nutrition: Antioxidants in tea.
  25. European Food Safety Authority: Scientific opinion on the safety of green tea catechins.