Health benefits of tea. It’s rich in polyphenols!

Drinking up to 4 cups of tea a day is good for you. Tea has many health benefits, due to its high polyphenol content.

The health benefits of tea come from its high polyphenol content

Green tea may have many health benefits due to its high polyphenol content. In fact, tea is among the top-100 high-polyphenol foods.

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).

The tea polyphenols are of flavonoid group, named catechins. Catechins are about 30% of the dry leaf weight from the tea plant (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 help us boost our daily polyphenol intake. A study measured that the consumption of cocoa, tea or coffee could easily increase the daily polyphenol intake by 500–1,000 mg (17).

Tea may support weight loss

Drinking tea may be beneficial for weight loss. EGCG in tea may decrease energy absorption, while promoting fat burning (2).

Furthermore, catechins of tea may inhibit visceral and liver fat accumulation.

Moreover, caffeine in tea may play a key role in weight loss. The interaction of polyphenols with caffeine may prolong thermogenesis in the body (2,21).

Green tea can increase energy expenditure by 4.6% for 24 hours (19)!

Tea & 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 used to drink high amounts of green tea.

Scientists believe that the daily consumption of green tea in sufficient amounts will help 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 8,500 participants (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 & cardiovascular diseases

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

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% in 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 & 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 green tea may inhibit 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

Green tea improves the antioxidative status of the body and protects us against oxidative damage (1,15).

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

Chronic oxidative stress may cause diseases, such as cancer, heart disease, diabetes, Alzheimer’s disease, and also premature aging (1,10).

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).

Does green or black tea have the most health benefits?

Green tea, black tea, and oolong tea are all derived from the Camellia sinensis plant. Only the fermentation process is different among these types of tea.

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

Green tea isn’t fermented. On the contrary, black tea is completely fermented. 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%)

Also, tea leaves contain about 2–5% caffeine.

Green tea may have more health benefits, though. According to a study, when people consumed more than ten cups of green tea a day delayed cancer onset by up to 8.7 years when compared to patients consuming fewer than three cups. Such protective effects are less common in European populations where they consume black tea (2,24).

How much tea should we consume a day?

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 significantly increase the antioxidant capacity of participants,
  • 300 ml of green tea, raised the antioxidant capacity of the body by 7% after 60 min and by 6.2% after 120 min.
  • 450 ml of green tea gave the best results. Antioxidant capacity was increased by 12% the first 60 min and by 12.7% after 120 min.

Another study, that tried to find the effect of green tea in 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. No side effects observed (1,12).

Therefore, the bigger the dose of green tea, the better the results.

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 g of decaffeinated green tea solids, didn’t increase significantly the catechins in the body of participants.
  • 3.0 g of decaffeinated green tea solids, increased the maximum plasma concentration of catechin values up to 3.4-fold.
  • 4.5 g of decaffeinated green tea solids, didn’t increase the maximum plasma concentration of catechin values significantly. Probably due to saturation.

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 have more health benefits (14).

In 2018, the European Food Safety Authority Scientific conducted a study about the maximum safe dose of green tea catechins. The scientists considered the possible association between the consumption of high amounts of EGCG and hepatotoxicity, meaning chemical-driven liver damage.

The mean daily intake of EGCG from green tea consumption ranges from 90 to 300 mg per day. But, heavily tea consumers can reach up to 866 mg of EGCG per day. The committee concluded that catechins from green tea infusion, prepared in the traditional way, are generally considered safe (25).

So, people with liver problems should consult their physician before drinking tea. or before taking EGCG supplements.

The committee concluded that there is evidence that the intake of doses equal or above 800 mg of EGCG per day, taken as a food supplement, have been shown to induce a statistically significant increase of serum transaminase in treated subjects, compared to control. 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.

Hence, in order to avoid any side effects, better consume up to 4 cups or 1 lt of tea per day.

Healthy people are rather unlikely to have any side effects, even from much higher doses, though. 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.

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.