Catechins are active compounds derived from the purification of plant extracts, belonging to the group of polyphenols.
The plant with the highest concentration of catechins is green tea, known by its Latin name Camellia sinensis. Green tea contains various types of catechins. The health benefits of green tea, one of the most commonly consumed beverages worldwide, mainly arise from the presence of these herbal actives.
During the growth, fermentation, and processing of tea, changes occur in the variety and quantity of bioactives present in the tea. These changes and substances formed are used in the treatment of many diseases.
It is noted that catechins, among the tea polyphenols, contribute to the prevention of diseases such as obesity, diabetes, cardiovascular diseases, and cancer through their antioxidant activity. Additionally, these components are said to have antiviral, antibacterial, and protective effects against neurological diseases. This article aims to examine the composition of tea and its effects on health.
What is Green Tea?
The green tea plant is Camellia sinensis of the Theaceae family. It is a short, perennial shrub that grows in humid climates, does not shed its leaves, and remains green throughout the year. The tea plant is cultivated in more than 40 countries, with significant production taking place in Turkey, China, Sri Lanka, Indonesia, Japan, India, Taiwan, and central African countries.
What Are the Components of Tea?
The chemical composition of tea leaves can vary depending on the origin, age, processing method, and processing duration of the tea. The most important components are catechins (polyphenols) and caffeine. In addition, the composition of smaller amounts is detailed in Table 1. The quantities of components in 100 grams of tea consumed after adding 15 grams of tea leaves to one liter of water and steeping for five minutes before straining are listed.
Content of Catechins (Polyphenols)
Fresh tea leaves contain a wide range of phenolic compounds. These include catechins, flavonols, proanthocyanidins, and phenolic acids from flavonoids. Depending on the production of black tea, oolong tea, and green tea, the fermentation of catechins is carried out by endogenous enzymes polyphenol oxidase and peroxidase. During fermentation, catechins oxidize to form dimeric and oligomeric compounds such as theaflavins, theasitrins, theasinensins, theanaptokinones, and thearubigins.
Catechins are more abundant in green tea, while the fermentation process in black tea replaces these catechins with theaflavins and thearubigins. These components also give the tea its characteristic aroma and color.
The most abundant catechin found in green tea is epigallocatechin gallate (EGCG), followed by epicatechin gallate (ECG), epigallocatechin (EGC), and epicatechin (EC). All of these are collectively referred to as catechins.
In addition to these, tea leaves contain hydrolyzable tannins of phenolic acid derivatives (ellagitannins and gallotannins), which are associated with the prevention of cancer and cardiovascular diseases due to their antioxidant properties. Another phenolic acid derivative, strictinin, is an important component particularly associated with allergic diseases. Strictinin is found in both green and black tea, and its concentration varies depending on the maturity of the leaves.
Caffeine Content
| Components | Amount |
| Protein (g) | 0.1 |
| Fat (g) | Trace amount |
| Carbohydrate (g) | Trace amount |
| Sodium (mg) | Trace amount |
| Potassium (mg) | 27 |
| Calcium (mg) | Trace amount |
| Magnesium (mg) | 2 |
| Phosphorus (mg) | 2 |
| Iron (mg) | Trace amount |
| Copper (mg) | 0.01 |
| Zinc (mg) | Trace amount |
| Chlorine (mg) | 1 |
| Manganese (mg) | 0.15 |
| Selenium (mcg) | Trace amount |
| Iodine (mg) | Trace amount |
| Thiamine (mg) | Trace amount |
| Riboflavin (mg) | 0.02 |
| Niacin (mg) | 0.2 |
| Vitamin B6 (mg) | Trace amount |
| Vitamin B12 (mcg) | 0.2 |
| Folate (mcg) | 3 |
| Pantothenate (mg) | 0.04 |
| Biotin (mcg) | 1 |
Caffeine is one of the main alkaloids found in tea, and its amount can vary between 1.5-5%. The caffeine content in one cup (237 ml) of green tea is approximately 30 mg, while in black tea, it is approximately 50 mg.
Table 1. Components of 100 grams of consumable tea
What Are the Uses of Tea in Human Health?
It is used in many fields. The most common disease it treats is warts, particularly due to its antiviral effect against HPV, known as warts. The most serious warts are anal and genital warts, and the cream form is used for the treatment of warts in these areas.
The Relationship Between Tea and Catechin with Health
The belief in the relationship between tea and health dates back to the 19th century. The health benefits of tea are generally associated with the catechins it contains.
It is claimed to play an important role in the prevention and treatment of viral diseases (the most commonly used disease is HPV), cardiovascular diseases, obesity, diabetes, oxidative and inflammatory diseases, bacterial diseases, cancer, and neurological diseases. These are listed in Figure 1.
Catechin Antiviral and Antibacterial Effects
Scientific studies have shown that green tea catechins can exhibit antiviral effects through the inhibition of HPV (human papillomavirus, wart, condyloma) and influenza virus replication. Additionally, it is known that green tea catechins have an inhibitory effect on Herpes simplex virus infection.
The potential health effects of tea, as mentioned earlier, are due to the phenolic compounds it contains. From these phenolic compounds (catechins), it has been shown that green tea, particularly rich in EGCG and EGC, has antimicrobial, antifungal, and antiviral effects.
In a study on this matter, the potential antimicrobial effect of green tea, especially against Escherichia coli, was determined. In another study aimed at testing the antibacterial activity of green tea leaf extracts against various bacteria isolated from environmental sources, the antibacterial activity of green tea was determined.
In a study investigating the role of non-polymeric phenolic and polymeric tannin components of green, black, and different herbal teas obtained from Camellia sinensis, it was found that these components have strong antioxidant and antibacterial properties.
Effect of Catechins on Heart Diseases
Cardiovascular diseases (CVDs) are a broad group of diseases covering all diseases of the heart and blood vessels, including coronary heart disease, stroke, rheumatic heart diseases, cerebrovascular diseases, peripheral artery diseases, hypertensive diseases, and arrhythmias.
It is generally known that tea consumption reduces the risk of cardiovascular disease. In a meta-analysis, it was stated that the results were not definitive regarding the relationship between tea consumption and coronary heart disease and stroke, but it showed a protective effect against myocardial infarction.
The positive effect of tea consumption on these diseases is explained by the antioxidants in its structure. It is reported that flavonoids in tea reduce the risk, but the mechanism of action is not yet completely clear. Flavonoids are reported to inhibit low-density lipoprotein (LDL) oxidation, reduce cholesterol absorption from the intestine, reduce platelet aggregation, and be effective in blood pressure.
In a study involving 48 healthy adults conducted as a randomized, double-blind, placebo-controlled trial, individuals were divided into 4 groups. The first group was given 250 mg of caffeine, the second group was given 200 mg of theanine, and the third group was given caffeine and theanine as capsules. The fourth group was the placebo group. It was found that theanine in tea works as an antagonist to caffeine and lowers blood pressure.
Effects of Catechins on Obesity
Obesity and the associated health problems continue to be major health issues worldwide. Tea consumption is one of the factors that affect appetite, nutrient absorption, and thermogenesis, which are related to body weight loss. Epidemiological and randomized controlled intervention studies show an inverse relationship between tea consumption and body fat percentage and waist circumference.
The relationship between green tea and obesity is related to the effects of catechins on thermogenesis and substrate oxidation, as well as changes in appetite control, regulation of hepatic lipid metabolism enzymes, and decreased nutrient absorption being possible other mechanisms of action. The sympathetic nervous system (SNS) plays a major role in regulating energy expenditure and lipolysis.
Norepinephrine (NE), a key player in the SNS, increases energy expenditure and fat oxidation. Catechins can extend the action of NE released sympathetically into the synaptic cleft by inhibiting catechol O-methyl transferase (COMT), an enzyme that reduces norepinephrine. Additionally, caffeine found in green tea can also affect the SNS and produce similar effects.
Therefore, the combination of catechins and caffeine can affect energy expenditure and lipolysis synergistically. Low liver fatty acid oxidation increases appetite. Catechins are reported to increase hepatic fat oxidation, which can lead to changes in appetite. However, experimental studies on this topic have yielded different and conflicting results. Additionally, catechins can affect amylase and glucosidase activity, inhibiting glucose absorption.
It is reported that the amount of plant material in prepared tea, brewing time, and water temperature can affect the composition of bioactive components. It is indicated that these bioactive components may have different effects depending on whether tea is consumed as a beverage or taken as a supplement. Therefore, more research is needed on the relationship between the amount of bioactive components in green tea and obesity.
The Effect of Catechins on Diabetes
The prevalence of diabetes is increasing day by day. However, it is known that this situation can be prevented by developing healthy lifestyle behaviors. It is reported that coffee and tea consumption have an inverse relationship with the risk of diabetes. Tea consumption is associated not only with reducing the risk of diabetes related to low body mass index (BMI) but also with its effect on amylase.
Tea polyphenols can slow down the digestion of starch, thereby reducing sudden increases in serum glucose [45, 46]. A study conducted in Singapore showed an association between regular consumption of coffee and black tea and a low risk of diabetes, while no association was found with green tea. It is thought that this effect is due to the caffeine found in black tea [47].
Another retrospective cohort study showed that green tea intake was associated with a lower risk of diabetes compared to black tea [48]. In a study conducted with 5823 non-diabetic adults examining the relationship between coffee and tea consumption and the risk of type 2 diabetes, it was concluded that coffee and tea consumption were not associated with diabetes incidence.
The Effect of Catechins on Inflammation
Many pathological conditions with the presence of acute or chronic inflammation cause significant changes in metabolic and biochemical processes in the organism. Nutrition plays an important role in the development and resolution of these processes.
It is known that the intake of flavonoids such as flavonols, anthocyanins, and isoflavones found in tea is negatively associated with the concentration of C-reactive protein (CRP), which is an important indicator of inflammation [30, 51].
In an in vivo study with mice with spinal cord injury, EGCG application was found to suppress inflammatory cytokines and have a protective effect in this direction. Another study with mice showed that 10 mg/kg/day of EGCG treatment for 30 days significantly reduced the levels of inflammatory cytokines and oxidative stress.
The Effect of Tea on Cancer
In the relationship between tea and cancer, EGCG and theaflavin, which are found in the composition of tea and exhibit antioxidant properties, stand out. These components can prevent the formation, growth, and proliferation of cancer cells, particularly due to the antioxidant property of tea.
It is reported that the polyphenols found in green tea, in particular, can inhibit angiogenesis. While tea polyphenols act in this way in the cancer cell cycle, it is stated that these effects do not occur in normal cells.
The pathways through which EGCG is effective in cancer cells are summarized as follows: mitogen-activated protein (MAP) kinases and activator protein-1 (AP-1), nuclear factor-kB (NF-kB) signaling pathway, epidermal growth factor receptor (EGFR) mediated pathways, insulin-like growth factor (IGF) -1 mediated signal transduction pathways, proteasome activities, matrix metalloproteinase (MMP) activities, and induction of apoptosis, leading to cell cycle arrest.
In studies examining the relationship between green tea and cancer, it has been found that as green tea consumption increases, the risk of different types of cancer such as prostate, breast, throat, and stomach cancer decreases [59-61].
In a study with human prostate cancer cells (PC-3), it was found that application of 0-50 μM EGCG for 48 hours to these cancer cells exhibited inhibitory effects on cell proliferation.
In a study with MDA-MB-231 human breast cancer cell line, it was observed that application of 50-80 μg/mL EGCG for 24 hours reduced MMP-9 expression, leading to induction of cell apoptosis. Another study with gastric cancer cells also determined that EGCG application induced cell apoptosis.
The Effect of Catechins on Oral Health
Dental caries and other oral diseases are among the most common chronic diseases, especially in children. Streptococcus mutans (S. mutans) and Lactobacillus are the main bacterial agents in the development of cavities. It is especially reported that green tea is an effective substance in preventing dental caries.
As in other health problems, catechins are responsible for many beneficial properties in oral health (dental caries, oral mucosa). In many studies, green tea has been shown to inhibit the growth of Streptococcus agent, prevent bacterial adhesion to tooth enamel, and prevent dental caries formation as a glucosyltransferase and amylase inhibitor.
In a study, it was found that green tea increased oral peroxidase activity and provided more protection against oxidative stress in the oral cavity. In a study comparing the effect of green tea mouthwash with sodium fluoride mouthwash on saliva Streptococcus mutans and Lactobacillus levels in children, it was observed that green tea mouthwash significantly reduced the number of saliva S. mutans and Lactobacillus colonies, while causing fewer side effects than sodium fluoride.
Similarly, in other studies, it has been shown that drinking tea and coffee significantly inhibits dental plaque formation and also reduces S. mutans and Lactobacillus in dental plaque and saliva.
Furthermore, another study indicated a relationship between green tea consumption and reduced tooth loss rate. As a result, it is reported that green tea products can be effectively used in the prevention and treatment of many oral and periodontal diseases.
The Relationship Between Catechins and Bone Health
Genetic factors, early menstruation, nutrition, low levels of physical activity, calcium, and vitamin D deficiency are among the factors that affect bone health.
Knowing the risk factors is important for preventing and treating bone health problems throughout life. Nutrition is one of the modifiable risk factors. Recently, green tea has been emphasized in relation to bone health in terms of nutrition.
It is believed that green tea positively affects bone health by reducing oxidative stress and inflammation. In women experiencing decreased bone density during menopause, green tea polyphenol supplementation and Tai Chi practice have been shown to increase bone formation biomarkers and improve bone turnover rate.
Another study with mice also found positive effects of green tea polyphenol supplementation on bone health. It is believed that green tea achieves this effect by increasing antioxidant capacity and suppressing inflammation.
In another study, an increase in coffee and tea consumption was found to raise circulating levels of vitamin D independently of physical activity, sun exposure, age, gender, and BMI.
A study on oolong tea concluded that drinking oolong tea may help prevent bone loss in menopausal Chinese women.
The Effect of Catechins on Neurological Diseases
The prevalence of neurodegenerative disorders is increasing over time. EGCG found in green tea can affect various neurological functions. Therefore, it is anticipated that green tea polyphenols may provide protection against Parkinson’s and Alzheimer’s diseases, and other neurodegenerative diseases.
In a cohort study, tea consumption was associated with a lower prevalence of cognitive impairment in Chinese adults, with black and oolong teas showing the most significant effects. In another cohort study, it was found that green tea consumption was associated with a lower frequency of depressive symptoms in the elderly.
Additionally, it is believed that theanine may have anti-stress effects by preventing cortical neuron excitation and reducing psychological and physiological stress responses.
Summary of Green Tea and Catechins
The amounts of bioactive components in tea can vary depending on the differences in tea processing. In black tea, theaflavins and thearubigins are more abundant due to the fermentation process, while in green tea, which does not undergo fermentation, different catechins such as EGCG, ECG, EGC, and EC are found in higher amounts.
While various studies in recent years have yielded different results, tea can be effective in the prevention and treatment of many diseases. The most significant mechanism of action on health is believed to be the oxidative enzyme inhibition of the polyphenols (catechins) present in its composition.
Thus, it can be used in the prevention and treatment of diseases such as cardiovascular diseases and different types of cancer. Additionally, it can have positive effects on diabetes and obesity through its effects on carbohydrate and lipid metabolism.
While various studies mention the anti-inflammatory, antimicrobial, and antiviral effects of tea, there are also many studies showing its significant role in neurological and psychological diseases. To address conflicting results, more experimental human studies are needed that take into account individual differences and compare tea amounts and preparation methods.
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