(I) Promoting Salivation to Quench Thirst and Relieving Heat and Summer Heat
It is recorded in “Tea Manual” that “People can quench their thirst by drinking genuine tea.” In “Daily Materia Medica”, it is stated that tea can “relieve restlessness and quench thirst”. In “The Outer Collection of Tea Manual” written by Sun Dahuai, it is said that “As for its functions of relieving restlessness, quenching thirst, rejuvenating the body and making one feel light, the benefits of tea are as miraculous as if by divine power.” It is common knowledge that drinking tea can relieve thirst. In the sweltering heat of midsummer, a cup of green tea can immediately make one feel saliva flowing in the mouth. Besides replenishing water for the human body with tea soup, it is also because polyphenolic compounds, free sugars, amino acids, vitamin C and saponin compounds in tea react with saliva in the mouth, which moistens the mouth, creates a cool feeling and also has an obvious thirst-quenching effect. Tea is also a beverage that can clear away heat and reduce fire. Li Shizhen, a famous ancient Chinese medical scientist, wrote in “Compendium of Materia Medica” that “Tea is bitter and cold, belonging to the extreme yin among yin, with a sinking and descending nature. It is most capable of reducing fire. Fire is the cause of all diseases. Once the fire is reduced, the upper part of the body will be clear!” From the perspective of traditional Chinese medicine, tea, especially green tea, is a cooling food that can clear away internal heat.
(II) Diuretic and Detoxifying Effects
It is widely known that drinking tea can act as a diuretic. Gu Yuanqing in the Ming Dynasty mentioned in “Tea Manual” that people can “benefit the urinary tract” by drinking genuine tea. Tea contains 2.5 – 5.0% caffeine, theophylline and theobromine. These alkaloids are a kind of diuretics, which can inhibit the reabsorption of renal tubules, increase the content of sodium and chloride ions in urine. These compounds can also stimulate the central nervous system, directly dilate renal blood vessels, increase the blood flow in the kidneys, and thus increase the filtration rate of glomeruli. Tea also has the effect of detoxification. The legend that Shennong used tea to detoxify mentioned earlier is the earliest record that tea can detoxify. In “General Principles of Materia Medica” written by Li Shizhen in the Ming Dynasty, it is recorded that tea can “relieve alcohol toxicity” and “detoxify various poisons”. The reason why tea can detoxify is related to the components such as caffeine and tea polyphenols it contains. Tannin in tea can combine with heavy metals or various alkaloid substances to form precipitates, thus having a detoxifying effect. Besides the detoxifying effect that occurs in the human body, tea can also react with some heavy metal elements (such as lead, zinc, antimony, mercury, etc.) existing in water quality. After being drunk into the human body, they are excreted out of the body through urination.
(III) Boosting Thinking and Refreshing the Mind
It is a common sense in life among Chinese people that drinking tea can refresh the mind. After intense work or labor, drinking a cup of tea can boost one’s spirit and relieve fatigue. Drinking a cup of tea while working in the office can improve work efficiency. There were also many such records in ancient China. Gu Yuanqing in the Ming Dynasty recorded in “Tea Manual” that drinking tea can make people “sleep less” and “benefit thinking”. It is recorded in “Shennong’s Food Classic” that “Long-term consumption of tea makes people strong and in a good mood”. For those who practice Buddhism in temples, dozing off is the most taboo. In order to refresh themselves and drive away sleepiness, they often rely on tea to achieve the purpose. For this reason, tea trees are usually planted around temples, and monks also drink tea.
(IV) Strengthening Teeth and Preventing Dental Caries
Tea trees are plants that can accumulate fluorine and are one of the plants with the highest fluorine concentration in the plant kingdom, which can be ten to hundreds of times higher than that of ordinary plants. Fluorine is closely related to dental health. Fluoride ions can promote remineralization, increase the hardness of tooth enamel and enhance the acid resistance of the tooth enamel surface. Because fluorine has such a tooth-strengthening effect, many countries add a certain amount of fluorine to tap water. Polyphenolic compounds in tea are effective compounds for tea’s anti-caries effect. How do tea polyphenol compounds play their anti-caries role? First, they can directly kill or inhibit cariogenic bacteria. Second, polyphenol compounds in tea can inhibit the adhesion of cariogenic bacteria on the tooth surface. Therefore, it can be seen that the anti-caries effect of tea is a comprehensive anti-caries effect jointly formed by fluorine in tea and polyphenol compounds in tea.
(V) Strengthening the Immune System
The human body has its own immune function to resist the invasion of foreign microorganisms and maintain the health of the body. This immune defense system forms immune proteins to identify pathogens invading the human body, and then white blood cells and lymphocytes in the human body produce antibodies and macrophages to carry out the task of surrounding and annihilating pathogens. Drinking tea can increase the number and activity of white blood cells and lymphocytes in the human body and promote the formation of interleukin in spleen cells, thus strengthening the immune function of the human body.
(VI) Preventing Aging
(VII) Antiviral Effect of Tea and Microorganisms
It has been reported in medical books as early as the Tang and Song Dynasties that tea can kill bacteria. There are many prescriptions composed of compound formulas for treating dysentery and cholera. Generally, redundant bacteria will die within 20 hours in tea juice, typhoid and dysentery bacteria can be killed within 8 – 11 hours, and cholera bacteria can be killed within 2 hours. Besides pathogenic bacteria, tea has a strong inhibitory effect on many pathogenic fungi that cause human skin diseases, such as Trichophyton tonsurans, Trichophyton gypseum, Trichophyton interdigitale and tinea fungi. Polyphenolic compounds in tea also have a strong bactericidal effect on many plant pathogenic bacteria, such as soft rot bacteria of vegetables, Ralstonia solanacearum of solanaceous plants, Pseudomonas syringae pv. cichorii causing leaf spot of chicory, and bacteria causing leaf spot of lettuce.
(VIII) Reducing Blood Lipids and Losing Weight
There are four reasons why drinking tea can promote human fat metabolism and reduce blood lipids: First, caffeine combines with substances such as phosphoric acid and pentose to form nucleotides, which play an important role in the metabolism of food nutrients, especially having a strong decomposing effect on fat. Second, caffeine has the function of stimulating the central nervous system, increasing the secretion of gastric acid and digestive juices, thus enhancing the absorption and digestion of fat by the human gastrointestinal tract. Third, catechin compounds in tea can promote the decomposition of human fat and prevent the accumulation of sterols and neutral fats in blood and liver. Fourth, chlorophyll in tea, on the one hand, can hinder the digestion and absorption of cholesterol by the gastrointestinal tract, and on the other hand, can destroy cholesterol that has entered the enterohepatic circulation, thus reducing the level of cholesterol content in the body.
(IX) Lowering Blood Pressure and Preventing Cardiovascular Diseases
(X) Eliminating Odor and Helping Digestion
Catechin compounds in tea have the following four effects on eliminating bad breath: ① Clearing the bad breath substances – methyl mercaptan in the mouth; ② Combining with the matrix of oral bacteria – amino acids; ③ Having a bactericidal and bacteriostatic effect on oral bacteria; ④ Purifying enzymes in oral saliva. Drinking tea can eliminate bad breath on the one hand and help digestion on the other hand. This is because tea contains aromatic substances. These substances can not only stimulate the secretion of gastric juice, help digestion and absorption, but also eliminate the dirt accumulated in the stomach, and relieve symptoms such as dry mouth and bad breath.
(XI) Lowering Blood Glucose and Preventing Diabetes
(XII) Improving Vision and Treating Ophthalmic Diseases
Carotene contained in tea is extremely important for the function of the eyes. Carotene, also known as provitamin A, will be converted into vitamin A in vivo, which can maintain the normal functional state of epithelial tissues, combine with proteins in the retina to form rhodopsin, and enhance the photosensitivity of the retina, so it has the effect of improving vision. In addition, vitamin B1 in tea is an important substance for maintaining nerve physiological functions, which can prevent blurred vision and dry eyes caused by optic neuritis.
(XIII) Radiation Protection
The effective components of tea for radiation protection are mainly tea polyphenol compounds, lipopolysaccharides, vitamin C, vitamin E and some amino acids, as proved by experiments. Its mechanism of action is also the detoxification effect produced in response to free radicals caused by radiation and resulting in peroxidation poisoning. Tea polyphenol compounds can resist oxidation and scavenge free radicals, thus achieving anti-radiation effects and acting as a radiation protective agent.
(XIV) Developing Intelligence and Regulating Body and Mind
Drinking tea can cultivate one’s temperament. A professor in China put forward that “Frugality cultivates virtue, beauty, truth and happiness. Be harmonious and sincere in dealing with the world and respect and love others.” Therefore, drinking tea not only plays a role in maintaining health from a pharmacological perspective but also plays a role in regulating body and mind from a psychological perspective.
(XV) Anti-cancer and Anti-mutation
The anti-cancer mechanism of tea mainly has the following seven pathways: 1. Antioxidant effect and scavenging free radicals; 2. Inhibiting the formation of carcinogens; 3. Inhibiting the carcinogenic process of carcinogens; 4. Inhibiting the proliferation of cancer cells; 5. Strengthening the immune function; 6. Inhibiting the covalent binding between oncogenes and deoxyribonucleic acid (DNA) in the human body. Because only when oncogenes bind to human DNA can the mutated genes enter the carcinogenic process and cause the proliferation of cancer cells, and the effective components in tea have the effect of inhibiting this covalent binding; 7. Inhibiting the initiating and promoting effects in the carcinogenic process.
