Tea and health
It’s said that it was the Chinese Emperor Shen Nong (2737 BC) who discovered the beneficial properties of tea leaves set in infusion and who consequently fostered the cultivation of Camellia Sinensis. From 200 BC tea was included in the traditional herbals as a plant useful for the treatment of fatigue and digestive disorders. There is a Chinese proverb that maintains that “A cup of tea a day keeps the doctor away”, and there is no doubt that its salubrious properties combined with the pleasant flavour of the drink have contributed to its popularity all over the world. Ongoing research in the medical sphere has meant that in recent decades it has been possible to identify the main chemical constituents contained in tea leaves, thus underscoring the traditionally known properties and also discovering new ones.
The data in literature, combined with in vitro and in vivo experiments appear to attribute properties beneficial to the health of the organism to the following substances contained in tea.
METHYLXANTHINES
The content of methylxanthines (caffeine, theobromine and theophylline) varies depending on the type of tea, the botanical variety, the temperature of the water used for the infusion and the duration of the infusion itself. On average, black tea contains mainly caffeine, while the other two xanthines are contained in greater quantities in green teas etc. As compared with coffee, tea contains less caffeine: a cup of around 150 cc of strong black tea contains 40 mg of caffeine and a cup of green tea contains 20 mg, as against the 100-125 mg of a 40 cc cup of coffee. The principal effect attributed to caffeine is its action as a stimulant to human mental faculties, while it also reduces the impression of fatigue. In addition, it increases renal circulation and the number of glomeruli, thus stimulating diuresis. Normally an adult can consume up to 400 mg of caffeine a day without any adverse effects such as general toxicity, cardiovascular effects and mood swings.
PHENOLIC COMPOUNDS
Over 80% of phenols are represented by flavonols (catechins). In black teas the processing modifies the qualitative and quantitative composition of the phenols, oxidising them enzymatically into theaflavin and thearubigin, which give the beverage its characteristic aroma and amber colour. The teas with the highest phenol content are green, white and semi-fermented teas. The most important of the catechins of tea is EGCG, epigallocatechin gallate. In addition to giving the tea infusion its typical astringent flavour, the catechins also have the following properties: • they are antioxidants. • they lower the level of LDL cholesterol (bad cholesterol) and triglycerides (fats in the blood), thus reducing the risk of cardiovascular disease. • they have a preventive effect on certain tumours. • they appear to have an inhibiting effect in relation to nicotine and reduce addiction. • they reduce glucose in the intestine and inhibit alpha amylase which is responsible for raising the glucose level in the blood after meals. • they reduce blood pressure: those suffering from high blood pressure are advised to preferably drink green tea with a low caffeine content (since caffeine has a hypertensive effect). • they have an antimicrobial effect on streptococcus, which is responsible for dental caries: studies show that this effect is more potent in semi-fermented teas. • they have a calming effect on the mucous of the stomach and the intestine, and an anti-bacterial effect on the bacteria responsible for diarrhoea.
VITAMINS
The water-soluble vitamins not destroyed by heat present in green tea are B1, B2 and B6. • B1 stimulates the metabolism of carbohydrates to supply energy to the brain. • B2 serves for the maintenance of the nerve fascia and to promote the metabolism of fats and carbohydrates. • B6 helps in the maintenance of skin and hair. Green tea is also rich in vitamin C, which strengthens the immune system against the attack of free radicals: this substance is water-soluble but is also affected by heat so that unfortunately in very hot water part of it is destroyed.
AMINO ACIDS
Among the amino acids, the essential constituents of proteins, that of greatest interest is Theanine (gamma-glutamylethylamide), with a higher percentage in green teas. Theanine can pass through the blood-brain barrier, favouring the release of neurotransmitters in the brain that have a "calming" action, thus inhibiting the effects of caffeine on the central nervous system. It also appears to prevent ischemic neuronal damage.
MINERALS
Green tea contains many minerals (4-5% of the dry weight of the fresh leaves). Potassium is present in high concentrations, followed by Calcium, Magnesium, Zinc, Manganese and Fluoride. • Potassium is important for the maintenance of normal heart rate and for the transmission of electrical impulses. • Zinc plays a part in the process of wound healing and strengthens the immune system. • Calcium and Magnesium are essential components of bones and teeth. • Manganese activates the enzymes responsible for the formation of bones, blood clotting and the metabolism of carbohydrates and fats. • Finally, Fluoride prevents dental caries as well as being an important component of bones and nails.
CONCLUSIONS
In conclusion, we can say that green, white and semi-fermented or oolong teas, and the Pu-Erh in view of its special processing, are those richest in beneficial substances for the organism. To reap the full benefit of the health-giving properties of tea, a consumption of 3 cups a day is normally recommended. Instead the only tea that allows us to take in 100% of the substances contained in it is the Japanese green Matcha, which has been used for centuries in Japan in the tea ceremony. Unlike all the other types of tea, Matcha is drunk in the form of powdered tea leaves mixed with water, and not as an infusion: this means that we benefit fully from all the substances that green tea is rich in. All the data provided here have been taken from a study carried out by the Department of Pharmacy of the University of Florence in collaboration with the company Snak srl - La Via del Tè. (An estimation of the assumed amount of catechins, xantines and theanine of several commercial representative types of tea, Department of Pharmaceutical Science, University of Florence, 2005).
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