What are the characteristics of green tea?
Latin name: Camellia sinensis L.
Botanical family: Theaceae
Producer organ: Leaf
How does tea work?
All teas contain caffeine and polyphenols (antioxidants from the flavonoid family). Caffeine is a substance of the methylxanthine family found in a wide range of plants: coffee, cocoa, kola, guarana, maté, etc. Caffeine stimulates the nervous system, increasing alertness and mental concentration. It reduces appetite, slightly increases basal metabolism (the body's energy expenditure at rest) and stimulates urine production.
Tea is rich in polyphenols: catechins (in particular, epigallocatechin-3-gallate or EGCG), theaflavins, thearubigins and others. These substances are antioxidants that can protect cells from chemical aggression. In cultured cells, EGCG has been shown to inhibit the growth of several types of cancer cells. This effect is thought to be linked to its antioxidant properties and its ability to inhibit an enzyme required for cancer cell growth, urokinase.
The effect of tea in preventing cavities may be linked to catechins, but also to its high fluoride content.
How effective is tea?
Starting at 60 mg for adults, caffeine intake stimulates intellectual capacity and urine production. The effects of caffeine on appetite and basic metabolism are limited, and disappear in people who consume it regularly. No long-term studies confirm any lasting effects of caffeine or tea on weight loss.
Studies on the preventive properties of tea in relation to cardiovascular disease or cancer have produced contradictory results. These are essentially observational studies which show (or not) a lower risk of developing these diseases in people who spontaneously consume large quantities of tea. But the influence of other factors (diet or healthier lifestyle in general) is almost never taken into account. In the context of cancer prevention or treatment, no study has clearly shown any benefit from tea consumption. Studies are currently underway in the United States to assess its action in the treatment of skin cancer.
Studies conducted on the effects of tea in preventing dental caries warrant larger-scale studies to confirm the benefits observed. Other proposed uses for tea have not been scientifically evaluated.
Tea and precautions for use :
- People with heart problems, insomnia, anxiety disorders, high blood pressure, stomach or kidney problems, or osteoporosis should limit their consumption of tea and caffeine.
- Diabetics should also avoid consuming large quantities of tea or caffeine, as the latter appears to raise blood sugar levels, particularly at the end of the day.
- Excess caffeine has a number of undesirable effects: nervousness, agitation, anxiety, palpitations, insomnia, stomach irritation, diarrhoea, etc. Regular use of high doses of caffeine leads to dependence, and withdrawal from caffeine causes headaches, drowsiness, nervousness, anxiety and irritability. In extreme cases, an overdose of caffeine can cause serious muscular disorders (rhabdomyolysis).
- Caffeine can interact with many other substances. The main caffeine interactions are with certain antibiotics, theophylline and products containing ephedra.
- Certain quinolone antibiotics (ciprofloxacin, enoxacin, norfloxacin) and, to a lesser extent, alcohol, female hormones and contraceptive pills slow down the elimination of caffeine and may increase its adverse effects. Theophylline, a substance used to treat asthma, has the same adverse effects as caffeine. Taking them together increases the risk of palpitations, excitement, tremors, etc.
- Caffeine-containing products should never be taken with plants containing amphetamine-like stimulants, such as ephedra (Ephedra sinica, which contains ephedrine) or bitter orange (Citrus aurantium, which contains synephrine), as these increase the risk of vascular accident (myocardial infarction). Caffeine also increases the absorption of aspirin and paracetamol, promotes nicotine dependence on tobacco and can enhance the action of drugs and plants with anticoagulant properties.
- Finally, caffeine can reduce the effectiveness of certain antacids (used to treat heartburn), alendronic acid (used to treat osteoporosis) and clozapine (used to treat psychosis).
- The tannins in tea can reduce the absorption of iron by the intestine. It's best to drink less than two liters of tea a day, away from meals or iron supplements.
- Pregnant and breast-feeding women should limit their caffeine intake to less than 200 mg a day, as it passes into the bloodstream of the foetus and into the milk. A higher intake has been associated with an increased frequency of miscarriages and low-birth-weight babies. What's more, caffeine increases the elimination of calcium and magnesium in the urine, which can lead to deficiencies.
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