Day: September 24, 2021

Tea has been used as a refreshing drink for centuries. Tea is said to have health benefits – does the latest scientific evidence support this? Is tea a healthy source of hydration?   History and types of tea Tea is a beverage, which has been consumed for centuries. It is the most-widely consumed drink in the world, after water.1 Figure 1 shows tea consumption per capita in some European countries. Figure 1: Tea consumption per capita in Europe2 Tea is produced by adding hot water to the leaves from the tea plant, Camellia sinensis. This process is called infusion. Herbal or fruit teas, despite their name, are not strictly teas as they come from other plant species (for example, lime tree or chamomile). Different processing methods are used to produce the hundreds of varieties of tea: Black teas, which are most common in Europe3, are produced when tea leaves are fermented (broken down by the enzymes in the tea leaves, in a temperature controlled room) and then dried. These processes release the specific polyphenols, which produce the distinctive colour and flavour.4 Green (unfermented) tea is produced by steaming, before drying, to minimise oxidation by enzymes – keeping the colour of the leaf, and giving its flavour characteristics. Oolong tea is somewhere between green and black tea in terms of fermentation and taste – its leaves are only partially oxidised. Black and green (and oolong) teas contain different types of polyphenols, but the total polyphenol content is similar.5 Tea can be drunk as a simple infusion, or may have added milk or lemon, or sugar. However, more research is needed to understand to what degree and through which mechanisms this affects the bioavailability of the different polyphenols. Is tea good for health? There is much more research published on green tea than black (and other) teas. A recent exhaustive review looking into associations between food and beverage groups and diet-related chronic diseases, reported that tea was the most protective of all of the commonly consumed beverages; people reporting the highest intake of tea was associated with significantly reduced risk of type 2 diabetes (by 16%), cardiovascular disease (by 28%) and cancers (by 34%), although other studies have not shown clear relationships between tea and cancers.6 Another large study reported each additional daily cup of tea resulted in an associated 9% lower all-cause mortality.7 Many of the proposed benefits have been attributed to the presence of specific polyphenols called flavonoids having a beneficial effect on blood vessels, due to their antioxidant and anti-inflammatory properties, but caffeine and fluoride […]