Tea, the Most Popular Beverage Worldwide, is Beneficial to Human Health. Studies on antioxidant polyphenolic constituents and epidemiological evidence for disease prevention

Abstract Tea is the most consumed beverage globally following only fresh water. International statistical data showed that global tea production amounted to 5.7 million metric tons in 2016. The countries leading the top list for tea production are China, India, Kenya, Sri Lanka, and Indonesia. Tea (Camellia sinensis) is cultivated for many centuries in more than 30 countries. Research showed that people have been consuming brewed tea for almost 4,000 years. In the last decades many research investigations focused on the health benefits of tea on a number of chronic diseases. Clinical and epidemiological studies and experimental investigations in animals supported evidenve that tea can reduce the risk of cardiovascular diseases (CVDs), some forms of cancer, type 2 diabetes and neurodegenerative diseases. Also, tea consumption can have beneficial influence on oral health (fluoride from tea has reduced dental caries) and is effective for stomach pains and other physiological functions such as anti-hypertensive effect, body weight control, antibacterial and antiviral effects. Tea leaves contain over 2,000 components, such as polyphenols (flavonoids, etc), carotenoids, alkaloids (caffeine, theophylline, theobromine), lignans, amino acids (including L-theanine), vitamins, minerals and trace elements. The majority of these compounds have strong antioxidant activity and can scavenge reactive free radicals, reduce oxidative stress and modulate inflammatory processes. Most studies showed that drinking tea (black, green, oolong, etc) habitualy can help prevent lifestyle‐related diseases, such CVDs, various types of cancer and type 2 diebetes. Tea and health outcomes have been the subject of numerous animal studies, and human epidemiological and clinical studies in the last decades. Despite the inconsistent results of human studies, scientists have enlarged their epidemiological studies investigating the strong antioxidant activity of tea catechins and their health benefits. In particular, mechanisms of reduction of oxidative stress, inflammation and other epigenetic modifications when daily consumption increased more than 4 cups per day in adults..