**Abstract**

Tea, next to water, is the beverage humans consume. Drinking the beverage tea is great for joining and collecting family members and public communities since ancient times. Tea plant *Camellia sinensis* has been cultivated for thousands of years, and its leaves have been used for medicinal purposes. Various studies suggest that polyphenolic compounds present in green and black tea are associated with beneficial effects in prevention of cardiovascular diseases, particularly of atherosclerosis and coronary heart disease. Anti-ageing, antidiabetic and many other health beneficial effects associated with tea consumption are described. Evidence is accumulating that catechins and theaflavins, which are the main polyphenolic compounds of green and black tea, respectively, are responsible for most of the physiological effects of tea. This review describes the evidence from clinical and epidemiological studies in the prevention of chronic diseases like cancer and cardiovascular diseases and inhibits pathogenic bacteria and general health promotion associated with tea consumption.

**Keywords:** green tea, black tea, health benefit, antibacterial activity

#### **1. Green tea**

Green tea is a popular drink, especially in Asian countries, although its popularity continues to spread across the globe. The health benefits of green tea, derived from the leaves of the *Camellia sinensis* [*Camellia sinensis* is a species of evergreen shrub or small tree whose leaves and leaf buds are used to produce tea. It is of the genus *Camellia* (Chinese: 茶花; pinyin: *cháhuā*, literally: "tea flower")] plant, have been studied for many years. Fairly recently, researchers have begun to look at the possibility of using green tea in antimicrobial therapy, and the potential prevention of infections. The particular properties of catechins found in the tea have shown promise for having antimicrobial effects. There are four main catechins (polyphenols) found in green tea: (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG). Three of these, ECG, EGC and EGCG have been shown to have antimicrobial effects against a variety of organisms [1, 2].

Among the health benefits that have been studied using green tea are: as an antioxidant, anti-inflammatory, anticarcinogenic, in cardiovascular health, oral health, and as an antimicrobial. Antioxidant effects come from the ability of green tea to limit the amount of free radicals by binding to reactive oxygen species (ROS) [3, 4]:

	- Green tea is an excellent source of powerful antioxidants, so it makes sense that it could reduce your risk of cancer, which it appears to do; **Breast cancer:** A meta-analysis of observational studies found that women who drank the most green tea had a 20–30% lower risk of developing breast cancer, the most common cancer in women [9].
	- **Prostate cancer:** One study found that men drinking green tea had a 48% lower risk of developing prostate cancer, which is the most common cancer in men [10].
	- **Colorectal cancer:** An analysis of 29 studies showed that those drinking green tea were up to 42% less likely to develop colorectal cancer [11]. Many observational studies have shown that green tea drinkers are less likely to develop several types of cancer. However, more high-quality research is needed to confirm these effects [12].
