Studies on prevention of obesity, metabolic syndrome, diabetes, cardiovascular diseases and cancer by tea

Abstract

Tea, a popular beverage made from leaves of the plant Camellia sinensis, has been studied extensively in recent decades for its beneficial health effects in the prevention of obesity, metabolic syndrome, diabetes, cancer, and other diseases. Whereas these beneficial effects have been convincingly demonstrated in most laboratory studies, results from human studies have not been consistent. Some studies demonstrated that weight reduction, alleviation of metabolic syndrome and risk reduction in diabetes were only observed in individuals who consume 3-4 cups of tea (600-900 mg tea catechins) or more daily. This chapter reviews some of these studies, the possible mechanisms of actions of tea constituents, and the challenges in extrapolating laboratory studies to human situations.

Keywords: Cancer; Diabetes; Metabolic syndrome; Obesity; Polyphenols.

Fig. 1

Structures of catechins and theaflavins.

Fig. 2

Proposal of action of tea constituents. The antioxidant activities of tea polyphenols contribute to the prevention of obesity, MetS, diabetes, CVDs and cancer. The binding of tea polyphenols to lipid and proteins in the intestine decreases macronutrient absorption. Caffeine also contributes to body weight reduction by increasing energy expenditure. These body weight lowering effects help to prevent related diseases. The binding of tea polyphenols to specific regulatory proteins and enzymes are also important mechanisms for alleviating metabolic abnormalities and preventing related diseases, including cancer. Caffeine may prevent cancer via specific mechanisms.