The impact of oolong and black tea polyphenols on human health

Tea (Camellia sinensis, Theaceae) is a popular beverage consumed worldwide. Green tea, oolong tea, and black tea are the three major tea types that are obtained through different levels of fermentation of the tea leaves. The health benefits of tea have been widely studied, and these effects are closely related to the structure and composition of polyphenols. In spite of growing evidences for health benefits of green tea, less research has been done using black and oolong teas, which are more widely consumed. This mini-review mainly focused on biological activities of oolong and black tea, and their characteristic polyphenols, i.e., oolong tea theasinensins, and black tea theaflavins. Several biological activities have been associated with tea consumption and polyphenol contents, including anticancer activities, antioxidant activities, anti-cardiovascular activities, antimicrobial activities, anti-hyperglycemic activities, and anti-obesity activities, suggesting the important roles of tea and tea polyphenols in human health and in disease prevention and treatment. However, application of tea polyphenols in the development of dietary interventions or alternative treatment approaches need to be aware of the low bioavailability and potential toxicity of tea polyphenols. Future studies to incorporate existing methods or develop new methods for enhancing polyphenol absorption will help to obtain these health benefits with a lower dose and prevent overdose toxicity.