Bioactivity and Bioavailability of Tea (Camelia sinensis) and Its Possible Effect on Disease Prevention and Health...

Tea (Camellia sinensis) is a major dietary source of bioactive polyphenols, particularly catechins, which have been extensively investigated for their potential health-promoting properties. This narrative review provides a critical and integrative assessment of the current evidence, systematically differentiating mechanistic findings from preclinical and clinical data, with particular emphasis on bioavailability and translational relevance. While experimental studies consistently demonstrate strong biological activity under controlled conditions, clinical outcomes in humans remain heterogeneous and, in some cases, contradictory. Variability in dose, formulation, intervention duration, population characteristics, and the limited systemic availability of catechins appear to contribute substantially to these inconsistencies. By comparatively analyzing conventional and nano-enabled delivery strategies, this review highlights key factors of encapsulation efficiency, stability, release behavior, safety, and regulatory considerations that influence clinical application. The main contribution of this review lies in bridging mechanistic evidence with clinical translation, identifying methodological limitations across study types, and outlining critical research gaps that must be addressed to support evidence-based therapeutic or preventive applications of tea polyphenols.