Arterial stiffness, a major health issue, progresses with age. Dietary polyphenols improve vascular stiffening via vascular, inflammatory and other mechanisms, most likely due to their metabolites. Although promising effects for prevention and treatment of arterial stiffness have been reported for blueberry and olive polyphenols, it is largely unknown which polyphenol metabolites interact with which underlying mechanisms. In this project, polyphenol metabolites will be generated in gastrointestinal and liver simulations and will be identified subsequently. Since gut microbial composition is linked to arterial stiffness, is affected by polyphenols and is different in the elderly, an aged and young biotransformation model will be compared. Metabolites will be tested, separately and in mixtures analogous to the in vivo situation, in assays on vascular, oxidative, inflammatory and other mechanisms contributing to arterial stiffness. Also, polyphenol effects on gut microbial composition will be evaluated. This combination of analyses renders this project innovative and original. Results will provide a unique insight on polyphenol metabolism and the influence of age thereupon, and on polyphenol prebiotic-like effects. Moreover, they will increase understanding regarding the influence of olive and blueberry polyphenol metabolites on fundamental processes underlying arterial stiffness and multiple other pathological conditions, facilitating future research.