The impact of (poly)phenol-rich foods and extracts on flow-mediated dilation (FMD): a narrative review

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality worldwide, with endothelial dysfunction as a key precursor. Flow-mediated dilation (FMD), the gold-standard measure of endothelial function, is improved by (poly)phenol-rich foods and extracts, with increases of 1% FMD representing 13% reduced cardiovascular risk. This narrative review aims to evaluate the efficacy of various (poly)phenol-rich foods and extracts on endothelial function as measured by flow-mediated dilation (FMD) and assesses the feasibility of a food-first approach. Literature was systematically searched from databases including PubMed and Web of Science, focusing on human clinical trials. While all (poly)phenol-rich food groups demonstrate variable effects, berries (0.9-2.6%), cocoa (0.7-5.9%), and tea (1.2-4.8%) have the most robust evidence, consistently improving FMD, with chronic intake sustaining benefits. A large variance (0.8-8.7%) was observed with grape-derived (poly)phenols, making their effects difficult to substantiate without detailed compositional or metabolomic data; however, a few key studies highlight their potential. Citrus polyphenols also exhibit variable FMD responses (0.2-7.2%). However, strong mechanistic evidence supports their role in vascular health and nitric oxide (NO) bioavailability. Coffee exhibits a variable response, initially impairing FMD, likely due to caffeine, before later improving endothelial function as phenolic metabolites increase. Although estimated (poly)phenol intake in Western populations is high (∼1000-1200 mg day^-1), it is primarily derived from tea, coffee, and cocoa, limiting exposure to diverse bioactive compounds. Moreover, the food matrix significantly influences bioavailability, with co-consumed components such as milk or sugar attenuating FMD responses. Interestingly, fortification and enrichment maintain bioactivity and may optimize intake, ensuring consistent and diverse delivery. Future research should refine dietary guidelines, establish intake thresholds, and explore fortification strategies to maximize cardiovascular benefits while considering dose-response relationships and long-term efficacy.