Author(s): Emily J Thompson, Daniel R Collins and Sophia M Reynolds

Abstract: Chronic non-communicable diseases (NCDs) such as cardiovascular disease, type 2 diabetes, cancer and neurodegenerative disorders are major contributors to global morbidity, mortality and healthcare burden, with oxidative stress recognised as a key mechanistic link between these conditions and biological ageing. Phytochemicals bioactive secondary metabolites including polyphenols, carotenoids, terpenoids, alkaloids and organosulfur compounds have emerged as important dietary factors capable of modulating redox homeostasis, inflammation and metabolic function. This narrative, evidence-focused review synthesises mechanistic, observational and interventional data on the role of phytochemicals as natural antioxidants in the prevention of chronic diseases and the promotion of longevity. Relevant studies were identified through structured searches of major databases, focusing on work that quantified phytochemical or polyphenol intake, dietary phytochemical index scores or phytochemical-rich dietary patterns, and evaluated oxidative stress biomarkers, cardiometabolic risk factors, incident NCDs and mortality. Mechanistic and translational studies consistently demonstrate that phytochemicals exert both direct antioxidant effects (e.g. reactive oxygen species scavenging, metal chelation) and indirect actions via upregulation of endogenous antioxidant defences, attenuation of pro-inflammatory signalling and improvements in endothelial and mitochondrial function. Observational evidence indicates that higher intakes of phytochemical-rich foods and greater dietary polyphenol exposure are associated with more favourable oxidative and inflammatory profiles, modest but clinically relevant improvements in cardiometabolic risk factors, 15-30% lower risk of incident cardiovascular events and 10-30% reductions in all-cause and cardiovascular mortality. In contrast, large trials of high-dose isolated antioxidant supplements have produced largely null or inconsistent effects, highlighting the importance of whole-food matrices and phytochemical synergy. Taken together, the available evidence supports the concept that long-term consumption of diverse, phytochemical-rich plant foods represents a feasible and sustainable strategy to mitigate oxidative stress, reduce chronic disease burden and support healthy ageing and longevity, while underscoring the need for further high-quality trials to refine dose-response relationships and clarify inter-individual variability.

DOI: 10.22271/flora.2025.v13.i6a.1045