Selenium Compounds and Their Bioactivities: Molecular Mechanisms and Prospects for Functional Food and Therapeutic Applications

Selenium (Se) is an essential trace element for the human body and plays a vital role in various physiological processes. Plants serve not only as a major dietary source of selenium but also as natural biofactories capable of synthesizing a wide range of organic selenium compounds. The bioavailability and toxicity of selenium are highly dependent on its chemical form, which can exert varying effects on human physiology. Among these, organic selenium species exhibit higher bioavailability, lower toxicity, and greater structural diversity. In recent years, plant-derived selenium-containing compounds—selenium-enriched proteins, peptides, polysaccharides, polyphenols, and nanoselenium—have garnered increasing scientific attention. Through a systematic search of databases including PubMed, Web of Science, and Scopus, this review provides a comprehensive overview of selenium uptake and transformation in plants, selenium metabolism in humans, and the classification, composition, structural features, and biological activities of plant-derived selenium compounds, thereby providing a theoretical basis for future research on functional foods and nutritional interventions.