Advances on the Bioactivities, Safety, Preparation, and Applications of L-Se-Methyl-selenocysteine: Emphasis on Mechanistic Insights

As a critical public health threat, selenium inadequacy augments the risk of life-threatening disorders across multiple population subgroups. Conventional selenium supplements, classified chemically as inorganic salts or organic selenocompounds or physically as selenium nanoparticles based on particle size, are limited by suboptimal bioavailability, unresolved safety concerns, high production costs, and poor stability. L-Se-methyl-selenocysteine (L-Se-MSC), a distinct naturally occurring organoselenium, represents a promising alternative due to its superior stability, low toxicity, and versatile bioactivities. However, its mechanisms, safety, preparation methods, and applications in food, medicine, and agriculture have not yet been subjected to systematic and in-depth investigation to date. This review critically synthesizes recent advances in the aforementioned research pertaining to L-Se-MSC, based on the literature spanning from 2004 to 2025 and our laboratory findings. Evidence supports L-Se-MSC as a candidate for functional foods, biofortification, and pharmacological design, though further harmonization of analytical methodologies and well-designed confirmatory trials is still required.