From Biosynthesis to Legislation: A Review of Hydroxytyrosol's Biological Functions and Safety.

Hydroxytyrosol (HT), a potent phenolic compound derived from olives, has attracted significant attention due to its exceptional antioxidant, anti-inflammatory, and antimicrobial properties. This review comprehensively examines recent advances in the synthesis, biological functions, safety profiles, and legal regulations of HT. We discuss both natural and biotechnological synthesis routes, including enzyme-mediated, non-transgenic, and transgenic biosynthetic methods, highlighting recent innovations that have improved yield and purity. The review further explores the multifaceted biological activities of HT, ranging from its role in cardiovascular protection and neuroprotection to its anticancer and metabolic regulatory effects. Safety assessments from animal and human studies are analyzed, demonstrating low toxicity and favorable metabolic profiles at physiologically relevant doses. Additionally, we compare international regulatory frameworks from the United States, China, and the European Union, which underscore the compound's safe use in food, pharmaceuticals, and cosmetics. Finally, the review outlines future research directions aimed at optimizing production methods, enhancing bioavailability, and addressing long-term toxicological outcomes, thereby reinforcing HT's potential as a high-value functional ingredient in various industries.