Vitamin B2 (Riboflavin)

Vitamin B2, known as riboflavin, is a water-soluble vitamin that functions primarily as a precursor for the co-enzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These co-enzymes are essential for red-ox reactions that generate cellular energy and support the metabolism of carbohydrates, fats, and proteins.

• Energy metabolism: Riboflavin-derived FMN/FAD are critical for the mitochondrial electron-transport chain, supporting ATP production and thereby enhancing physical stamina.
• Antioxidant protection: FAD-dependent glutathione reductase regenerates reduced glutathione, helping to neutralize reactive oxygen species and protect cellular membranes.
• Mucosal health: Adequate riboflavin maintains the integrity of oral, ocular, and dermal tissues, reducing the incidence of angular cheilitis and cataract progression.
• Neuro-cognitive support: Riboflavin contributes to the synthesis of neurotransmitters (e.g., serotonin) via its role in the kynurenine pathway, with epidemiological data linking higher intake to better cognitive performance in older adults.
• Migraine prophylaxis: Clinical trials have demonstrated that 400 mg/day of riboflavin reduces migraine frequency by ~40 % in susceptible individuals, likely through enhanced mitochondrial efficiency.

• Process: After absorption, riboflavin is phosphorylated by riboflavin kinase to form FMN, then further adenylated to FAD.
• Pathway: FMN and FAD serve as obligate co-enzymes for a broad set of flavoproteins, such as NADH-dehydrogenase (Complex I) and succinate-dehydrogenase (Complex II) in the mitochondrial respiratory chain. In the cytosol, they act as electron carriers in fatty-acid β-oxidation, the citric-acid cycle, and the synthesis of niacin (via the kynurenine pathway). FAD-dependent enzymes also catalyse the oxidation of vitamin C, metabolism of tryptophan, and regeneration of glutathione via glutathione reductase. By supporting these red-ox reactions, riboflavin sustains ATP production, maintains redox balance, and enables synthesis of other B-vitamins (e.g., niacin from tryptophan).

• Molecular Information: Riboflavin (C₁₇H₂₀N₄O₆; molecular weight ≈ 376.36 g·mol⁻¹) is a flavin-derived heterocycle consisting of an isoalloxazine ring fused to a ribitol side-chain.
• IUPAC Name: The IUPAC name is 7,8-dimethyl-10-[(2-hydroxyethyl)-10-hydroxy]-10-(1-hydroxy-2-pyridyl)-riboflavin (often shortened to “riboflavin”).
• Functional Groups: The isoalloxazine core provides the red-ox active site, while the ribityl moiety confers water-solubility.
• UV Absorption: The molecule exhibits two UV-absorbing peaks (≈ 360 nm and 450 nm) which are exploited in quantitative assays.
• Stability: Riboflavin is stable under neutral pH and light-protected conditions; exposure to UV or alkaline pH leads to degradation to lumichrome and other photoproducts, a key consideration for formulation stability.

• Natural Sources: Natural riboflavin is abundant in dairy (milk, cheese), egg whites, lean meats (especially liver), and green leafy vegetables (spinach, broccoli).
• Commercial Production: Commercially, riboflavin is produced primarily by fermentation of the filamentous fungus Ashbya gossypii or the bacterium Bacillus subtilis, which yield high-purity riboflavin (>99 %). Chemical synthesis (e.g., from ribose and 3,4-dimethyl-1,2-pyrrolidine) is also used, especially for large-scale food fortification.
• Supplement Considerations: For supplements, the source (fermentative vs. synthetic) is largely irrelevant to bioavailability, but regulatory agencies (FDA, EFSA) require that the final product be free of microbial contaminants and meet pharmacopeial standards for purity, potency, and absence of heavy metal residues. Proper packaging (opaque, airtight) preserves riboflavin stability and prevents photodegradation.