• Supports antioxidant defenses
        • Supports cellular energy production


B1 (riboflavin) is one of the water-soluble vitamins of the B complex, which plays an important role in cellular metabolism.


As the second B-complex vitamin to be discovered, riboflavin is also referred to as B2.

In addition to its critical role in preventing riboflavin deficiency disorders, it is on the WHO's List of Essential Medicines, the most effective and safe medicines needed in a health system.


The "flavin" part of its name comes from the Latin word meaning yellow (flavus) -- riboflavin supplements are bright yellow-orange in color, which is why they are yellow.

Yellow-colored urine may be noticed in persons who take large amounts of riboflavin.


Riboflavin takes two forms in the cell: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).


A number of vitamins are activated or metabolized by FMN and FAD, which are coenzymes required for cellular metabolism, ATP generation, and the metabolism of certain vitamins (folic acid, vitamin A, vitamin B3, and vitamin B6). [1–3]


Mitochondrial energy (ATP production)


  • Flavocoenzymes participate in redox reactions in numerous metabolic pathways critical for the metabolism of carbohydrates, lipids, and proteins[1]
  • Complex I (NADH dehydrogenase) of the electron transport chain requires FMN for its action[1,2]
  • Complex II (succinate dehydrogenase) of the electron transport chain requires FAD for its action[1,2]


NAD+ production


  • The kynurenine pathway requires FAD for the synthesis of the niacin-containing coenzymes NAD+ and NADP+ from tryptophan[4]


Vitamin metabolism


  • Flavoproteins are involved in the metabolism of several other vitamins (folate, vitamin A, vitamin B6, and niacin)[1]
  • FAD is required as a cofactor for the folate-metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR)[5]


Antioxidant defenses


  • Glutathione reductase requires FAD to regenerate two molecules of reduced glutathione from oxidized glutathione and protect against reactive oxygen species and oxidative stress[1,6,7]
  • Thioredoxin reductase requires FAD to reduce thioredoxin and support antioxidant defenses, redox signaling, and DNA synthesis and repair[6,7]
  • NADH peroxidase requires FAD to reduce hydrogen peroxide (H2O2)[7]


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[1] A. Saedisomeolia, M. Ashoori, Adv. Food Nutr. Res. 83, 57–81 (2018).
[2] J. M. Berg, J. L. Tymoczko, G. J. Gatto, L. Stryer, Eds., Biochemistry (W.H. Freeman and Company, 8th ed., 2015).
[3] S. O. Mansoorabadi, C. J. Thibodeaux, H.-W. Liu, J. Org. Chem. 72, 6329–6342 (2007).
[4] A. A.-B. Badawy, Int. J. Tryptophan Res. 10, 1178646917691938 (2017).
[5] C. Kutzbach, E. L. Stokstad, Biochim. Biophys. Acta. 250, 459–477 (1971).
[6] N. Couto, J. Wood, J. Barber, Free Radic. Biol. Med. 95, 27–42 (2016).
[7] R. L. Fagan, B. A. Palfey, in Comprehensive Natural Products II, H.-W. (ben) Liu, L. Mander, Eds. (Elsevier, Oxford, 2010), pp. 37–113.