Vitamin B2: Riboflavin

Riboflavin, vitamin B2, is found in the human body as itself, flavin mononucleotide (FMN), or flavin adenine dinucleotide (FAD).¹ Riboflavin is destroyed by light but is relatively heat stable.¹ 

Absorption/Metabolism: FMN and FAD are absorbed using several transporters including RFVT1, RFVT2, and RFVT3.¹ The body does not absorb more than approximately 25 mg/day of riboflavin.¹ The heart, kidneys, and liver tissues contain a high concentration of riboflavin, and riboflavin found in brain tissue is regulated. Riboflavin has the ability to be converted into FMN and FAD, and FMN and FAD can also be converted into riboflavin.¹

Functions: Riboflavin serves as a coenzyme found within several nutrient metabolic pathways. Both FMN and FAD serve as electron acceptors during metabolism.¹ FMN is used as a coenzyme for NADH dehydrogenase found in the electron transport chain.¹ L-amino acid oxidase and lactate dehydrogenase also use FMN as a coenzyme during the interconversion of pyruvate and lactic acid.¹

FAD is used as a coenzyme for succinate dehydrogenase and cytochrome reductase used in the Krebs cycle and electron transport chain.¹

FAD also acts as a coenzyme for fatty acid oxidation and degradation of amino acids.¹

Dietary Reference Intake (DRI) - The recommended dietary allowance (RDA) for adult men and women over 19 years old is 1.3 and 1.1 milligrams/day.² 

Deficiency - Riboflavin deficiency presents with neurological and energy issues. Signs include cheilosis (cracked skin around mouth corners), glottis (inflamed tongue), and waxy skin appearance.¹

Toxicity - Uncommon as riboflavin is excreted in urine rapidly.¹ 

Dietary Sources of Riboflavin 

Riboflavin is found in a variety of foods including grains, fruits, and vegetables but is found highly among meat and dairy products. Riboflavin is enriched into refined grains after processing due to the loss of B vitamins, including thiamin. It is required by the U.S. government in a legislative act known as the Enrichment Act.¹ 

Meat -  beef liver, clams, salmon

Dairy -  eggs, milk, cheese 

Fruit/Vegetables - mushrooms, spinach, apples 

Starches - cereals, oats, bread 

Nuts/seeds - almonds, sunflower seeds

Source(s):

1. Denise M Medeiros and Robert E.C. Wildman, Advanced Human Nutrition, 4th ed. (Burlington, MA: Jones & Bartlett, 2019).

2. https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/