Riboflavin
last authored: June 2010, Krista McLellan
last reviewed:
Introduction
Riboflavin, or vitamin B2, is a component of two coenzymes (FMN & FAD) that function in metabolism.
Daily Requirements
As Riboflavin is a water soluble vitamin, it cannot be stored in the body and must be ingested.
Daily requirements are as follows:
- 0-6 months: 0.3 mg
- 7-12 months: 0.4 mg
- 1-3 years: 0.5 mg
- 4-8 years: 0.6 mg
- 9-13 years: 0.9 mg
- males 14 and older: 1.3 mg
- females 14-18: 1.0 mg
- females 18 and older: 1.1 mg
- pregnant women: 1.4 mg
- breastfeeding women: 1.6 mg
Sources
Riboflavin can be found in the following foods:
- animal foodstuffs: milk products, eggs, meat (especially liver)
- enriched white bread/rolls/crackers
- mushrooms
- green leafy vegetables (spinach, broccoli, asparagus)
Digestion, Absorption, and Metabolism
Digestion: HCl in the stomach releases riboflavin from its bound form.
Absorption: occurs primarily through active transport or facilitated diffusion in the small intestine.
Metabolism: Riboflavin is converted into coenzyme forms FMN and FAD in most tissues, but primarily the small intestine, liver, heart, and kidney.
Transport: riboflavin is transported in the blood by protein carriers. A small amount is stored in the liver, kidneys, and heart. However, the nature of water soluble vitamins is that the excess amount is excreted in the urine. It casts a bright yellow hue to the urine when high amounts are excreted.
Biological Roles
The riboflavin coenzymes FMN & FAD function in redox reactions; they either take from or give substrates electrons in the form of hydrogen atoms. The riboflavin coenzymes are involved in many critical enzyme reactions of metabolism: passing hydrogens into the electron transport chain, participating in the breakdown of fatty acids (beta oxidation) to acetyl-CoA (the entry compound for the citric acid cycle), forming the vitamin b6 coenzyme, synthesizing tryptophan into niacin, and participating in folate metabolism and antioxidant defenses.
Deficiency
“Ariboflavinosis” (riboflavin deficiency) entails
- glossitis (inflammation of the tongue) and cheilosis (cracking of the skin around the mouth)
- seborrheic dermatitis (a disease of the sebaceous glands of the skin)
- stomatitis (inflammation of the mouth and throat)
- various nerve and eye disorders
- confusion and headaches.
Factors that may increase or worsen ariboflavinosis include: cancer, some forms of cardiovascular disease, and diabetes.
Alcoholics tend to be at an increased risk of ariboflavinosis due to the tendency to have a nutrient-deficient diet.
It should be noted that a lack of dietary riboflavin rarely occurs, and that sometimes ariboflavinosis is misattributed to a dysfunction in metabolic pathway disturbed by the deficiency of another necessary nutrient.
Overdose
An upper level of riboflavin does not appear to exist due to its rapid excretion of excess via urine.
Resources and References
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