Riboflavin, or vitamin B-2, was initially isolated from milk and its origin can be traced to English chemist Alexander Wynter Blyth in 1872;
it was originally called lactochrome or lactoflavin. Riboflavin is important for energy production, enzyme function, and normal fatty acid and amino acid synthesis. In addition to producing energy for the body, riboflavin works as an antioxidant and is necessary for the reproduction of glutathione, a free radical scavenger. Additionally, it is essential for normal development, growth, reproduction, lactation, physical performance, and well-being.
Riboflavin is water soluble and heat stable. Its chemical nomenclature is 7,8-dimethyl-10 (1′-D-ribityl) isoalloxazine.
Riboflavin is an essential component of coenzymes involved in multiple cellular metabolic pathways, including the energy-producing respiratory pathways. Flavoproteins are catalysts in a number of mitochondrial oxidative and reductive reactions and function as electron transporters. Riboflavin functions in several different enzyme systems. Two derivatives, riboflavin 5′ phosphate (flavin mononucleotide [FMN]) and riboflavin 5′ adenosine diphosphate (flavin adenine dinucleotide [FAD]), are the coenzymes that unite with specific apoenzyme proteins to form flavoprotein enzymes. Most of the flavin coenzyme systems help regulate cellular metabolism, whereas others are specifically involved in carbohydrate or amino acid metabolism systems. Riboflavin also appears to have a role in fat metabolism.
Riboflavin is not stored in large amounts; minute reserves are stored in the liver, kidneys, and heart. Riboflavin deficiency is usually associated with other vitamin B complex deficiencies; isolated riboflavin deficiency is rare.
Riboflavin deficiency is generally considered to be uncommon in the United States because of fortification of many foods, including grains and cereals.
Riboflavin in the diet
Milk and other dairy products make the greatest contributions of riboflavin in western diets. Other common dietary sources include the following:
Riboflavin deficiency can occur with a diet deficient in these riboflavin-rich foods. Additionally, glass milk containers promote degradation of the vitamin from exposure to light. Daily consumption of breakfast cereal and milk would be expected to provide an adequate intake of riboflavin.
The condition is more commonly seen in persons with such risk factors as pregnancy,
lactation, phototherapy for hyperbilirubinemia (in premature infants), advanced age,
low income, and/or depression.
Most dietary riboflavin is ingested as food protein.
In the stomach, gastric acidity cleaves most of the coenzyme forms of riboflavin (FAD and FMN) from the protein. The coenzymes are then hydrolyzed to riboflavin by pyrophosphatases and phosphatases in the upper intestine.
Primary absorption of riboflavin occurs in the proximal small intestine via a rapid, active and saturable transport system. The rate of absorption is proportional to intake, and it increases when riboflavin is ingested along with other foods and in the presence of bile salts. A small amount of riboflavin circulates via the enterohepatic system.
Malabsorption from conditions such as celiac disease, malignancies, and alcoholism can promote deficiency of riboflavin.
Riboflavin is transported in the bloodstream as a flavin-protein complex, which means that nonavailability of the carrier protein also leads to apparent riboflavin deficiency. Similarly, it is possible for antagonists to interfere with absorption and/or transport and thus create an apparent deficiency at receptor sites.