Diet & Nutrition – Vitamin B2, Riboflavin

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Vitamin B2 is more commonly known as riboflavin. Riboflavin is a water-soluble vitamin, meaning that same amounts are stored in the liver and kidney but are not stored freely in the body, which is why it needs to be replaced frequently. Riboflavin is easily destroyed by UV light and radiation therefore foods with this vitamin need to be handled carefully.

Riboflavin was initially characterized by E.V. McCollum at the University of Wisconsin. The 3 forms include: Riboflavin-absorption form FMN-flavin mononucleotide FAD-flavin adenine dinucleotide

The active compound: Flavokinase: riboflavin + ATP FMN + ADP

Flavin synthetase: FMN + ATP FAD + Ppi

Flavokinase expression is enhanced by thyroid hormone, adrenocorticotropic hormone (ACTH) and aldosterone.

Functions Riboflavin is part of a coenzyme that facilitates in the release of energy from nutrients in the body. Riboflavin also supports normal vision and skin health.

Coenzymes FMN and FAD are cofactors in numerous oxidation/ reduction reactions. They are donors and receptors of 2 protons. They are essential for generating energy during metabolism of beta-oxidation and the TCA cycle. Examples:

TCA Cycle: succinate + FAD fumarate + FADH2

Fatty acid oxdiation (1st step):

palmitate (16:0) + FAD palmitic (16:1) + FADH2

Deficiency Deficiencies with riboflavin are rare; it usually will occur, though, with other nutrient deficiencies. Symptoms of riboflavin deficiency include: o cheilosis (cracking at the corners of the mouth) o alopecia (hair loss) o a purple-reddish-inflamed tongue, red and/or swollen mouth cavity o angular stomatitis o eczema and dermatitis o conjunctivitis (inflammation of the muscus and lining of the eye) o cornea vascularization o severe ophthalmia o peripheral nerve dysfunction.

Some predisposing conditions that may lead to a riboflavin deficiency including the inborn error of a deficiency of D-glucose-6-phosphate dehydrogenase. This inborn error does not allow the body to add a phosphate group onto the riboflavin molecule to produce FMN. Other conditions include beta-thalassemia and kidney dialysis. The use of chlorpromazine and antimalarials compete with absorption while hyperthyroidism drugs depress the flavokinase enzyme. Oral contraceptives (high estrogen) often elevate and deplete circulating riboflavin levels. Also, diabetes, malignancy, congestive heart failure, alcoholism, chronic stress, and trauma may cause a predisposition to a riboflavin deficiency.

Sources Animal origin-based foods like liver, eggs, and pork have the most readily available sources to be absorbed. Other rich sources include milk sources like 2% milk, yogurt, ice milk, and cottage cheese. Fruits, vegetables, and cereal grains are a minor contributor of this vitamin.