Vitamin B2

Overview

Riboflavin is essential for normal growth and development, reproduction, lactation, physical performance, and well-being. It participates in essential biochemical reactions, especially those that yield energy. Vitamin B₂ is water-soluble and, like other B vitamins, it is not appreciably stored and must be supplied daily. Riboflavin belongs to a group of yellow fluorescent pigments called flavins. In its pure state, it is a yellow crystalline powder with a slight odor. When excreted, it gives the urine a characteristic bright yellow color.

Riboflavin combines with phosphoric acid to become part of two important flavin co-enzymes, FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide). FMN and FAD are known to bind to over 100 flavoprotein enzymes. These riboflavin-containing enzymes, which function as hydrogen carriers, catalyze many of the oxidation-reduction reactions in cells. (1)

Dosage Info

Dosage Range

1.2-100mg daily. Occasionally higher doses, up to 400mg per day, have reportedly been used under medical supervision for certain conditions such as migraine headaches. (2)

Most Common Dosage

10mg daily.

Dosage Forms

Tablets, capsules, liquids, liposomal sprays, and effervescent tablets.

Adult RDI

1.7mg

Adult ODA

6-15mg

RDA

• Infants < 6 months: 0.3mg (Adequate Intake, AI)
• Infants 7-12 months: 0.4mg (AI)
• Children 1-3 years: 0.5mg
• Children 4-8 years: 0.6mg
• Children 9-13 years: 0.9mg
• Males >14 years: 1.3mg
• Females 14-18 years: 1.0mg
• Females >19 years: 1.1mg
• Pregnancy: 1.4mg
• Lactation: 1.6mg

Interactions and Depletions

Interactions

• Tricyclic antidepressants

Depletions

• Antibiotics
• Oral contraceptives
• Phenothiazines

Active Forms

Riboflavin, riboflavin hydrochloride, and activated riboflavin, which is riboflavin-5-phosphate

Absorption

Vitamin B₂ is absorbed from the upper part of the small intestine, and better absorbed when taken with food. Only approximately 15 percent is absorbed if taken alone versus 60 percent absorption when it is taken with food. The conversion of riboflavin into its coenzymes takes place in most cells throughout the body, but especially in the cells of the small intestine, liver, heart, and kidney.

Toxicities & Precautions

General

There are no known toxicities associated with riboflavin.

Functions in the Body

Fatty Acids/Amino Acids/Pyruvic Acids

Riboflavin-containing coenzymes (FMN and FAD) play roles in fatty acid synthesis, beta-oxidation of fatty acids, deamination of amino acids, and conversion of pyruvic acid to acetyl coenzyme A.

Energy Production

Plays a role in the conversion of carbohydrates to ATP in the production of energy.

Antioxidant Activity

Antioxidant activity, both by itself, and as part of the enzyme glutathione reductase.

Growth

Necessary for growth and reproduction and the healthy growth of skin, hair, and nails.

Clinical Applications

Cataracts

Riboflavin is part of glutathione reductase, which is an important enzyme that helps provide antioxidant protection in the eyes. (3)

Migraines

Riboflavin has been successful in both the prevention and treatment of migraines. (4)

Depression

Riboflavin is one of the B vitamins found to be deficient in psychiatric patients. (5)

Symptoms and Causes of Deficiency

Vitamin B₂ deficiencies primarily affect the skin, eyes, and mucous membranes of the GI tract. Deficiencies seldom occur alone, but rather as a component of multiple-nutrient deficiencies.

Cheilosis, which is a classical sign of riboflavin deficiency, is characterized by cracks in the corners of the mouth, soreness and burning of the lips, mouth, and tongue, glossitis (magenta-colored tongue), and inflamed mucous membranes. Riboflavin deficiency can also affect the eyes, causing reddening, tearing, burning and itching, as well as eyes that tire easily and become very sensitive to light. Other symptoms that can develop include dry, itchy, scaly skin (seborrheic dermatitis) and scaling eczema of the face and genitals. In severe long-term deficiency, damage to nerve tissue can cause depression and hysteria. (6)

Riboflavin is heat stable, but very sensitive to destruction by light. Because it is water soluble, substantial amounts are lost by leaching into water when cooking. Since the vitamin exists in the germ and bran of grains, milling and processing of grains results in substantial losses.

A U.S. Department of Agriculture survey estimated that 34 percent of Americans get less than the RDA of vitamin B₂ daily. (7) Individuals at greatest risk for riboflavin deficiency include alcoholics, (8) the elderly, (9) and prematurely born infants. (10)

Women taking oral contraceptives have an increased need for vitamin B₂, (11) and chlorpromazine, (12) and tricyclic antidepressants (13) also inhibit the absorption of riboflavin and can cause nutrient depletions.

The thyroid hormone levothyroxine regulates the enzyme flavin kinase, which is necessary for the synthesis of the FAD-containing enzyme erythrocyte glutathione reductase (EGR). This means that individuals with hypothyroidism are likely to have what amounts to a riboflavin deficiency, which can be corrected with levothyroxine therapy. (14)

Dietary Sources

The best sources of vitamin B₂ are liver, milk, and dairy products. Moderate sources include meats, dark green vegetables, eggs, avocados, oysters, mushrooms, and fish (especially salmon and tuna).

References

1. Reed PB. Nutrition: An Applied Science. New York: West Publishing Company; 1980:247-48.
2. View Abstract: Schoenen J, Jacquy J, Lenaerts M. Effectiveness of high-dose riboflavin in migraine prophylaxis. Neurology. Feb1998;50(2):466-470.
3. View Abstract: Leske MC, et al. Biochemical Factors in the Lens Opacities. Case-control Study. The Lens Opacities Case-Control Study Group. Arch Ophthalmol. Sep1995;113(9):1113-19.
4. View Abstract: Schoenen J, et al. Effectiveness of High-dose Riboflavin in Migraine Prophylaxis. A Randomized Controlled Trial. Neurology. Feb1998;50(2):466-70.
5. View Abstract: Carney MW, et al. Thiamine, Riboflavin and Pyridoxine Deficiency in Psychiatric In-patients. Br J Psychiatry. Sep1982;141:271-72.
6. Wilson JA, Petersdorf RG, et al, eds. Disorders of Vitamins-deficiency, Excess and Errors of Metabolism. Harrison’s Principles of Internal Medicine. 10th ed. New York: McGraw-Hill; 1978.
7. Pao EM, Mickle SJ. Problem Nutrients in the United States. Food Technology. 1981;35:58-62.
8. Hell D, et al. Vitamin B1, B2 and B6 Status in Chronic Alcoholics. Nutr Metab. 1977;21(1):134-5.
9. View Abstract: Zheng JJ, et al. What is the Nutritional Status of the Elderly? Geriatrics. Jun1989;44(6):57-58, 60, 63-64.
10. View Abstract: Sisson TR. Photodegradation of Riboflavin in Neonates. Fed Proc. Apr1987;46(5):1883-85.
11. View Abstract: Webb JL. Nutritional Effects of Oral Contraceptive Use: A Review. J Reprod Med. Oct1980;25(4):150-56.
12. View Abstract: Pelliccione N, et al. Accelerated Development of Riboflavin Deficiency by Treatment with Chlorpromazine. Biochem Pharmacol. Oct1983;32(19):2949-53.
13. Pinto J, et al. Inhibition of Riboflavin Metabolism in Rat Tissues by Chlorpromazine, Imipramine, and Amitriptyline. J Clin Invest. May1981;(67(5):1500-06.
14. View Abstract: Cimino JA, et al. Riboflavin Metabolism in the Hypothyroid Newborn. Am J Clin Nutr. Mar1988;47(3):481-83.