Vitamin B2, or riboflavin, is a water-soluble vitamin. It functions primarily as a coenzyme for many metabolic processes in the body, such as red blood cell formation and nervous system function. Riboflavin is involved in energy production as part of the electron transport chain that produces cellular energy. As a building block for flavin adenine dinucleotide (FAD), riboflavin is a crucial component in converting food into energy. FAD is required for electron transport and ATP production in the Krebs cycle. FAD is also the cofactor for methylenetetrahydrofolate reductase, the enzyme that catalyzes the formation of 5-methyltetrahy-drofolate and acts as a methyl donor for homocysteine remethylation. Through this methylation pathway, riboflavin supplementation, together with folate, may act to reduce plasma levels of homocysteine.

Liver, dairy products, dark green vegetables, and many seafoods are good sources of riboflavin. Dietary supplements containing riboflavin, in addition to being marketed as general nutrients, will frequently contain claims for increased energy levels, treatment of chronic fatigue, improved concentration and mood, reduced plasma homocysteine, and promotion of heart health.

The term B complex simply refers to a mixture or combination of the eight essential B vitamins: thiamin (B, riboflavin (B2), niacin (B3), pyridoxine (B6), pantothenic acid, folic acid, cyanocobalamin (B2)- and biotin. Most of the B vitamins play a critical role as cofactors in cellular energy metabolism. Cofactors can be thought of as “helper nutrients” that assist chemical reactions. For example, the process of glycolysis, which converts energy stored as glycogen into glucose molecules, requires vitamin B(l and biotin. The conversion of pyruvate (a metabolite of glucose) to acetyl coenzyme A (the first step in the Krebs cycle in energy metabolism) requires pantothenic acid, and further metabolism requires biotin, riboflavin, and niacin. Lack of any of the B vitamins can cause fatigue and lethargy, which is why B-complex supplements are often promoted as “energy boosters” and “stress formulas.”

Virtually every multivitamin/mineral supplement available contains the full complement of B-complex vitamins at RDA or higher levels. It is often a better value to get B vitamins through a multivitamin supplement than as a separate B-complex supplement. This chapter on energy supplements contains information on vitamins BI and B2, while other B vitamins, such as niacin, folic acid, BG, and El2l are covered in the “B-Complex Vitamins (B, B12, Folic Acid, Niacin.

Requirements for riboflavin, like most B vitamins, are related to calorie intake; therefore, the more food consumed, the more riboflavin needed to support the metabolic processes that convert food into usable energy. Women should be aware that riboflavin needs are elevated during pregnancy and lactation as well as by the use of oral contraceptives (birth control pills). Athletes may require more riboflavin because of both increased caloric intake and increased needs of exercise.

In cases of subclinical (biochemically defined) riboflavin deficiency, daily supplementation of diets with riboflavin (with or without other B vitamins) resulted in an increase in physical work capacity (Suboticanec etal., 1990). In other studies, adding riboflavin to an antianemia regimen (dietary changes plus ferrous sulphate) resulted in a significant increase in circulating plasma iron and in iron stores (hemoglobin) compared with iron supplements alone (Powers et al., 1987). As expected, riboflavin supplements have no effect on physical performance when added to a riboflavin-adequate diet (Manore, 2000).

There is no strong support for the efficacy of isolated riboflavin supplements in promoting health besides correcting a nutrient deficiency. Despite the role of riboflavin in a variety of energy-generating processes, the role for a supplement in directly improving energy levels in a well-nourished person is unlikely.

Isolated riboflavin supplements are not necessary. Virtually all multivitamins and B-complex formulas contain riboflavin at RDA or higher levels. When it comes to supplementing with B-complex vitamins, isolated single-vitamin supplements are not recommended. A more balanced approach is to supplement with the entire B-complex spectrum simultaneously or at least with several of the B vitamins in the same supplement. High-dose supplementation with any single B-complex vitamin can interfere with the absorption of another. For example, a folic acid supplement of 400 ug/day (a common level) has been shown to exacerbate a riboflavin deficiency and elevate plasma homocysteine levels (Moat et al., 2003). Likewise, studies of combined B-vitamin supplementation (folate plus B6 plus riboflavin) generally show that this approach has a more pronounced effect on metabolic parameters, such as plasma homocyst-eine levels, than supplementing with any single B vitamin (Jacques et al., 2001).

No serious side effects have been reported for supplementation with riboflavin at levels several times above the DV of 1.7 mg. Because the body excretes excess riboflavin in the urine, high supplemental levels are likely to result in brightly colored urine (fluorescent yellow).

The DV for riboflavin is 1.7 mg (RDA is 1.3 mg/day for men, 1.1 mg/ day for women). The Food and Nutrition Board sets no LJL intake of riboflavin, but as much as 200 mg/day of riboflavin is considered safe (the NOAIiL set by the Council for Responsible Nutrition).

When it comes to defining optimal amounts of vitamins and minerals, confusion is more the rule than the exception. Before 1 997, the benchmark of nutritional adequacy was the RDA established by the FNB. In general, the RDAs have always been viewed (as judged by the I’NB) “to be adequate to meet the known nutrient needs of practically all healthy persons.” Because scientific knowledge regarding the roles of nutrients, and their role in health and disease, has expanded dramatically since the inception of the RDAs, a new set of terminology ((he DRIs) has been established. The DRIs are based on contemporary scientific studies related to the role of nutrients in reducing the risk of osteoporosis, cancer, cardiovascular disease and other chronic conditions. DRl is a generic term used to refer to the following reference values:

Estimated average requirement (EAR): the intake value that meets the nutrient requirements of 50% of an age- and gender-specific population.

Recommended dietary allowance (RDA): the intake value that meets the nutrient requirements of nearly all people in an age- and gender-specific group.

Upper intake (UL): maximum intake of a specific nutrient that is unlikely to pose health risks.

Adequate intake (AI): suggested levels of nutrient intake that are established when insufficient data exist to establish a true RDA.

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