Riboflavin status

Two methods of assessing riboflavin status are generally used urinary excretion of the vitamin and its metabolites, and activation of EGR. Criteria of riboflavin adequacy are shown in Table 7.5. 

Glutathione reductase is especially sensitive to riboflavin depletion, in deficient animals, the activity of glutathione reductase responds earlier and more markedly than any other index of riboflavin stams apart from liver concentrations of flavin coenzymes and the activity of hepatic flavokinase (Prentice and Bates, 1981a, 1981b). The activity of the enzyme in erythrocytes can therefore be used as an index of riboflavin status. 

There is some evidence that riboflavin status affects the stability of the thermolab ile variant of methylene tetrahydrofolate reductase (Section 10.3.2.1), and that supplements of riboflavin may lower plasma homocysteine (Section 10.3.4.2) in people who are homozygous for the variant enzyme (McNulty et al., 2002). 

McNulty H, McKinley MC, Wilson B, McPartlin J, Strain JJ, Weir DG, and Scott JM (2002) Impaired functioning ofthermolabile methylenetetrahydrofolate reductase is dependent on riboflavin status implications for riboflavin requirements. American Journal of Clinical Nutrition 76,436-41. 

Prentice AM and Bates CJ (1981a) A biochemical evaluation of the erythrocyte glutathione reductase (EC 1.6.4.2) test for riboflavin status. 1. Rate and specificity of response in acute deficiency. British Journal of Nutrition 45,37-52. 

Flavins are lost from the body as intael riboflavin, rather than as a breakdown product of riboflavin. Hence, vitamin status may be assessed by measuring the level of urinary riboflavin. Generally, the loss of 30 ig of riboflavin/g creatinine or less per day indicates a deficiency. This metht>d of assessment is not preferred because it is influenced by a number of factors unrelated to vitamin status. Another problem with this method is its great sensitivity to a short-term deficiency thus, it does not necessarily reflect the true concentrations of FAD and FMN in tissues. The most reliable way to assess riboflavin status is by a functional test. The test involves the assay of glutathione reductase, using red blood cells as the source of... 

Saubcriich, H. E., Judd, J. H., Nichoalds, C. F.., Broquist, H. P, and Darby, W. J, (1972). Application of the erythrocyte glutathione reductase assay in evaluating riboflavin status in a high school student population. Am. /. Cfjri. Nutr, 25, 756-762. 

Btodtem try Riboflavin Riboflavin Deficiency A e m t of Riboflavin Status Pantottienic Add... 

Riboflavin status is assessed by (1) determination of urine riboflavin excretion, (2) a functional assay using the activation coefficient of stimulation of the enzyme glutathione reductase by FAD, or (3) direct measurement of riboflavin or its metabolites in plasma or erythrocytes. The advantages and disadvantages of functional or direct methods have been discussed in the section on thiamine. 

Direct measurement of riboflavin, FMN, and FAD in plasma or erythrocytes may be made by HPLC, usually with fluorescence detection after protein precipitation or by capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). In a study of riboflavin status and FMN and FAD concentrations in plasma and erythrocytes from elderly subjects at baseline and after low-dose riboflavin supplementation, using both activation coefficient measurements and CE-LIF, it was concluded that concentrations of aU Ba vitamers except plasma FAD are potential... 

Moat SJ, Ashfield-Watt PA, Powers HJ, Newcombe RG, McDoweE IF. Effect of riboflavin status on the homocysteine-lowering effect of folate in relation to the MTHFR (C677T) genotype. Clin Chem 2003 49 295-302. 

Use of oral contraceptives may increase the dietary requirement for riboflavin. Riboflavin status can be evaluated from the activity of erythrocyte glutathione reductase, an FAD-requiring enzyme, before and after addition of exogenous FAD. A low initial activity or a marked stimulation by FAD (or both) is indicative of ariboflavi-nosis. 

An example of the difference between the AI and the EAR is provided by riboflavin. Very few data exist on the nutrient requirements of very young infants. However, human milk is the sole recommended food for the first 4 to 6 months, so the AI of the vitamin riboflavin for this life stage group is based on the amount in breast milk consumed by healthy full-term infants. Conversely, the riboflavin EAR for adults is based on a number of studies in humans relating dietary intake of riboflavin to biochemical markers of riboflavin status and development of clinical deficiency symptoms. 

The clinical implications of a low riboflavin status in patients on AEDs are largely unknown. There may be an inhibitory effect on C677T MTHFR function and homocysteine metabolism. Importantly, riboflavin deficiency may be related to the elevated risk of foetal malformations in women on AEDs. 

Glutathione reductase has selenium at the catalytic site, as a selenocysteine residue (section 11.15.2.5) this explains the role of selenium as an antioxidant nutrient. Glutathione reductase is a flavoprotein, and is especially sensitive to riboflavin (vitamin B ) depletion as discussed in section 11.7.4.1, measurement of glutathione reductase is used as a means of assessing riboflavin status. 

The main dietary sources of riboflavin are milk and dairy products, which provide 25% or more of the total intake in most diets, and it is noteworthy that average riboflavin status in different countries reflects milk consumption to a considerable extent. In addition, because of its intense yellow colour, riboflavin is widely used as a food colour. 

Glutathione reductase is especially sensitive to riboflavin depletion, and the usual way of assessing riboflavin status is by measurement of the activation of red blood cell glutathione reductase by FAD added vitro (section 11.6.4.1). An activation coefficient > 1.7 indicates deficiency. 

In Western countries a clear indication for vitamin Bj treatment is rare at the moment. When newborn infants are given 0.5 mg FMN/day during phototherapy, a decrease in riboflavin status can be avoided (19). FMN and FAD are cofactors for complex I and II in the respiratory chain. In some cases of respiratory chain encephalomyopathy, high doses of riboflavin resulted in clear clinical improvement (22). 

The enzyme can be measured in red blood cells to assess the riboflavin status of the body. Riboflavin is a component of the FAD coenzyme. When the body s riboflavin status is good, the enzyme is saturated with FAD and addition of exogenous FAD to the assay mixture will result in little or no increase in activity. On the other hand, if there is inadquate riboflavin intake, addition of FAD causes a marked activation of the enzyme. 

Riboflavin can be measured by microbiological or fluorimetric methods. The erythrocyte enzyme, glutathione reductase, requires FAD as a cofactor and its measurement in the presence and absence of added FAD is therefore considered a good indicator of riboflavin status. 

Blanck, H.M., Bowman, B.A., et al. (2002) Angular stomatitis and riboflavin status among adolescent Bhutanese refugees living in southeastern Nepal. Am J Clin Nutr 76,430-435. 

LeBlanc, J.G., Burgess, C, Sesma, F., et al. (2005a) Lactococcus lactis is capable of improving the riboflavin status in deficient rats. Brit J Nutr 94,... 

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