The assessment of riboflavin status.

For the assessment of nutritional riboflavin status in man, several methods have been applied which are, in their basic principles, comparable with the methods for assessing the status of other vitamins. One approach involves the determination of the dietary riboflavin intake by means of food composition tables or by chemical analysis of food samples (Roine & Pekkharinen, 1968; van Schaik, 1968). These methods are, in general, laborious and expensive and are only available for use in connection with nutrition surveys or for studying the diet in certain institutions. Other methods for determining the riboflavin status are based on the estimation of either urinary riboflavin excretion, with or without a preceding riboflavin load, or of the riboflavin or FAD levels or both in blood or erythrocytes (see Pearson, 1967; Glatzle, Korner, Christellcr & Wiss, 1970). These procedures have certain disadvantages, since urinary riboflavin excretion may depend on the recent intake of the vitamin, on the nitrogen balance and on kidney function. Furthermore, riboflavin and FAD concentrations in blood or erythrocytes are difficult to measure very accurately, so that the results may be unreliable, especially when concentrations are very low, e.g. in people on a marginal vitamin intake. T o assess the riboflavin status as accurately as possible and by an easily applicable method, we became interested in looking for an cnzymic assay which depends on the biochemical or physiological function of riboflavin or its active forms in the body. We therefore investigated the NADPH,-dependent glutathione reductase (EC 1.6.4.2), which requires FAD as coenzyme, in erythrocytes of rats and human subjects and proposed this enzymic approach in the detection of riboflavin deficiency (Glatzle, Weber & Wiss, 1968). Similar procedures have subsequently been reported by Bamji (1969) and Beutler (1969) using the same enzyme but different assay conditions. The basis of the erythrocyte glutathione reductase (EGR) assay is similar to that of other enzymic functional tests, e.g. the transketolase activation test by Brin (1962) for evaluating the thiamin status and the glutamate-oxaloacetate aminotransferase activation assay by Raica & Sauberlich (1964) for the assessment of the pyridoxine status. During riboflavin deficiency, the activity of E G R is lowered, but it can be