Secondary Nutrient Deficiencies in Riboflavin Deficiency

Riboflavin deficiency is associated with hypochromic anemia as a result of secondary iron deficiency. The absorption of iron is impaired in riboflavin-deficient animals, with a greater proportion of a test dose retained in the intestinal mucosal cells bound to ferritin, and hence lost in the feces, rather than being absorbed. The mobilization of iron bound to ferritin, in either intestinal mucosal cells or the liver, for transfer to transferrin, requires oxidation of Fe + to Fe +, areaction catalyzed by NAD-riboflavinphosphateoxidoreductase (Powers et al., 1991 Powers, 1995 Williams et al., 1995). 

At least part of the impairment of iron absorption in riboflavin deficiency is a result of morphological changes in the intestinal mucosa, with hyperproliferation, an increased rate of enterocyte transit along the villi and a reduced number of (longer) villi and deeper crypts (Williams et al., 1996). 

In addition to the role of flavoproteins in iron metabolism, it is possible that the anemia associated with riboflavin deficiency is a consequence of the impairment of vitamin Be metabolism in riboflavin deficiency. Pyridoxine oxidase is a flavoprotein and, like glutathione reductase, is very sensitive to riboflavin depletion (McCormick, 1989). Vitamin Be deficiency can result in hypochromic anemia as a result of impaired porphyrin synthesis. Although riboflavin depletion decreases the oxidation of dietary vitamin Be to pyridoxal (Section 9.2), it is not clear to what extent there is secondary vitamin Be deficiency in riboflavin deficiency This is partly because vitamin Be nutritional status is commonly 

The disturbance of tryptophan metabolism in riboflavin deficiency, caused by impairment of kynurenine hydroxylase, can also result in reduced synthesis of NAD from tryptophan. This may therefore be a factor in the etiology of pellagra (Section 8.3.3.1). 

In species for which ascorbate is not a vitamin, riboflavin deficiency can also lead to considerably reduced synthesis and low tissue concentrations of ascorbate, since gulonolactone oxidase, the key enzyme in ascorbate synthesis (Section 13.2), is a flavoprotein. 

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