IX. REQUIREMENTS 175 



than in ciisos of iU'cidoiital death. To what extent the lowered reserves arc 

 due to U)\v intake, defect ive al)sorpt ion and conversion, or increased destruc- 

 tion remains to he determined. 



c. Metabolic Injlucnccs 



During pregnancy and lactation there are increased requirements to 

 meet the metabolic needs of the mother and to provide for an adequate 

 transfer of vitamin A to the fetus and to the mother's milk. Artificial hy- 

 perthermia and febrile states in general reduce plasma levels of vitamin A, 

 owing to a variable degree to excessive utilization, inhibited release from 

 the liver and impaired absorption, causing at least a temporary increase in 

 requirements. Whether tocopherols can enhance liver storage of vitamin 

 A in man, as they have been shown to do in experimental animals, is not 

 known. They are reported as having little or no beneficial effect on the ab- 

 sorption of various forms of vitamin A in man.^^ There are suggestions that 

 sex differences in the utilization of vitamin A may exist in man,^^ a phenom- 

 enon which is quite marked in experimental animals.^* 



d. Kidney Dysfunctions 



There is evidence, recently summarized by Moore and Sharman,^'' that 

 vitamin A, which under normal conditions is not excreted by the human 

 kidney, appears in considerable amounts in the urine of patients with 

 chronic nephritis, pneumonia, and icterus. A somewhat antithetical situation 

 exists in the nephrotic syndrome in children, where serum vitamin A levels 

 are unusually high but there is no evidence of urinary loss.*^ Following 

 administration of test doses of vitamin A the serum levels show a marked 

 and sustained elevation. This is attributed to a failure of the liver to utiHze 

 or store vitamin A due to depletion of a liver protein component to which 

 vitamin A becomes attached. 



«» E. F. Week and F. J. Sevigne, J. Nutrition 40, 563 (1950). 



«« B. M. Kagan, E. M. Thomas, D. A. Jordan, and A. F. Abt, J. Clin. Invest. 29, 141 

 (1950). 



