174 vitamins a and carotenes 



4. Features Influencing Requirements 



The factors which may modify individual needs for vitamin A fall gen- 

 erally into three categories. First, conditions which interfere with the nor- 

 mal absorption of vitamin A and with the absorption and intestinal con- 

 version of carotene to vitamin A. Second, types of liver injury which alter 

 the capacity of the liver to store or to regulate the release of vitamin A. 

 Third, changes in the general metabolism of the individual which result in 

 excessive utilization or excretion of vitamin A reserves. 



a. Factors Interfering with Absorption 



Inadequacy of pancreatic lipase for hydrolysis of vitamin A esters and 

 of bile salts, and conditions which alter the normal function and structure 

 of the small intestine, seriously impair the absorption of vitamin A and 

 carotene. For these reasons, requirements for vitamin A are increased in 

 premature infants, and in disease states such as pancreatic fibrosis, celiac 

 disease, sprue, infectious hepatitis, congenital obstruction of the bile ducts, 

 giardiasis, prolonged diarrhea, colitis, and generalized infections. "-^^ There 

 is evidence of diminished intestinal absorption of vitamin A and carotene 

 in elderly individuals.*^ The presence of mineral oil interferes with the ab- 

 sorption of carotene, and to a lesser extent with the absorption of vitamin 

 A. Although symptoms of avitaminosis A have been observed in infants 

 with congenital biliary atresia*- and giardiasis,*^ the above-mentioned con- 

 ditions usually do not interfere to the extent of causing outspoken mani- 

 festations of the deficiency state. 



6. Hepatic Dysfunctions 



Cirrhosis and other types of injury to the liver alter the capacity of this 

 organ to store vitamin A, to convert vitamin A esters to vitamin A alcohol, 

 or to release the latter in normal amounts to the circulating plasma. There 

 is also evidence that a great variety of fatal diseases alter the normal func- 

 tions of the liver in the metabolism of vitamin A. Of particular interest in 

 this connection are the analyses of vitamin A reserves in the liver of 745 

 human subjects carried out by Moore and Sharman,*^ leading to the con- 

 clusion that "in most fatal diseases at least half the vitamin A reserves dis- 

 appear"; only in thyroid disease and diabetes were liver reserves higher 



s9 S. W. Clausen, Harvey Lectures 38, 199 (1943). 



so S. Specter, C. F. IVIrKhaiiii, atul E. R. Mesorvo, Am. J. Diseases Children 66, 376 



(1943). 

 81 H. A. Rafsky and B. Newman, Gaslroenteroloqy 10, 1001 (1948). 

 "2 M. D. Altschule, Arch. Pathol. 20, 845 (1935). 



83 P. V. Veghelyi and F. J. Lancos, Am. J. Diseases Children 78, 257 (1949). 

 8' T. Moore and I. M. Sharman, Brit. J. Nutrition 5, 119 (1951). 



