XII. REQUIREMENTS 129 



the rate of growth or of the level or character of metabolism. Tn this group 

 are fasting and inhibition of appetite due to a deficiency of thiamine or of 

 other nutrients. 



Undou))tedl,y there are many ways in which the metabolism of lipids is 

 affected with a concomitant change in the rate of turnover of choline- 

 containing phospholipids and in the rate of utilization of choline. Further- 

 more, the demand for methyl groups in the synthesis of creatine and of 

 other methylated metabolites may divert part of the dietary supply of 

 choline to such uses. On the other hand, choline may spare methionine as 

 a source of methyl and thus allow additional amounts of this amino acid 

 to be used in protein synthesis, directly or after conversion of its sulfur to 

 cystine. Certainly, the need of choline is increased during growth. 



The position of choline among dietary essentials is uniciue and at the 

 same time anomalous. Clear-cut evidence for activity as a biocatalyst is 

 lacking, but there can be no ciuestion regarding its nutritional importance 

 in very fundamental biochemical systems in association with vitamins and 

 other indispensable nutrients. 



B. REQUIREMENTS OF HUMAN BEINGS 

 W. STANLEY HARTROFT, COLIN C. LUCAS, and CHARLES H. BEST 



Although some data are available which make possible a rough estimate 

 of the choline rec^uirement of the rat, dog, and poultry, there are no com- 

 parable data for man. The daily choline intake of adults eating average 

 mixed diets was determined in Toronto^ by actual analysis of representative 

 servings. The \'alues found (ranging from 250 to 600 mg.) are in good agree- 

 ment with calculated values of 300 to 500 mg. reported from Sweden by 

 Borglin.- The choline intake of young men on a constant, adequate diet 

 was determined in the United States by Johnson ei al.^ for a 5-day period; 

 it varied from ()24 to 899 mg., with a mean value of 737 mg., or about 150 

 mg. per day. 



Borglin- found the excretion of choline by adults to vary normally be- 

 tween 2 and 4 mg. per day, i.e., 0.5 % to 1 % of the intake. He noted that, 

 when the intake was reduced (e.g., star^'ation, ulcer diet) the amount 

 excreted fell. Dietary factors (e.g., fat, methyl acceptors) which increase 

 the refiuirement for choline I'educed the choline excretion. Conversely, 

 diets rich in lipotropic agents (protein, methionine, betaine) increased the 

 excretion of choline, obviously indicating a lessened requirement for choline. 

 These findings in human subjects paralleled those made during his investi- 



1 J. H. Ridout, C. C. Lucas, J. M. Patterson, and C. H. Best, Biochem. J. 52, 79-83 

 (1952). 



2 N. E. Borglin, Acta Pharmacol . Toxicol. 3 Siippl. 1, 1-123 (1947). 



» B. C. Johnson, T. S. Hamilton, and H. H. Mitchell, J. Biol. Chem. 159, 5-8 (1945). 



