VIII. REQUIREMENTS 257 



B. OF HUMAN BEINGS 



BENJAMIN KKAiMER and ABRAM KANOF 



In general terms the amount of \-itamiu D required In' any human bemg 

 is the amovmt needed to permit normal growth and mineralization of the 

 bones and teeth during infancy and childhood and to maintain these struc- 

 tures during later life, as well as to meet the increased demands of infection, 

 pregnancy, and lactation. Specifically, the determining factors for vitamin 

 D recjuirement are the ^'arying capacity of people of A'arious ages to absorb 

 and retain calcium, the rate of growth of the individual, and the adequacy 

 of the diet as regards not only the absolute amounts of calcium and inor- 

 ganic phosphorus but also the ratio of the elements to each other in the 

 diet. The nature of the compoimd of calcium or phosphorus may determine 

 the availability of the element for absorption by the intestine or utilization 

 b}' the tissues. Thus the less soluble calcium salts are more poorly absorbed 

 than are the m.ore soluble ones. In phytin the phosphorus is almost com- 

 pletely una^'ailable. Inorganic phosphorus is better absorbed than organic 

 phosphorus from the gastrointestinal tract even in osteomalacia. 



However, a high Ca/P ratio means poor phosphorus absorption, whereas 

 a very low ratio means poor calcium absorption, especially where the in- 

 testinal contents are alkaline in reaction. Similarly, any cation such as alumi- 

 num or Fe which tends to form poorly soluble phosphorus compounds will 

 interfere with phosphorus absorption. The proportions of protein, fat, and 

 carl)ohydrate in the diet influence calcium and phosphorus absorption 

 through their effect on the reaction of the intestinal contents. Little is 

 known regarding the mechanism of absorption of calcium salts, but the less 

 fa\'orable the condition for calcium and phosphorus absorption the more 

 ^'itamin D will be recjuired to ensure optimal utilization of available ma- 

 terials. 



Roughl}', the daily need for calcium is 0.1 g. throughout infancy,** 0.3 g. 

 during childhood, and 0.5 g. during adolescence.^ The actual amount re- 

 ([uired by an individual will depend directly on his rate of growth, hence 

 the tendency of the rapidly growing infant to develop rickets under condi- 

 tions in which the adult will be free of disease. The prematurely born infant 

 is born with a minimal store of calcium and phosphorus, and in addition 

 under proper conditions his rate of growth is greater than that of the full- 

 term infant. He then suffers from a double handicap, namely, a greater 

 need of bone-forming minerals and ^'itamin D, with a decreased capacity 

 for absorption of these substance. The fetal need for calcium during the last 



8 White House Conference Rejxji'ts: II Nutrition, p. 196. Century Co., New York, 

 1932. 



9 I. Leitch, Nutrition Abstr. & Revs. 6, 533 (1937). 



