Calcium Metabolism in Old Age 119 



One assumption obviously not completely valid was that 

 adaptation had been fully developed and that it had reached 

 its maximal power. The three approximations used were 

 the following: 



1. The "true" percentage absorption was calculated 

 according to formulae (see Fig. 1 and Nicolaysen, Eeg-Larsen 

 and Malm, 1953). 



2. It was assumed that this calculated percentage would 

 be the same when the level of intake varied somewhat up or 

 down. 



Two examples will illustrate the procedure. 



1. No. 273: 20 mg. — — =28 mg. which added to the 



349 mg. results in the figure used. 



2. No. 121: 49 mg. ——=69 mg. which subtracted from 



450 mg. results in the figure used. 



3. In a few persons a slight linear correction up or down of 

 the urinary Ca was used in consequence of a more substantial 

 correction needed for intake. (See e.g. 92 and 408c.) Thus 

 in 408c., 25 mg. were added to the 186 mg. 



The balance was measured in fourteen men above fifty 

 years of age and adaptation was studied in nine men above 

 fifty years of age. 



Discussion 



Absorption and its adaptation 



It appears that the absorption is more efficient than 

 usually thought. The introduction of e.g. 300 and 900 mg. 

 respectively for the daily Ca content of the digestive juices 

 will not materially alter this contention. 



It also appears that the power of absorption is increased 

 in the course of time in practically all persons studied. This 

 contention rests on the assumption that the digestive juice 

 Ca is not systematically altered in a period of negative balance 



