294 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1942 



Most of the work on iodine requirements has been done directly 

 on human beings. One reason for this is undoubtedly due to the 

 fact that it is difficult to produce an iodine deficiency in experimental 

 animals although many farm animals in the goiter region suffer fi-om 

 iodine deficiency. Balance studies (6) show that 50 to 100 micro- 

 grams of iodine per day may be sufficient. The value generally given 

 is 2 micrograms per kilogram of body weight. There is ample evi- 

 dence that these small requirements may not be met by foods and 

 drinking water. In order to meet this difficulty the fortification 

 of salt was started in this country over 15 years ago. This was the 

 first fortification program in this country. Sufficient Nal or KI 

 is added to maintain the iodine content of salt at 0.015 percent. 



Turning then to a discussion of the vitamins we find even more 

 conflicting data. The main difficulty encountered is that there are 

 several different chemical compounds which may have similar phys- 

 iological effects. Yet the quantitative activity of these different 

 compounds varies to a considerable extent. In the case of vitamin 

 A our foods contain both the classical vitamin A and carotene, as well 

 as other related carotenoids. A value of 5,000 I. U. has been sug- 

 gested on the basis that the average diet supplies one-third of the 

 total activity in the form of vitamin A and two-thirds in the form 

 of carotene. Two thousand I. U. of vitamin A as such will un- 

 doubtedly meet the daily needs. Some day it may be advisable to set 

 specific standards for the carotene requirement and the vitamin A re- 

 quirement and to express the distribution of both these compounds 

 in our food materials. The absorption of vitamin A from the in- 

 testinal tract is definitely related to the fat content of our diet and the 

 actual requirem^ent may differ drastically depending upon the presence 

 of other materials in the diet. 



The vitamin D requirement, as I have mentioned, is dependent 

 upon the total calcium and phosphorus intake as well as the calcium 

 and phosphorus ratio and may differ considerably depending upon 

 whether the diet contains ample quantities of milk or whether the 

 diet is low in this food. Apparently the different forms of vitamin 

 D do not vary sufficiently to make this a problem in human studies. 

 I believe we are safe in accepting a value of 400 I. U. per day. 



No requirements have been stated for vitamins K or E because so 

 little information is available. Under normal conditions there is 

 sufficient synthesis of vitamin K in the intestinal tract to meet the 

 requirement. However, any change in the intestinal flora might bring 

 about a definite increase in the need for preformed vitamin K in the 

 diet. 



The vitamin C requirement is rather definitely established because 

 the chemist has been able to determine this factor rather simply not 

 only in foods but also in the blood stream. Several groups of workers 



