VITAMINS 357 



lites. Since these compounds are important complcxing agents for 

 cations, this effect may control in turn the transport of calcium ions 

 to the bones. A great deal of work will be necessary to establish this 

 or any other theory on a sound foundation. 



Requirements 



Vitamin D allowances are still expressed in international units or in 

 chick units, each equal to 0.025 fig. of pure vitamin Do or D3. 



It is recommended that infants, children, young adults to the age 

 of 20, and pregnant or lactating women receive 400 units daily. In 

 cases of active rickets prescribed daily doses may range from 500 to 

 1,500 units. Growing chicks and laying or breeding chickens should 

 receive 180 and 450 chick units of vitamin Dg/lb. of feed. The allow- 

 ance for young and breeding turkeys is 800 chick units/lb. of feed. 

 Swine require 135 to 625 units, depending on size, and cattle about 

 300 units/ 100 lb. of body weight. 



The best natural sources of vitamin D are the oils of fish livers. 

 Egg yolks are fairly good, but milk is poor. Hence it is becoming 

 more common in western countries to enrich milk and margarine. 

 Individuals with a reasonable proportion of their skin area regularly 

 exposed to sunlight require little or no supplementary vitamin D. 

 That formed in the skin as a result of the irradiation can be quite 

 ample, as shown by examination of people living outdoor lives in 

 warm climates. 



Continued excessive doses of vitamin D are hazardous, producing 

 abnormalities of bones and teeth as well as kidney stones. This rather 

 rare result has been obtained experimentally and observed on occasion 

 in children inadvertently given too much of this material. 



Deficiency 



The deficiency disease rickets is primarily a disease of growing bone 

 with the abnormality occurring at the final stage of mineralization. 

 As a result bones may become flexible and misshapen, leading to 

 enlarged skulls and joints, knock-knees or bowlegs, beaded ribs, and 

 protruding chest. Muscular impairment, poor tooth development, and 

 pot bellies are other standard results. 



These symptoms are characteristic of rickets in young and growing 

 animals and may be observed in pregnant or lactating females. The 

 disease is still fairly prevalent among women in many parts of India, 

 China, Egypt, and other countries with low living standards and a 

 custom of keeping women indoors or completely clothed, thereby 



