248 VITAMIN D GROUP 



This condition is characterized by a symmetrical distribution of thinning 

 and pitting defects in the dental enamel. Although the relationship of 

 rickets to the incidence of caries has still not been established, it is generally 

 recognized that rickets results in enamel defects in the teeth which in turn 

 predispose to caries. This disabling disorder may be best prevented by the 

 ingestion of a calorically adequate and well-balanced diet, along with ade- 

 quate amovuits of vitamin D.^^' ''^ 



VII. Chemical Pathology and Pharmacology 



BENJAMIN KRAMER and ABRAM KANOF 



The chemical pathology of vitamin D deficiency is concerned with the 

 role which lack of this vitamin plays in preventing or delaying calcification. 

 In the last analysis rickets prevention depends upon the maintenance of a 

 normal concentration of calcium and inorganic phosphorus in the plasma 

 and presumably in the tissue fluids, thus in a large measure ensuring a 

 constant and adequate supply of these elements for mineralization of newly 

 formed cartilage matrix and osteoid. Exceptions to this rule are seen in the 

 very rapidly growing premature or newborn or in chronic nephritis or 

 hyperparathyroidism. An understanding of the mechanism of rickets pre- 

 vention therefore involves an understanding of the mechanism of calcium 

 and inorganic phosphorus, homeostasis. There are four facets to this prob- 

 lem: (1) the mechanism of absorption of calcium and inorganic phospho- 

 rus from the gastrointestinal tract; (2) the factors determining the level 

 of these elements in the blood; (3) the role of the kidneys in calcium and 

 phosphorus homeostasis; and (4) the factors which determine deposition 

 of calcium salts in the cartilage and osteoid, and the resolution of these 

 same materials (the local factor). 



Just how calcium and inorganic phosphorus are absorbed from the gas- 

 trointestinal tract is unknown. We do know that soluble salts of calcium 

 are more readily absorbed than the less soluble combinations. A shift of 

 the pH of the intestinal contents to the acid side favors absorption, prob- 

 ably through conversion of the less soluble alkaline salts to the more soluble 

 acid forms. The presence of large amounts of fats, especially the higher 

 fatty acids, gives rise to highly insoluble calcium salts, while an excess of 

 carbohydrate, by increasing fermentation, shifts the pH of the intestinal 

 contents to the acid state and may give rise to the more volatile and more 

 soluble lower fatty acids. 



78 M. C. Agnew, R. C. Agnew, and F. F. Tisdall, J. Am. Dent. Assoc. 20, 193 (1933). 

 " A. F. Hess, H. Abramson, and J. M. Lewis, Am. J. Diseases Children 47, 477 (1934). 



