Vitamin D and Growth1

Abstract

In a series of experiments with young rats, it was found that a low-Ca diet adequately supplied with phosphorus and other dietary essentials presented optimum conditions for eliciting the maximum growth differential which can be obtained with vitamin D. This effect of the vitamin was accompanied by a decrease in serum inorganic P, an increase in serum Ca, a decrease in the percentage of bone ash, an increase in the organic matrix of bone, and a slight increase in the width of the cartilaginous metaphyses. Vitamin D always tended to bring the serum P to a normal level. On the other hand, its only effect on the level of serum Ca was to increase it. It was found impossible to duplicate the growth-promoting effect of vitamin D by varying the amount and proportion of P and Ca in the diet. The effect was the same, whether Ca was given as the carbonate or as the chloride. While the sole addition of Ca to a low-Ca, adequate-P diet increased growth, such additions when given continuously, or in successive increments, could not raise growth to the level induced by vitamin D alone. Also, when the dietary Ca/P ratio was raised too high, i.e. to an approximate ratio of 4.5 to 1.0, vitamin D depressed growth. The large increase in soft tissue, as well as of organic bone, when vitamin D is given, suggests that it facilitates other reactions than those concerned with the intestinal absorption and the skeletal deposition of mineral elements. It appears that the weanling rat requires vitamin D for optimum performance.