Introductory Chapter: Overview of Vitamin D Facts and Fads

*Edward T. Zawada*

### **1. Introduction**

The importance of vitamin D has risen from a narrow focus on bone health to a major concern for individual and population survival due to possible extraskeletal pharmacologic effects. The latter is derived from alterations in vascular tone and multi-organ physiologic changes resulting from deficiency and restored by repletion. However, the literature is controversial because there are studies pro and con for these latter effects. Thus, there has arisen a need to try to dissect fact from fad.

I began my clinical and research interest in vitamin D measurement, physiology, and therapeutic replacement nearly 50 years ago while in training in nephrology at the University of California, Los Angeles (UCLA). It was as though the influence of Hollywood, the beach, and the star-laden music industry created a stereotype of young, beautiful, tanned, physically fit population that naturally lead to a concern with a vitamin which is activated by being outdoors, from the sunlight, from the exposure at beach. As it were, nephrology at UCLA at that time was still a newborn specialty descended from the original specialty called "metabolism." Gathered together at UCLA were many clinicians who were interested in vitamin D. Names such as Jack Coburn, Charles Kleeman, David B. N. Lee, Morton Maxwell, Nostratola Vaziri, Arnold Brickman, Francesco Llach, and Joel Koppel were those who lured me into the arena of calcium balance in health and disease. My first publication was a collaboration on a very detailed review of "The pathophysiology and clinical aspects of hypercalcemic disorders" [1]. Also developing at that same time was knowledge of the variety of hormonal and other factors that determined proper intake and serum levels of calcium, phosphorus, and vitamin D. Finally, much was being explored about the pharmacokinetics, pharmacodynamics, and excretion of these factors and the impact on bone and skeletal health.

Dialysis and transplantation would eventually emerge to consume the interest of subsequent nephrology trainees, but this was the time of the transition from the endocrinology of fluids and electrolytes controlled by the kidney and disturbed by kidney diseases to the explosion of kidney replacement strategies. The above predecessors attracted their like-minded academicians from around the world to come and lecture which included Shaul Massry, Eduardo Slatopolsky, Hector DeLuca, Ralph DeFronzo, and others. They often presented annually at the "vitamin D meeting" on the Monterey Peninsula. I was able to observe the dialog among these pioneers which filled my mind with knowledge but also questions for future investigation. What was most interesting about science that time was the indirect nature of proving that vitamin D and parathyroid hormone played such a variety of roles in kidney and other organ function and disease since both were not easily, if at all, measurable in those days. Bioassays and extractions from the liver and kidney and parathyroid glands were used in pharmacologic and dietary studies of

electrolyte balance and organ physiologic measurements to search for perturbation of physiology, response to animal models of human disease, and observations intended to detect restoration of failed homeostasis.
