**2. Evolution of studies**

By exposure to a large number of patients with calcium and vitamin D disorders, almost inadvertently I began to pursue a slightly different direction from my mentors. I was initially working in blood pressure management and prostanoid metabolism [2] when I observed a variety of hemodynamic disturbances in these "calcium" patients [3–9]. I questioned mechanisms and consequences of my observations. I began recording case reports and performing animal physiology studies and finally dietary studies in animals and then humans. The result was an idea that calcium and vitamin D influenced the heart, the blood vessels, and the physiology of circulation. This was the beginning of considerations of extraskeletal effects of calcium and vitamin D perturbations. Of course, in my mind I feel that I was in part responsible for discovering the impact of calcium and vitamin D on multi-organ, total body physiology, and homeostasis which confers survival benefit when deficiency is corrected and supplementation is provided. From my time in the 1970s, there has been a logarithmic accumulation of observations and research trials worldwide which has expanded the horizon of calcium and vitamin D metabolism from strictly bone health to multiple organ and total body health. I will review my original studies as well as the consequences of such hemodynamic and systemic effects of calcium and vitamin D in the last chapter of this book dealing with their role in the management of ICU patients.

### **3. Conclusion**

Why is there a gap between the fads and facts with regard to vitamin D and health? For one thing, detailed pharmacokinetic measurements of vitamin D and its numerous metabolites in various populations are a relatively recent phenomenon. Secondly, it is likely that vitamin D plays a contributory role but not the primary role in disease and health beyond the known requirement to prevent rickets or osteomalacia, the main vitamin D-deficient bone diseases of children and adults, respectively. Finally, I believe more randomized controlled trials are needed to evaluate fad from fact.

### **Author details**

Edward T. Zawada University of South Dakota, United States

\*Address all correspondence to: ezawada@sio.midco.net

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**5**

*Introductory Chapter: Overview of Vitamin D Facts and Fads*

of cancer and cardiovascular disease. New England Journal of Medicine.

2019;**380**:33-44

*DOI: http://dx.doi.org/10.5772/intechopen.86669*

[1] Lee DBN, Zawada ET, Kleeman CR. The pathophysiology and clinical aspects of hypercalcemic disorders. Western Journal of Medicine.

[2] Kirschenbaum MA, Zawada ET. The role of prostaglandins in glucagoninduced natriuresis. Clinical Science.

[3] Zawada ET, Brickman AS, Maxwell MH, Tuck M. Hypertension associated with hyperparathyroidism is not responsive to angiotensin blockade. Journal of Clinical Endocrinology and

[4] Zawada ET, Bennett EB, Stinson JB, Ramirez G. The role of serum calcium in blood pressure regulation during dialysis. Archives of Internal Medicine.

[5] Zawada ET, Bennett EP, Johnson M, Bennett D. The effects of changes in calcium on blood pressure in conscious

[6] Zawada ET Jr, Johnson M. Calcium chelation and calcium-channel blockade in anesthetized acute renovascular hypertensive dogs. Mineral and Electrolyte Metabolism.

[7] Zawada ET Jr, TerWee J, McClung DE. Systemic and renal vascular responses to dietary calcium and vitamin D. Hypertension.

[9] Manson JE, Cook NR, Lee IM, et al. Vitamin D supplements and prevention

[8] Gilliland M, Zawada ET Jr, McClung DE, TerWee J. Natriuretic effect of calcium supplementation in hypertensive women over forty. Journal of the American College of Nutrition.

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*Introductory Chapter: Overview of Vitamin D Facts and Fads DOI: http://dx.doi.org/10.5772/intechopen.86669*
