From Vitamin D to Hormone D: Fundamentals of the Vitamin D Endocrine System in Relation to Good Health
from 12:00 PM to 01:30 PM
Vitamin D is essential for life in higher animals. Classically it has been shown to be one of the most important biological regulators of calcium metabolism and homeostasis via stimulating the intestinal absorption of calcium, facilitating the deposit of calcium in bone, and regulating the excretion of calcium by the kidney.
The molecular structure of vitamin D is closely allied to that of classical steroids (cholesterol) and steroid hormones (e.g., estrogens, glucocorticoids, etc). Current evidence supports the concept that the classical biological actions of the nutritionally important fat soluble vitamin D in mediating calcium homeostasis are not mediated by the parent vitamin D, but by a vitamin D endocrine system which coordinates the metabolism of vitamin D into the steroid hormone 1,25(OH)2-vitamin D (referred to here as hormone D). Hormone D, like other steroid hormones, can only generate biological responses via interacting with its partner receptor, the vitamin D receptor (VDR), to form a hormone-receptor complex. The VDR+Hormone D complex then interacts selectively with genes to regulate the production of new proteins that are involved in the appearance of beneficial biological response (e.g. stimulation of intestinal calcium absorption).
It is now clear that our body’s target organs which possess the VDR include many more tissues than just the classical intestine, bone, and kidney. The VDR is also present in the pancreas, pituitary, skin, breast tissue, placenta, hematopoietic cells, immune cells and cancer cells of various origins. Thus the collective biological actions of hormone D are much more important for good health than just good bone.
Scientists and nutrition experts agree that about half of the elderly in North America and two-thirds of the rest of the world are not getting enough vitamin D to maintain a healthy bone density that will lower their risks for fractures. Probably the nutritional Recommended Dietary Allowance (RDA) for vitamin D should be adjusted upwards from the presently approved RDA of 400 IU to levels as high as 2000 – 5000 IU/day.
Dr. Norman has been a faculty member at UC Riverside since 1963. He is currently a Distinguished Professor of Biochemistry and Biomedical Sciences, Emeriti at the UC Riverside. He has been Chair of the Biochemistry Department and Dean of the Division of Biomedical Sciences. More recently he was Chair of the UCR Academic Senate. His bibliography exceeds 800 publications.
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