Are you sure of this? I know calcium and phosphorous absorption are regulated by Vit-D, but I was under the impression that oral Vit-D was absorbed with fats due to its fat solubility. It is transported to the liver with absorbed fats as well.
Unless calcium effects fat absorption?
Vitamin D is indeed fat soluable, and taking it with fats will enhance absorbtion. That's actually a good point that many often overlook.
Check this out as well:
Chapter 6F: Hormonal regulation of calcium and phosphate balance
Authors
Burton D Rose, MD
Theodore W Post, MD
Section Editor
Burton D Rose, MD
Deputy Editor
Theodore W Post, MD
Last literature review version 16.2: May 2008 | This topic last updated: September 14, 2000 (More)
INTRODUCTION — The maintenance of calcium and phosphate homeostasis involves changes in intestinal, bone, and renal function. Regulation of intestinal function is important because, in contrast to the complete absorption of dietary NaCl and KCl, the absorption of Ca2+ and phosphate is incomplete. This limitation is due both to the requirement for vitamin D and to the formation of insoluble salts in the intestinal lumen, such as calcium phosphate, calcium oxalate, and magnesium phosphate.
As an example, a normal adult may ingest 1000 mg of Ca2+ per day, of which roughly 400 to 500 mg may be absorbed. However, 300 mg of calcium from digestive secretions is lost in the stool, resulting in the net absorption of only 100 to 200 mg [1]. In the steady state, this quantity of calcium is excreted in the urine.
Most of the body Ca2+ and much of the phosphate exist as hydroxyapatite, Ca10(PO4)6(OH)2, the main mineral component of bone. Phosphate also is present in high concentration in the cells. Within the plasma, both Ca2+ and phosphate circulate in different forms. Of the plasma Ca2+, roughly 40 percent is bound to albumin, 15 percent is complexed with citrate, sulfate, or phosphate, and 45 percent exists as the physiologically important ionized (or free) Ca2+. Plasma phosphorus, in comparison, consists of phospholipids, ester phosphates, and inorganic phosphates. The latter are completely ionized, circulating primarily as HPO42- or H2PO4- in a ratio of 4:1 at a plasma pH of 7.40. (See "Chapter 10B: Buffers").
Although only a small fraction of the total body calcium and phosphate is located in the plasma, it is the plasma concentrations of ionized Ca2+ and inorganic phosphate that are under hormonal control. This function is mediated primarily by parathyroid hormone and vitamin D, which affect intestinal absorption, bone formation and resorption, and urinary excretion [1-6]. The physiologic roles of other hormones such as calcitonin and estrogens in the regulation of Ca2+ and phosphate balance are incompletely understood and will not be discussed further [7].
PARATHYROID HORMONE — Parathyroid hormone (PTH) is a polypeptide secreted from the parathyroid glands in response to a decrease in the plasma concentration of ionized Ca2+ [2]. This change is sensed by a specific Ca2+-sensing protein in the cell membrane of the parathyroid cells [3,8].The receptor permits variations in the plasma Ca2+ concentration to be sensed by the parathyroid gland, leading to the desired changes in PTH secretion. Polymorphisms of this receptor may underlie a significant portion of the variability observed in the serum calcium concentrations in normal individuals [9], while inactivating mutations lead to hypercalcemia because a higher plasma Ca2+ concentration is required to activate the receptor and suppress PTH release [10-12].
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Here's a more in depth read:
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I have so many studies saved on vitamin d, i just have to find them all.
