Calcium and Vitamin D

What are the main classifications of calcium?

Calcium and phosphorus and the most prevalent minerals in the body (found in larger amounts than selenium and zinc)
- regulation of calcium and phosphorus is regulated by vitamin D

Describe the effects of calcium in the bones

99% of calcium is in the skeleton
- bone: a calcium and phosphorus reservoir
- minerals are drawn from the bones when low dietary intakes reduce the circulating phosphorus or calcium concentrations

Describe the effects of calcium in circulation and extracellular fluid

<1% of calcium is in the blood circulation or extracellular fluid (ECF)
- positively charged calcium (Ca2+) and negatively charged phosphate ions are 2 primary signaling elements of cells
- these functions are protected from fluctuations in dietary calciu

Describe the significance of vitamin D in calcium and phosphorus regulation

The parathyroid gland senses circulating calcium concentrations, and the parathyroid hormone (PTH) is released when calcium is low, along with vitamin D

When circulating calcium is low, the parathyroid hormone signals vitamin D to:

Vitamin D is converted to its active form, and is signaled by PTH to absorb more dietary calcium phosphorus and reabsorb more calcium from bones and to excrete less from kidneys

When circulating phosphorus is low, the parathyroid hormone signals vitamin D to:

the active form of vitamin D is generated under conditions of low concentrations of phosphorus, independently of PTH, resulting in phosphorus conservation (vitamin D increases calcium and phosphorus absorption, reabsorption from bones and decreases phosph

What are the noncalcemic roles of vitamin D?

The active form of vitamin D (calcitriol) works through receptors in the cell nucleus;
- the vitamin D receptors link to vitamin D response elements (VDREs) that have been found in many cell types, are associated with hundreds of genes
- polymorphisms in

What are the health outcomes related to calcium and vitamin D status

The most complete evidence base for the skeletal effects of these nutrients (calcium and vitamin D) outcomes related to skeletal health were used to set the current EARs and RDAs
- the institute of medicine also identified consequences of vitamin D excess

What has vitamin D deficiency been classically associated with?

Rickets in children
Osteomalacia in adults
- both are conditions of impaired bone mineralization (characterized by "soft bones" and reduced mineral to collagen)

What are the adverse outcomes related to excess calcium?

Hypercalcemia, hypercalcuria, vascular and soft tissue calcification, kidney stones, prostate cancer, interactions with iron and zinc

What are the adverse outcomes related to excess vitamin D?

Hypercalcemia, hypercalcuria, all-cause mortality, cancer, CVD, falls and fractures

What is the difference between resorption and reabsorption?

Resorption: process of breaking down bone for calcium
Reabsorption: process of re-absorbing calcium into the bones

What is calcium balance? (since calcium is not catabolized, and distribution is straightforward, it allows us to study its retention on the bone; calcium balance)

Calcium absorbed in - calcium absorbed out
Subtract total calcium absorbed and subtract the endogenous/urinary calcium losses (not the fecal calcium, because fecal calcium is the loss and not absorbed)

Extracellular fluid of calcium concentrations is regulated by PTH and vitamin D aka: circulating calcium is tightly regulated and homeostatically maintained by PTH and vitamin D


Describe calcium and cell signaling

Calcium in the extracellular fluid (circulation) and the endoplasmic reticulum is higher than in the intracellular space
Cellular functions are activated by calcium influx into the cytoplasm (from the extracellular fluid or endoplasmic reticulum)
Once the

What does 0 calcium balance mean?

Calcium in = calcium out: net bone calcium content doesn't change; net result of bone turn over is equal to the calcium balance as determined by calcium intakes versus losses

PTH and 1,25OH vitamin D together, enhance the dietary absorption and renal reabsorption of calcium and they also cause calcium to be drawn from the bone


What is the function of calcitonin?

Counteracts PTH when circulating calcium becomes too high

Adequate vitamin D status is required for optimal calcium absorption


The body attempts to compensate for lower calcium intakes by up-regulating absorption: such that a higher proportion of total calcium is absorbed among those people on lower habitual intakes