Cholecalciferol: Wikis

  

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Cholecalciferol
Identifiers
CAS number 67-97-0
ChemSpider 9058792
EC number 200-673-2
SMILES
InChI
InChI key QYSXJUFSXHHAJI-QWSSABAFBD
Properties
Molecular formula C27H44O
Molar mass 384.64 g/mol
Appearance White, needle-like crystals
Melting point

83–86 °C

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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cholecalciferol is a form of Vitamin D, also called vitamin D3 or calciol.[1]

It is structurally similar to steroids such as testosterone, cholesterol, and cortisol (though vitamin D3 itself is a secosteroid).

One gram of pure vitamin D3 is 40 000 000 (40x106) IU, or, in other words, one IU is 0.025 μg. The upper limit (UL) for vitamin D has been recommended as 2,000 IU daily due to toxicities that can occur when taken in higher doses.[2] Daily doses greater than 2,000 IU should only be taken at the recommendation of your doctor. A 25(OH)D blood test can be taken to identify if your current intake is sufficient.

Contents

Forms

Vitamin D3 has several forms:

  • Cholecalciferol, (sometimes called calciol) which is an inactive, unhydroxylated form of vitamin D3)
  • Calcifediol (also called 25-hydroxyvitamin D3), which is the form measured in the blood to assess vitamin D status
  • Calcitriol (also called 1,25-dihydroxyvitamin D3), which is the active form of D3.

Metabolism

7-Dehydrocholesterol is the precursor of vitamin D3 and forms cholecalciferol only after being exposed to solar UV radiation.

Cholecalciferol is then hydroxylated in the liver to become calcifediol (25-hydroxyvitamin D3).

Next, calcifediol is again hydroxylated, this time in the kidney, and becomes calcitriol (1,25-dihydroxyvitamin D3). Calcitriol is the most active hormone form of vitamin D3.

Regulation of metabolism

  • Cholecalciferol is synthesized in the skin from 7-dehydrocholesterol under the action of ultraviolet B light. It reaches an equilibrium after several minutes depending on several factors including conditions of sunlight (latitude, season, cloud cover, altitude), age of skin, and color of skin.
  • Hydroxylation in the endoplasmic reticulum of liver hepatocytes of cholecalciferol to calcifediol (25-hydroxycholecalciferol) by 25-hydroxylase is loosely regulated, if at all, and blood levels of this molecule largely reflect the amount of vitamin D3 produced in the skin or the vitamin D2 or D3 ingested.
  • Hydroxylation in the kidneys of calcifediol to calcitriol by 1-alpha-hydroxylase is tightly regulated (stimulated by either parathyroid hormone or hypophosphatemia) and serves as the major control point in production of the most active circulating hormone calcitriol (1,25-dihydroxyvitamin D3).

As food fortification

Although cholecalciferol can be synthesized in the skin (see Metabolism), it is also a form of vitamin D added to fortify foods. Cholecalciferol is produced industrially by the irradiation of 7-dehydrocholesterol extracted from lanolin found in sheep's wool. In foods where animal products are not desired, an alternative compound is ergocalciferol (also known as vitamin D2) derived from the fungal sterol ergosterol.

Dose

There are conflicting reports concerning the absorption of cholecalciferol (D3) versus ergocalciferol (D2), with some studies suggesting less efficacy of D2[3], and others showing no difference[3] [4]. At present, D2 and D3 doses are frequently considered interchangeable, but more research is needed to clarify this. The "normal" 25(OH)D range is 30.0 to 74.0 ng/mL. Supplemental dosing of Vitamin D2 or D3 should maintain levels within the reference range as levels outside the range are associated with increased health risks. [5]

Stability

Cholecalciferol is very sensitive to UV radiation and will rapidly, but reversibly, break down to form supra-sterols, which can further irreversibly convert to ergosterol.

Therapeutic application

A 2008 study published in Cancer Research has shown the addition of vitamin D3 (along with calcium) to the diet of some mice fed a regimen similar in nutritional content to a new Western diet prevented colon cancer development.[6]

Alternative views

There is a minority view, often associated with Trevor Marshall, which asserts that low levels of calcifediol (25-hydroxyvitamin D3) are often due to overconversion into calcitriol (1,25-dihydroxyvitamin D3, the active form of D3) because of chronic infection rather than calcifediol deficiency.[7]

See also

References

External links








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