Vitamin D (long post)

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Hello,

 

firstly, thanks for the welcome. I'm pretty sure I will enjoy being

here.

 

I was reading the posts about vitamin D, so did some research and

came across this:

 

Like most vitamins, vitamin D may be obtained in the recommended

amount with a well-balanced diet, including some enriched or

fortified foods. In addition, the body manufactures vitamin D when

exposed to sunshine, and it is recommended people get 10 to 15

minutes of sunshine 3 times a week.

(http://adam.about.com/reports/000277.htm)

 

Chemistry: There are two chemical forms of vitamin D, namely vitamin

D2 (sometimes referred to as ergocalciferol) and vitamin D3

(sometimes referred to a cholecalciferol). The natural form of

vitamin D for animals and man is vitamin D3 that is produced in their

bodies from cholesterol and 7-dehydrocholesterol. An alternative

vitamin D2 is derived from the yeast sterol ergosterol by chemical

procedures.

The molecular structure of vitamin D is closely allied to that of the

classical steroid hormones, e.g. cortisol, estradiol, progesterone,

aldosterone, and testosterone (1). All steroid hormones and vitamin

D3 are chemically related to the well known sterol cholesterol.

Cholesterol in animals and man is a precursor substance for all

steroid hormones and as well vitamin D3.

 

Since vitamin D3 is produced in the skin after exposure of 7-

dehydrocholesterol to sunlight, the human does not have a requirement

for vitamin D when sufficient sunlight is available. Man's tendency

to wear clothes, to live in cities where tall buildings block

adequate sunlight from reaching the ground, to live indoors, to use

synthetic sunscreens that block ultraviolet rays, and to live in

geographical regions of the world that do not receive adequate

sunlight, all contribute to the inability of the skin to

biosynthesize sufficient amounts of vitamin D3 (5). Thus, vitamin D3

does become an important nutritional factor in the absence of

sunlight. It is known that a substantial proportion of the U.S.

population is exposed to suboptimal levels of sunlight. This is

particularly true during winter months (6;7). Under these conditions,

vitamin D becomes a true vitamin which dictates that it must be

supplied in the diet on a regular basis.

 

Since vitamin D3 can be produced by the body and since it is retained

for long periods of time by animal tissues, it has been difficult to

determine with precision the minimum daily requirements for this fat

soluble vitamin. The requirement for vitamin D3 is also known to be

dependent on the age, sex, degree of exposure to the sun, season, and

the amount of pigmentation in the skin (8).

 

Animal products constitute the bulk source of vitamin D that occurs

naturally in unfortified foods. Salt water fish such as herring,

salmon, sardines, and fish liver oils are good sources of vitamin D3.

Small quantities of vitamin D3 are also found in eggs, veal, beef,

butter, and vegetable oils while plants, fruits, and nuts are

extremely poor sources of vitamin D. In the United States,

fortification of foods such as milk (both fresh and evaporated),

margarine and butter, cereals, and chocolate mixes help in meeting

the adequate intake (RDA) recommendations (11). Because only fluid

milk is fortified with vitamin D, other dairy products (cheese,

yogurt, etc.) only provide the vitamin that was produced by the

animal itself.

 

The commercial production of vitamin D3 is completely dependent on

the availability of either 7-dehydrocholesterol or cholesterol. 7-

Dehydrocholesterol can be obtained via organic solvent extraction of

animal skins (cow, pig or sheep) followed by an extensive

purification. Cholesterol typically is extracted from the lanolin of

sheep wool and after thorough purification and crystallization can be

converted via a laborious chemical synthesis into 7-

dehydrocholesterol. It should be appreciated that once chemically

pure, crystalline 7-dehydrocholesterol has been obtained, it is

impossible to use any chemical or biological tests or procedures to

determine the original source (sheep lanolin, pig skin, cow skin,

etc.) of the cholesterol or 7-dehydrocholesterol.

Next the crystalline 7-dehydrocholesterol is dissolved in an organic

solvent and irradiated with ultraviolet light to carry out the

transformation (similar to that which occurs in human and animal

skin) to produce vitamin D3. This vitamin D3 is then purified and

crystallized further before it is formulated for use in dairy milk

and animal feed supplementation. The exact details of the chemical

conversion of cholesterol to 7-dehydrocholesterol and the method of

large-scale ultraviolet light conversion into vitamin D3 and

subsequent purification are closely held topics for which there have

been many patents issued (2).(http://vitamind.ucr.edu/milk.html)