Properties and functions of vitamin A

Vitamin A is an essential micronutrient for humans, meaning that it cannot be biosynthesized in the body and thus must be obtained from dietary sources.

The vitamin exists in three major forms: retinal (the aldehyde isoform), retinol (the alcohol isoform), and retinoic acid (RA), which is the irreversibly oxidized form of retinol.

Retinol empirical formula: C20H30O with molecular weight of 286.45

Retinol is soluble in fats and oils and practically insoluble in water and glycerol. Vitamin A esters are readily soluble in fats, oils, ether, acetone and chloroform. They are soluble in alcohol but insoluble in water.

Dietary vitamin A is absorbed in the small intestine in the form of retinol and transported in blood attached to retinol-binding protein (RBP). Inside the cells, retinol is oxidized into its main biologically active derivatives, first retinaldehyde (retinal), which plays a role in vision, and then retinoic acid (RA), which regulates the expression of multiple target genes.

Among other functions of vitamin A:
* Vitamin A appears to facilitate the mobilization of iron from storage sites to the developing red blood cell for incorporation into hemoglobin, the oxygen carrier in red blood cells.

*Together with the protein opsin, the 11-cis isomer of retinol forms the light -sensitive visual pigment rhodopsin located in the rod of the retina. Rod cells with rhodopsin can detect very small amounts of light, making them important for night vision.

*Animal studies shown that vitamin A is required for normal growth and development. Retinol and retinoic acid (RA) are essential for embryonic development. During fetal development, RA functions in limb development and formation of the heart, eyes, and ears.

*Another major function of vitamin A is its role in cell differentiation.

*Vitamin A often called the antireflective vitamin, is protection against infections. The skin and mucosal cells (cells that line the airways, digestive tract, and urinary tract) function as a barrier and form the body's first line of defense against infection. Retinol and its metabolites are required to maintain the integrity and function of these cells.
Properties and functions of vitamin A

Vitamin D properties

Vitamin D is a generic term for a family of compounds known as vitamins D1, D2 and D3. Chemically these substances are called sterols, and their metabolic products have the ability to prevent rickets in children or osteomalacia in adults.

Vitamin D (calciferol or activated ergosterol) is fat soluble and requires dietary fat that absorbs the vitamin from food sources or supplements in the digestive tract.

Vitamin D is neither a vitamin nor a nutrient because exposure to sunlight can provide the body's requirement for vitamin D. Vitamin D is produced within the skin that is exposed to sunshine when the ultraviolet (UV) index is at least 3.

Calciferol (vitamin D2)

Once vitamin D is formed in the skin or ingested in the diet, it enters the bloodstream and travels to the liver and kidney where it is hydroxylated on carbons 25 and 1 to form 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D), respectively.

25-Hydroxyvitamin D is the major circulating form of the vitamin that is measured to determine the vitamin D status of patients. This vitamin is necessary for normal tooth and bone formation.

There have been data from biochemical and molecular genetic studies that point to vitamin D having a much wider role than just maintenance of calcium and phosphate metabolism. Vitamin D and its synthetic analogues have been shown to have anticancer properties as well as to modulate the immune system.
Vitamin D properties

Properties of vitamin K

Vitamin K comprises derivatives of 1,4-naphthiquinone. Naturally occurring forms are equipped with structures possessing the unsaturated isoprenoid side chain linked to naphthoquinones at crabon-3.

Vitamin K also fat soluble. It is essential for the synthesis of prothrombin a compound involved in the clotting of blood.

Vitamin K is mostly needed to help to stop bleeding, but it has some other jobs as well.

It is a cofactor specific to the formation of –carboxyglutamyl residues from specific glutamate residues in certain proteins.

The most important is the crucial role vitamin K, plays building bones. Vitamin K is needed to help hold onto the calcium in bones and make sure it’s getting to the right place.

It actually comes in three different forms: First, there’s vitamin K1, or phylloquinone. This is the form of vitamin K found in plant foods.

Vitamin K1 is quite stable to oxidation and most food processing and food preparation procedures. It is unstable to light and alkaline conditions.

Next, there’s Vitamin K2, also called menaquinone. This the form friendly bacteria in the intestines make. 

The last form would be called vitamin K3. It is also called menadione. Menadione is the only formed isolated from Staphylococcus aureus and also chemically synthesized. It is a synthetic compound that can be converted into K2 in the gastrointestinal tract.

All  vitamin K ends up in liver, where it’s used to make some of the substance that make blood clot.
Properties of vitamin K

What is choline?

Choline had been isolated by Strecker in 1862 and its structure had been determine by Bayer.

It is a colorless, bitter-tasting, water soluble white syrup that takes up water rapidly on exposure to air and readily forms more stable crystalline salts with acids such as choline chloride or choline bitartrate.

Choline is crucial for the normal function of all cells. It is needed for the structural integrity and signaling functions of cell membranes; it directly affects cholinergic neurotransmitter; it is a major source of methyl groups in the diet; and is required for lipid transport form liver and for normal muscle function.

All, natural fats contain some choline; therefore, the vitamin is widely distributed in foods and feedstuffs.

The factor occurs naturally mostly in the form of phosphatidylcholine which because it is good emulsifying agent, is used as an ingredient or additive in many processed foods and food supplement.

Choline content of foods is usually determined by a colorimetric method or by microbiological assay.
What is choline?