VITAMIN D (calciferol) | Definition And Characteristics

Vitamin d 

Vitamin D is fat soluble, it comes from sunlight or food; it is sometimes called the "sun vitamin": UV rays interact with skin oils to produce vitamin D, which is then absorbed by the body. Taken orally (diet and supplements), it is absorbed with lipids by the intestinal wall.

Vitamin D is essential for healthy bones and teeth. Taken with vitamin A and C it prevents colds. It will promote the assimilation of vitamin A.

Vitamin D (calciferol) exists in two similar chemical forms: vitamin D2 or ergocalciferol, present in plants and vitamin D3 or cholecalciferol, present in products of animal origin; D2 and D3 have the same biological activity.

• Calciferols act only after their conversion into active molecules
• They are sensitive to light, acids, oxidation, which rapidly degrade them
• They are sensitive to heat (above 38 ° C)
• They are insoluble in water
• They are soluble in organic solvents, oil, fats, alcohol, ether, and chloroform

Vitamin D is not strictly speaking a vitamin since the skin synthesis covers a large part of the body, indeed if the ergocalciferol (D2) can come from the diet, most of the vitamin D is synthesized in the skin, in the form of cholecalciferol (D3), from cholesterol and under the influence of ultraviolet light from the sun.

Skin synthesis of vitamin D3 is done in the deep layers of the epidermis: 7-dehydrocholesterol is converted into provitamin D3 after exposure to ultraviolet, then it is converted to vitamin D3 by isomerization in 36h.

This skin synthesis is the main source of vitamin D for the body and depends on several factors:

• Cutaneous temperature (optimal temperature of 36.5 to 37 ° C)
• Skin pigmentation (white skins produce more vitamin D than tanned skin)
• The thickness of the epidermis in which the synthesis takes place
• The wavelength and the amount of UV radiation received
• The "age" of skin: "young" skin produces twice as much vitamin D as "old" skin
• Smog, clothing, glass windows prevent this synthesis.

Vitamin D of endogenous origin (internal) is absorbed directly by the blood vessels, the vitamin of exogenous (external) origin is first absorbed in the small intestine in the presence of fats before joining the general circulation.

 Roles of VITAMIN D:

Vitamin D (D2 or D3) follows a single path. Like steroid hormones and the final vitamin A derivative, it works by binding to receptors, penetrating the nucleus of the target cell and triggering the expression of certain genes. In other words, the vitamin here calcitriol (hormonal form of vitamin D) enters the nucleus of the cell and binds to a protein (or receptor), the couple thus formed will activate certain genes that allow the synthesis of a calcium binding protein; CaBP carries 2 calcium molecules in the intestine of the bone and kidney. Thus vitamin D regulates the absorption and the excretion of calcium in order to optimize the level.

Vitamin D plays a key role in ossification by controlling calcium absorption, bone fixation and renal excretion

It is involved in phosphocalcic metabolism:

• In the intestine it increases the phosphocalcic absorption
• In bones it increases the amount of calcium excreted in the blood
• In the kidneys it promotes the reabsorption of phosphorus

Many tissues have calcitriol receptors that also participate in:

• At the concentration of calcium in the milk at the level of the mammary gland
• Calcium transport to the fetus at the placenta
• A differentiation of white blood cells essential for the immune response
• In the synthesis of interferon, a defense agent against viruses
• At the growth of skin cells
• Muscular functioning
• At control of insulin synthesis in pancreas.

The needs of VITAMIN D:

In normal times, ie with a minimum of sun exposure (15 to 20 min / day) most of the vitamin D (50 to 90%) is produced by the skin. It is possible to build annual reserves by taking the sun every day for 10 to 15 minutes throughout the summer. The rest of vitamin D is brought in by the diet.

vitamin d foods list

Vitamin D is measured in international units or μg. Recommended daily intakes are 10μg = 400UI including 100UI of food origin.

Sources of VITAMIN D:

     Sources                        Quantity per 100g

  Milk                                    1 to 3 μg / 250 ml

  Cheese                                         2 μg

  Egg                                               4μg

 Cod liver oil (1 tablespoon)       3400

 Raw herring                                 900

 Salmon (steamed)                       500

 Canned sardines                         300

 Canned tuna                                230

 Cereals                                          50

 Chicken eggs (per egg)               40

 Butter                                            30

 Beef liver (fried)                         19

 Veal liver (fried)                         14 

VITAMIN D deficiency:

Clinical signs

• Rachitism (appears between 6 months and 2 years)
• Softening of the occipital bone, frontal and parietal bumps (6 months)
• Thoracic deformities (6 to 12 months)
• Deformations of wrists and ankles, curvature of lower limb bones, fractures (12 to 24 months)
• More rarely: tetany, convulsions
• Osteomalacia (adults)
• Osteomalacia is a demineralization of the bones, which lose calcium and phosphorus it is accompanied by:
• Bone pain (pelvis, thorax, spine)
• Muscle pain and weakness
• Transparent bone and cracks on the radio
• Later: deformities of the spine, pelvis and thorax

Lack of calcium and other nutrients involved in bone mineralization contribute to osteoporosis, which combines demineralization and bone loss.

Vitamin D deficiency results from the combination of several factors:

• Deficiency of internal synthesis due to insufficient solar exposure. Rickets and osteomalacia are still very common in social groups in which women and children leave very little and covered. To a lesser extent, deficiencies are more and more frequent among inhabitants of countries located at a latitude greater than 42 degrees north (north of the Franco-Spanish border); these inhabitants do not produce vitamin D between November and February and fail to reach the recommended daily intake (400 IU).
• Increasing needs at certain periods of life (infants, growing children, pregnant and lactating women, elderly people).
• Inadequate external inputs, although dietary vitamin D is an ancillary source, becomes important as soon as internal synthesis is reduced, needs are increased, or metabolism is disrupted.
• Inborn pathological changes or subsequent to certain treatments, metabolism or activity of calciferol.

Groups at risk and people who can benefit from supplements

• Infants and young children
• teenagers
• Pregnant and lactating women
• The elderly
• Chronic alcoholics
• Subjects with conditions causing chronic malabsorption ...
• Subjects with inherited abnormalities of vitamin D metabolism. 

vitamin d fruits 

Excess VITAMIN D:

Vitamin D shares with vitamin A, the characteristic of being slowly eliminated by the tissues of the body. Administered in high doses, it is toxic and can cause serious reactions: anorexia, nausea, weight loss, increased frequency of urination, dehydration, hypertension. These effects only occur with very large doses absorbed for several weeks. If intoxication continues, there is calcification of the tissues (kidneys, blood vessels, heart, lung)

Administration of high doses during pregnancy may result in abortion or hypercalcemia in the infant (special facies, psychomotor retardation and cardiovascular abnormalities)

Vitamin D and its derivatives are absolutely contraindicated in cases of hypercalcemia, hypercalciuria or calcium stones. 

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