Principles of nutrition - Vitamins
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Generalities and distribution in nature ô Vitamin A ô Vitamin C ô  Vitamin D ô Vitamin E ô  Vitamin K

 

Generalities and distribution in nature

Vitamins are essential nutrients for the human organism:  they are not obtainable via metabolic functions but must be exclusively introduced in the body through a balanced diet. They play a vital role as bio-regulators adjusting metabolic processes  and cell activity; the necessity of vitamin consumption varies according to age, the degree of physical and mental activity, physiological conditions and particular diet habits.  They are found in most foods and for this reason one can obtain the minimum requirement by eating a balanced diet, thus preventing any symptomatic conditions of diseases connected to various vitamin deficiencies.

Vitamins are characterised by their ability to be soluble and are divided into two groups: fat-soluble and water-soluble.  The fat -soluble vitamins are: A, D, E, K, and the principal water-soluble ones are Vitamins B1,  B2,  PP,  B6,  B12,  C.

 

Water-soluble Vitamins

Vitamin A

For its specific function linked to the activity of  the eye's retina and for its chemical composition, vitamin A has earned the name "retinol". It is present in animal tissue as such whereas in the vegetable group its precursors are  found in association with chlorophyl: carotenes, red and yellow pigments which are present in carrots and in certain leafy vegetables.

Carotenes are considered pro-vitamins since they are  transformed, by hydrolysis, in  vitamins in animals. The conversion of carotenes into retinol occurs in the intestinal mucous, while it is stored in the liver.

Vitamin A
As a  component of rodopsine (visual pigment ) vitamin A affects the synthesis of mucopolysaccharides.  It favours and encourages the nourishment, growth and life activities of  all body tissues, and in particular those of epithelium, mucous and eyes.
 Deficiency Excess Sources Requirements
Bone  malformations, abnormal growth rate, xeraphthalmia  (cornification of eyeball tissues)

Hemeralopia  (day blindness)

 Headaches, vomiting, skin burns, anorexia, alterations of elongated bones. Headaches, vomiting, skin burns, anorexia, alterations of elongated bones.

For an adult, the need for vitamin A expressed in micrograms is approximately 700/day.

 

Vitamin D or cholecalciferol

Just like other fat solubles, vitamin D is also absorbed in the intestines together with fats.  The main organ for storage is the liver.

There are various forms of vitamin D, however the principle ones are represented by vitamin D2 which derives from ergosterol (pro-vitamin D2 ) of  vegetable sources and by vitamin D3 which derives from7-dihedrol- cholesterol ( pro-vitamin D3) of  animal sources.  Both are transformed in an active form through photo-chemical action of the sunlight's ultraviolet rays on skin tissue.
Vitamina D
It regulates the metabolism of calcium and of phosphorous due to the process of oxidation and thereby facilitates the absorption of minerals
 Deficiency Excess Sources Requirements

Rickets (bone deformation ) in children,  osteomalcia in adults, a disease whose symptoms are caused by an intense decalcification and rarefaction of the chest bones, pelvis and limbs.

 Vomiting, diarrhoea, weight loss, kidney damage Liver, fish viscera, milk and derivatives, eggs.  It is present in the vegetable group as pro-vitamin D.  An average adult most probably absorbs a sufficient quantity of vitamin D through normal sun exposure.

With a well balanced diet and normal exposure to sunlight, it is believed that an adult needn’t consume pure vitamin D .  On the contrary, it is quite necessary to prescribe this vitamin to an infant in the first 6 months, equal to 10mg., during growth, equal to about 2,5mg and while nursing, about 10mg.

 

Vitamin E or tocopheryl

Vitamin E is found in nature in diverse forms that are chemically similar to one another.  The most active form is one defined as alpha-tocopheryl and is especially present in wheat germ oil.  These substances remain stable when exposed to light and heat ( in the absence of oxygen ) but are rapidly altered when exposed to ultra-violet rays. They are particularly sensitive to oxygen and any oxidating substance.  Tocopheryl in foods are  absorbed in the intestines by the same process as other fat-soluble elements.  If they’re administered in large quantities, the excess is eliminated through the faeces and in traces in the urine. 

Vitamin E
They function as anti- toxins preventing damage to cellular membranes
 Deficiency Excess Sources Requirements

Being difficult to observe, a vitamin E deficiency is correlated to an increase of cases relates to muscular lesions such as muscular dystrophy and to certain forms of anaemia.

 Relatively non-toxic Vegetable oils, milk and derivatives, egg yolk, meat, fish, cereals  (corn, wheat, rice), legumes and leafy vegetables.

An average allowance of vitamin  E for an adult is equal to 10mg per day.

 

Vitamin K

Vitamin K encompasses a group of substances all sharing a common hemorrhagic property.  Natural vitamin K includes  K1 and K2 while the analog synthetic substance which acts as a vitamin K, is called K3.  Vitamin K is synthesised intestinal flora bacteria; it’s contained in the  microorganisms of plants and animal.  It is utilised in the liver where it is stored in small quantities

Vitamin K
It intervenes in the process of coagulation of the blood; in fact, this vitamin is n essential component for the synthesis of various proteic elements in the liver such  as prothrombin.
 Deficiency Excess Sources Requirements

Scarce vitamin K  is principally associated to muscular and intestinal hemorrhage

 It can provoke a pathology, the so-called  thrombophlebitis, that is due to extreme coagulation  within the blood vessels. Spinach, cabbage, broccoli, peas and carrots.  Tomatoes and liver have a scarce quantity;  friut, milk and meat contain small amount as well.

For an adult about 0,6-0,8 mg. Daily of vitamin K is needed.  A new born requires a larger dose of up to 1 mg. / day.

 

Water-soluble Vitamins

Vitamin C or Absorbic acid

It is valued for its effectiveness in treating the vitamin C deficiency disease named scurvy.  Vitamin C is absorbed  in the small  intestines and is passed through the bloodstream and then stored in the liver, hypophysis, thymus and the adrenal cortex.  An excess of absorbic acid is subsequently eliminated in the urine and the faeces and through perspiration in a minimum amount.  Heat and poor storage factors tend to inactivate the efficiency of this molecule.