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4.6.1. Fat-soluble vitamins

Fat-soluble vitamins

The fat-soluble vitamins are lipid molecules and therefore have low density, are insoluble in water and soluble in organic solvents, fats and oils. Vitamins A, D, E and K. belong to this group.

They can be stored in the liver and in the body's fat, so it is not necessary to take them every day, since it is possible, after sufficient consumption, to subsist for a time without their contribution.

If consumed in excess (more than 10 times the recommended amounts) they can be toxic.


Vitamin A or retinol

Known as an antixerophthalmic vitamin, it is found in two forms; vitamin A1, or retinol, obtained from marine fish, and vitamin A2, obtained from freshwater fish.

  • Sources. It is found in foods of animal and vegetable origin, although in these it is found in the form of a provitamin. It is found in the liver, egg yolk, dairy, carrots, spinach, broccoli, lettuce, apricots, melon. It deteriorates with cooking.
  • Action. Protects epithelial tissues: mucous membranes, skin... It is also necessary for light perception, and the formation of collagen in bones.
  • Deficit. The lack of this vitamin causes the appearance of infections in the epithelial tissues and xerophthalmia (dryness of the cornea). The lack of vitamin A produces a depletion of the amount of retinen , with the consequent loss of visual acuity, and night blindness. It also causes desiccation of the mucous membranes, as well as delayed growth and development.
  • Excess. The ingestion of large amounts of this vitamin is toxic and produces a series of alterations, such as drowning, hair loss, weakness ...

Vitamina A

By Dwmyers (en:Image:Retinol.png) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Vitamin D or calciferol

The vitamin D refers to a number of sterols: vitamin D2 , D3, D4, D5 and D6. The best known are vitamin D2 or calciferol and vitamin D3 or cholecalciferol, which are obtained from two provitamins: ergosterol and 7-dehydrocholesterol, respectively. This obtaining takes place through the action of the sun's ultraviolet rays on the skin.

  • Sources. There are three ways of obtaining it in humans:

    • By ingestion of ergosterol, a provitamin of plant origin that is transformed into vitamin D2 in the skin .

    • From 7-dehydrocholesterol (derived from cholesterol), which is secreted by epidermal glands and which is transformed on the skin into vitamin D3, which is reabsorbed.

    • By direct ingestion when taking foods that contain it, such as herring, salmon, sardines, liver extracts, milk and eggs.

  • Action. It favors the absorption of Ca2+ through the intestinal wall, the concentration of Ca2+ in the blood and its fixation in bones and teeth.

  • Deficit. Its lack causes rickets in children and osteomalacia in adults. These diseases produce a defective calcification of the bones, which soften and deform.

  • Excess. Excessive consumption of this vitamin causes digestive disorders, with vomiting and diarrhea, and calcifications of organs such as the kidney , liver, heart, etc.


Pubblico dominio, Collegamento

Vitamin E or tocopherol

  • Sources. It is found in foods of plant origin, especially in green leafy foods, in seeds , vegetable oils, butter and also in egg yolks.
  • Action. Protects membrane lipids from metabolic oxidation. It acts as a cofactor in the electronic transport chain.
  • Deficit. Hypoavitaminosis has been shown to produce, in addition to digestive and reproductive disorders, paralysis and muscular dystrophy.
  • Excess. Its excessive consumption does not produce toxicity.

Vitamina E

By Jü (Own work) [Public domain], via Wikimedia Commons

Vitamin K

            It is also called phylloquinone.

  • Sources. It is abundant in cauliflower. As it is also synthesized by intestinal bacteria, its ingestion in the diet is not essential.
  • Action. It acts in the formation of prothrombin, a process that takes place in the liver. This molecule is the precursor of thrombin, an enzyme that transforms fibrinogen into fibrin, a substance necessary for blood clotting.
  • Deficit. Vitamin K deficiencies are rare and are due to alterations in intestinal absorption, generally caused by a deficiency of bile acids responsible for the absorption of lipids in the intestine. Hypoavitaminosis favors blood clotting disorders.
  • Excess. It does not produce any disorder.

By User:Mysid (Self-made in BKChem + perl + vim.) [Public domain], via Wikimedia Commons