Fat-soluble vitamins: what they are, where they are found and what they are for

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Elia Tabuenca García

What are fat-soluble vitamins, where are they found, what they are for and what deficiency and excess entail

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Vitamins are essential and indispensable molecules for the proper functioning of our body. They are divided into fat-soluble and water-soluble: let's see which are the fat-soluble vitamins, where they are found and what they are used for.


What are vitamins

Vitamins are essential molecules: our body - with rare exceptions - is unable to produce them and therefore they must be supplied by food.

These are molecules with no energy value but which play one or more indispensable roles for the growth, structural integrity of the cells and for the carrying out of metabolic processes.

Although a few milligrams of vitamins per day are sufficient, the deficiency is more frequent than one might think.

Vitamin deficiencies derive above all from incorrect and monotonous diets, from the consumption of packaged or badly stored foods and from disorders related to intestinal absorption and digestion.

In some moments of life (growth, pregnancy and breastfeeding), in certain pathological states or if certain drugs are taken, the need for vitamin increases and, if it is not satisfied, it can become deficient.

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Vitamins are divided into 13 groups which include molecules with chemical biological structure and effects. Based on their affinity for water or fats, vitamins are then divided into fat-soluble and water-soluble.

Fat-soluble vitamins, what are they

Fat-soluble vitamins, as the name implies, are molecules related to fatty substances. These are vitamins A, D, E and K, molecules responsible for the integrity of the membranes of our cells. Vitamin K also plays a fundamental role in the synthesis of some important proteins in blood clotting.

The fat-soluble vitamins found in food are absorbed in the intestine together with lipids and transported in the blood thanks to lipoproteins called chylomicrons or linked to specific proteins.

In case of excess, the fat-soluble vitamins are stored in the tissues and give rise to phenomena of hypervitaminosis, which are quite rare.

Vitamin A

La Vitamin A or retinol it is a vitamin present in foods of animal origin but also in some plants.

I carotenoids, precursors of vitamin A, are contained in tomatoes, carrots, chili peppers, yellow pumpkins, apricots, melons, peppers and many other foods. In a balanced diet, about 75% of Vitamin A comes from carotenoids.

Vitamin A is involved in cell differentiation, in the immune response, in the mechanism of vision and also has an antioxidant action.

Il requirements Average Vitamin A for the adult population is 600-700 micrograms (μg) per day. There shortage leads to keratenization of the cornea, conjunctiva and epithelial tissues, as well as precancerous changes in cells, disturbances in night vision and increased susceptibility to infections. In high doses it causes dry skin and, in pregnancy, to malformations of the fetus.

Vitamin D

La Vitamin D or calciferol it is found in foods of animal origin but is also produced by the irradiation of 7-dehydrocholesterol present in the skin with ultraviolet rays.

This vitamin promotes the absorption of calcium and phosphorus allowing adequate levels of these two minerals for proper ossification.

Il requirements it is about 15 μg per day, but it varies according to how much this vitamin is supplied by exposure to the sun's rays.

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La shortage leads to improper bone mineralization and, in children, leads to rickets.
Excess can lead to nausea, hypercalcemia and soft tissue calcifications.

Vitamin E

La Vitamin E or tocopherol it is found in vegetable oils, particularly in grapeseed and sesame wheat germ oils, in oil seeds and dried fruit, including almonds and hazelnuts.

It has an antioxidant action on membranes, protecting them from lipid peroxidation caused by free radicals. In addition, platelet aggregation decreases. It prevents the onset of cardiovascular diseases, neurodegenerative diseases and some types of cancer.
Its benefits increase with the intake of foods rich in Vitamin A, Vitamin C and flavonoids.

Il requirements of Vitamin E is equal to 12-15 mg of alpha tocopherol per day. There shortage it is quite rare and at high doses it can interfere with the absorption of vitamins A and K.

Vitamin K

Vitamin K is found in the lipid fraction of many foods, including of vegetable origin such as kale, turnip greens, spinach and broccoli.

One form of Vitamin K (Menaquinone or K2) is produced by bacteria in the intestine, and is therefore of endogenous origin.

It is also called a coagulation factor due to its role as a coenzyme in blood clotting.

Il requirements is about 140 μg per day. Since it is a vitamin present in many foods and also produced in the intestine, the shortage in adults it is rare.

A healthy, balanced diet typically provides all the vitamins we need. In particular situations and in case of pathologies it is possible to evaluate the integration by consulting your doctor.

Sources of reference: Karger / Larn

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