What is the difference between fat-soluble and water-soluble vitamins?

Vitamins are substances essentials for life that we cannot synthesize and that we inevitably have to ingest through the diet for what they are essential nutrients. The exception is vitamin D, a substance that is not always essential in the diet, since we can synthesize it in the skin from cholesterol and the action of solar radiation.

Classifying vitamins is very complicated. Are chemically very different and each one has multiple functions. There are antioxidant vitamins, such as vitamin E and vitamin C, others act as coenzymes and prosthetic groups or their precursors, such as the group of B vitamins, and some even act as hormones, such as vitamin D, which regulates mineral metabolism or vitamin A which is involved in the regulation of cell growth and differentiation. Some can even display multiple features at once.

The most used classification criterion is the solubility in water and fata very general characteristic that does not inform about its activity but does give an idea about which vitamins a certain type of food may contain and about general metabolic pathways: factors that influence their absorption, excretion pathways or storage and distribution patterns in the body. organism.

Based on this criterion, vitamins are classified into two large groups:

  1. water soluble vitamins: they are vitamins soluble in water and aqueous media, not in fat. They are vitamin C and the 8 B vitamins.
  2. fat soluble vitamins: substances soluble in lipids and fatty media, not in aqueous media. They are vitamins A, D, E and K.

water soluble vitamins

The group of water-soluble vitamins is made up of vitamin C and the eight B vitamins. all of them are soluble in water and they all act like enzyme cofactorseither as coenzymes or as prosthetic groups, in addition to being able to have other effects.

Being soluble in water, they will be dissolved in the aqueous part of the food. They are absorbed directly into the bloodstream in the enterocytes through various membrane mechanisms. The excess it is excreted through the urine and does not accumulate in the bodyexcept for vitamin B12, which is stored in liver deposits, which is why they should be consumed more frequently and regularly than fat-soluble vitamins.

The vitamin C is he ascorbic acid, specifically the L enantiomer, and is an essential substance for many types of organisms, but almost all can synthesize it, the human species cannot. In solution it is in the form of ascorbate, a powerful antioxidant acts as a substrate for the enzyme ascorbate-peroxidase. It also acts as coenzyme of several vital enzymes that catalyze collagen hydroxylation, carnitine synthesis, norepinephrine synthesis, synthesis of various hormones, and tyrosine metabolism.

The B vitamins are a chemically heterogeneous group, although all with nitrogen in their molecule, that participate in the regulation of cell metabolism:

  • Vitamin B1 (thiamin): coenzyme in the catabolism of sugars and amino acids.
  • Vitamin B2 (riboflavin): precursor of the cofactors FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide), necessary for many flavoproteins and for the activation of other vitamins.
  • Vitamin B3 (niaciona): precursor of the cofactors NAD and NADP, necessary in many metabolic reactions.
  • Vitamin B5 (pantothenic acid): precursor of coenzyme A, necessary to metabolize many molecules.
  • Vitamin B6 (pyridoxine): coenzyme in many metabolic reactions.
  • Vitamin B7 (biotin): coenzyme of carboxylases, enzymes necessary in the synthesis of fatty acids and in gluconeogenesis.
  • Vitamin B9 (folic acid): it is a cofactor of several metabolic reactions and participates in the formation, repair and methylation of DNA, especially important in the stages of greatest development, especially infancy and embryonic development.
  • Vitamin B12 (cobalamin): coenzyme necessary for the metabolism of fatty acids, amino acids and DNA synthesis.

fat soluble vitamins

Fat-soluble vitamins are present in foods that contain a relatively large fat fraction. They are absorbed in the small intestine through chylomicrons together with triglycerides, phospholipids, cholesterol and other fatty substances, so they need the bile salts and are absorbed into the lymphatic circulation before passing into the blood. They are fat-soluble vitamins vitamins A, D, E and K. All of them are stored in the liver and accumulate in adipose tissue.

Due to this accumulation, and unlike water-soluble vitamins, an adequate supply is possible without necessarily having to be consumed daily and it also makes it possible for toxic levels to be reached more easily (hypervitaminosis), especially if nutritional supplements and food are consumed. fortified.

Nutritional supplements and food additives can often be found with water-soluble forms of these vitamins that are then metabolized in the body to the active form, but they should not be confused with water-soluble vitamins.

  • Vitamin A (retinol, retinal, carotenoids): is part of rhodopsin, a pigment present in the rods of the retina that is necessary for vision, especially in low light conditions. Participates in the growth and differentiation of the eye, respiratory system and gastrointestinal system. It is necessary in osteogenesis and improves the immune response.
  • Vitamin D (calciferol): it is a precursor of calcitriol, considered a hormone since it can be synthesized completely endogenously from cholesterol and the action of the UV ration of the Sun. It increases the absorption of calcium and phosphorus in the intestine, inhibits the formation of osteoclasts (cells of bone resorption) and reduces the secretion of parathyroid hormone (PTH), its most important role is the regulation of bone remodeling, calcium homeostasis and general metabolism, but it is also involved in muscle function and immune function .
  • Vitamin E (alpha-tocopherol): acts as an antioxidant with a prominent role in the synthesis of the heme group, an essential part of hemoglobin and oxygen transport, and in the prevention of lipid peroxidation.
  • Vitamin K (phytomenadione): required in blood coagulation processes and in the formation of red blood cells.

Comparison table

fat soluble vitamins

A, D, E and K

water soluble vitamins

C and group B

Soluble in fatty medium, not in aqueous mediumSoluble in aqueous medium, not in fatty medium
They are absorbed together with lipids. Requires bile saltsabsorption is simpler
are not excretedThey are excreted in urine
They are stored in the liver and accumulate in fatty tissuesThey are not stored or accumulated (except B12)
The deficiency manifests itself when the reserves have been depletedDeficiency manifests faster with insufficient intake
Relatively high doses spaced over time can prevent deficiencyRequire more regular input
Hypervitaminosis due to excessive consumption is more likelyHypervitaminosis is unlikely; the excess is excreted
Go up