What are water-soluble vitamins?
Water-soluble (water-soluble) vitamins are not stored and are eliminated in the urine. They include the following:
- vitamin B. There are 8 vitamins B essential to the human body and each has its own chemical composition. However, they perform similar functions and are found in many common foods. They are divided into the following family of compounds:
- vitamin B1 (thiamine)
- vitamin B2 (riboflavin)
- vitamin B3 (niacin, vitamin PP, nicotinic acid, niacinamide)
- vitamin B5 (pantothenic acid)
- vitamin B6 (pyridoxine, pyridoxal and pyridoxamine)
- vitamin B8 (biotin, vitamin B7, vitamin H)
- vitamin B9 (folic acid, and folinic acid)
- vitamin B12 (cyanocobalamin, hydroxycobalamin)
- vitamin C (ascorbic acid)
This simple classification according to solubility reflects to some extent the bioavailability of vitamins, since solubility affects their mode of intestinal absorption and their uptake by tissues.
Solubility properties are also related to the distribution of vitamins in the various food groups and have a direct relationship with the analytical methods used for their detection.
Characteristics of water-soluble vitamins
Water-soluble vitamins have the following main characteristics:
- They are water-soluble substances, therefore they are free in the food bolus and are absorbed and transported to the liver by the portal vein.
- They are not stored in large quantities, with the exception of vitamin B12, which is stored in the liver.
- They are regularly required in the diet, and their excess is generally not toxic, as they are excreted in the urine.
- Most of them are thermolabile and most of them are lost during cooking.
Digestion and absorption of water-soluble vitamins
Most of these vitamins do not require digestion and are absorbed directly by the intestine, although in some cases they are bound to proteins (as in the case of B8, B9 and B12) and require proteolysis, or they are phosphorylated and have to be dephosphorylated for absorption.
Absorption is quite effective. In the case of B12, the binding of this vitamin with a protein (intrinsic factor) is necessary for its absorption.
They do not accumulate in the body and their excess is eliminated in the urine.
Dietary sources of water-soluble vitamins
Water-soluble vitamins are abundant in foods of animal origin, except for B9 and C, which are abundant in foods of vegetable origin. Vitamin B12 is not found in vegetables and is only found in foods of animal origin (meat, offal, egg yolk, milk).
Vitamin B12 supplementation is important in vegan diets. On the contrary, in diets with hardly any vegetables and fruits, vitamin C and B9 may be insufficient.
The origin of vitamins in the body can come from the diet, but there is also an endogenous production, insufficient to maintain adequate levels, and there is also a microbial origin.
Deficiency and hypervitaminosis
Hypervitaminosis problems do not usually occur. As for deficiency states:
- vitamin B1 (thiamine): beri-beri and encephalopathy in alcoholics. Populations at risk are found in developing countries, those who use exclusively refined foods, anorexics, alcoholics, individuals with gastrointestinal disorders, and excess carbohydrates (athletes).
- vitamin B2 (riboflavin): cutaneous-mucosal, nervous and photophobia symptoms. Its deficiency is rare, it may occur in alcoholics, the elderly.
- vitamin B3 (niacin, vitamin PP, nicotinic acid, niacinamide): pellagra. There is a risk of deficiency in populations where the basis of their diet is corn (niacin not available and deficient in tryptophan).
- vitamin B5 (pantothenic acid): its deficiency is very rare. It occurs in the case of generalized malnutrition.
- vitamin B6 (pyridoxine, pyridoxal and pyridoxamine): irritability, weakness, insomnia, immunodeficiency. There is a risk of deficiency in populations where the basis of their diet is husked cereals.
- vitamin B8 (biotin, vitamin B7, vitamin H): Deficiency states of this vitamin are very rare.
- vitamin B9 (folic acid and folinic acid): megaloblastic anemias and neural tube closure defects. At risk populations are pregnant women, elderly, premature and newborns, intestinal disorders, alcoholics.
- vitamin B12 (cyanocobalamin, hydroxycobalamin): pernicious anemia and neurological disorders. People over 50 years of age and vegans are at risk.
- vitamin C (ascorbic acid): scurvy. People at risk are those who follow diets lacking in fruits and vegetables, alcoholics and drug addicts.