Reserves of the Body
As we have seen, vitamins A, D, E and K are fat-soluble vitamins. Due to this characteristic they can be stored by the liver and adipose tissues. In the case of fat-soluble vitamins, there are therefore real reserves which the body can draw on in times of need.
As we have seen, vitamins B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 ​​(pyridoxine), B12 (cobalamin) and C (ascorbic acid), folic acid and biotin are all water-soluble vitamins. This class of vitamins is easily absorbed by the body which, however, is unable to accumulate them. Therefore in the case of water-soluble vitamins there are no real reserves and their intake with food must be almost constant.
Excess and Deficiency
To be absorbed, the fat-soluble vitamins require the presence of fats. It is no coincidence that the most significant sources of these substances are found in foods particularly rich in lipids such as oils, cheeses, sausages, etc. Consequently, it is logical to think that those who follow a low-fat diet may experience more or less marked vitamin deficiencies over time.
On the other hand, those who take large quantities of these substances, for example by resorting to an exaggerated dietary supplement, can go against real phenomena of hypervitaminosis intoxication.
An unbalanced diet characterized by a reduced consumption of plant-based foods can instead lead to a lack of water-soluble vitamins. In case of excessive intake there is no risk of toxicity as the vitamin surplus is easily eliminated with urine or sweat.
Finally, remember that with normal nutrition there is no risk of hyper or hypovitaminosis. The risk of hypervitaminosis is greater using supplements while the risk of hypovitaminosis rises in case of malnutrition, in case of increased need (for example during pregnancy and lactation) and in case of unbalanced diets or deficient in particular foods (ketogenic and similar ).
Food Sources
n nature there is no food that contains all vitamins. Some types of vitamins are found mainly in plant-based foods such as vegetables, fruit, cereals and legumes. Other types are contained mainly in foods of animal origin, such as meat, fish and cheeses.
For further information: Vitamin and Mineral Content of Foods
Natural and Biosynthetic: Differences
If from the structural point of view there is no difference between the vitamins of natural origin and the biosynthetic ones, the effects obtained from the intake of one or the other are different. In fact, while the former interact with numerous other natural substances present in the food that contains them, the latter, being isolated, have a lower beneficial effect. What our body needs is not a single vitamin but a complete set of all nutrients.
Integration
Athletes have not been clearly shown to have higher RDAs than sedentary (group B and antioxidants: A, C, E, beta carotene). It is believed, in fact, that the possibly higher requirement is covered by the increased food intake.
On the other hand, subjects are at risk of developing hypovitaminosis:
- following extreme low-calorie or low-fat diets
- vegetarians (or exclusion of specific foods, unbalanced diet)
- elderly athletes (difficult absorption of B12)
- low exposure to the sun (Vit. D).
