Vitamin A – like vitamin D, vitamin E and vitamin K – is a fat-soluble vitamin. In colloquial language, retinol is often equated with vitamin A, but strictly speaking, vitamin A is not a single vitamin, but a group of substances. In addition to retinol (vitamin A1), this group includes retinal, retinoic acid and retinyl palmitate. Vitamin A can either be absorbed directly by eating animal foods or produced by the body from provitamin A (beta-carotene), which is found in plant foods.
Effect of vitamin A
Vitamin A is needed in our body for the maintenance of a wide variety of processes. It is particularly significant for the visual process. Here, vitamin A has an impact on night vision in particular – a deficiency can lead to night blindness. This is due to the fact that vitamin A is the precursor for various visual pigments and is therefore of great importance for color discrimination as well as light and dark discrimination. In addition, vitamin A also influences the skin and mucous membranes by promoting cell growth. In addition, it prevents DNA damage in skin cells and supports the repair of existing damage. Furthermore, vitamin A is also decisively involved in the formation of new erythrocytes. Since vitamin A promotes the growth of the skin and mucous membranes, it also has a positive effect on our immune system – because if the skin and mucous membranes are healthy, it is more difficult for bacteria or viruses to penetrate our body. In addition, vitamin A also increases the number of leukocytes and thus strengthens our immune system. That’s why even a slight vitamin A deficiency increases the risk of getting sick by two to three times.
Vitamin A is important for our bones
Vitamin A is also involved in various metabolic processes in our body. It mainly influences protein metabolism, but also fat metabolism. Because of its involvement in protein metabolism, a high-protein diet can result in vitamin A deficiency. An adequate supply of vitamin A is of great importance, especially for children. This is because vitamin A influences the formation and growth of our bones and plays a decisive role in the healing process of bone fractures in particular. But vitamin A is also important for adults, as it plays an important role in the synthesis of estrogen and testosterone. In addition, it influences oogenesis as well as spermatogenesis, and the number as well as the shape of sperm also depend on the supply of vitamin A.
Vitamin A acid
Vitamin A acid – also called tretinoin or all-trans-retinoic acid – is a degradation product of vitamin A. The acid is used, for example, in creams or alcoholic solutions used to treat acne or other skin conditions. Vitamin A acid eliminates cornification disorders, inhibits sebum production and leads to skin renewal. However, acne treatment with vitamin A acid usually has significant side effects, redness, burning, itching as well as acne flare-up may occur. Therefore, vitamin A acid therapy plays only a minor role compared to other treatment options nowadays. Furthermore, vitamin A acid is also used in various cosmetics to prevent premature aging of the skin. Premature aging of the skin is mainly caused by UV light, as it inhibits the formation of collagens and promotes the breakdown of collagen fibers. Vitamin A acid can protect the skin from both of these damaging processes and is therefore used in some anti-aging creams. However, since skin irritation can occur when using the acid, only the more harmless retinol is used in creams in Germany.
Vitamin A in food
In animal foods, vitamin A is present in one of its forms – mostly as retinyl palmitate – while in plant foods it is found in the form of provitamin A (ß-carotene). Particularly large amounts of vitamin A are found in the following foods:
- Milk
- Egg yolk
- Butter
- Liver products (especially beef)
- Fish
Provitamin A, on the other hand, is found mainly in carrot juice and raw and cooked carrots.Other plant foods that are high in provitamin A include apricots, cantaloupe melons, kale, spinach and pumpkin. Compared to vitamin A, provitamin A offers the advantage that it is converted to vitamin A in the body only when needed.
Daily requirement of vitamin A
The daily requirement of vitamin A can be met by both vitamin A and provitamin A (beta-carotene) intake. It depends on age, life circumstances and gender – in men the daily requirement is slightly higher than in women. The daily dose of vitamin A for an adult is around 1 milligram. If only provitamin A is supplied, the daily dose should be 2 milligrams. If the body is supplied with both vitamin A and provitamin A, a daily dose of 0.5 milligrams of vitamin A and 1 milligram of provitamin A is recommended. Since the vitamin does not tolerate oxygen and light well, foods containing vitamin A should always be stored in a dark place, preferably in the refrigerator. When cooking, the loss of vitamin A is between 10 and 30 percent, depending on the cooking time.
Vitamin A in pregnancy
During pregnancy, the need for vitamin A in women is slightly higher than usual. It is especially important during this time that both mother and child receive an adequate supply of vitamin A, as it has an important influence on the development of the child. However, care should also be taken during pregnancy not to take too high a dose of vitamin A, as an overdose can lead to malformations in the child. Growth disorders, liver damage, damage to the eyes as well as skin changes can occur. Since liver in particular contains large amounts of vitamin A, its consumption during pregnancy is not recommended. Likewise, one should not resort to dietary supplements containing vitamin A, such as vitamin A tablets. Taking provitamin A, on the other hand, is considered safe during pregnancy.
Hypovitaminosis: vitamin A deficiency.
If there is not enough vitamin A in the body, hypovitaminosis can occur. The risk group for vitamin A deficiency includes the elderly, young women, children who are susceptible to infection, and premature infants. Typical symptoms of hypovitaminosis are:
- Increased susceptibility to infections
- Reduced visual acuity
- Dryness of hair, nails, eyes and hair and hair loss.
- Impaired sense of smell and touch and decreased appetite.
Vitamin A deficiency can increase the risk of atherosclerosis as well as possible sequelae, cancers in organs that have a mucous membrane, fertility problems and the formation of kidney stones.
Causes of vitamin A deficiency
Just as numerous as the possible consequences are the causes of vitamin A deficiency. These include stress, inflammation and surgery, serious diseases such as cancer, arthritis or AIDS, environmental toxins, smoking, alcohol, and strong sunlight. In addition, laxatives and cholesterol-lowering drugs worsen the absorption of vitamin A, while the use of certain sleeping pills depletes vitamin A stores in the liver. In addition, individuals who suffer from diabetes or hyperthyroidism have difficulty converting plant cartinoids into vitamin A. If vitamin A deficiency is present, foods rich in the vitamin should be consumed more frequently. In addition, if a disease is the cause of the vitamin A deficiency, the disease should be treated.
Hypervitaminosis: overdose of vitamin A.
Just as with other fat-soluble vitamins, an overdose of vitamin A is harmful to health. However, an overdose can only be caused by ingesting too much vitamin A, that is, by eating too many animal foods, but not by eating too much provitamin A. This is because when we consume too many carotenoids, our body shuts down the conversion to vitamin A. However, ingesting large amounts of carotenoids can cause yellowing of the skin. In the case of an overdose, a distinction is made between acute hypervitaminosis, which is caused by taking in too much vitamin A within a short period of time, and chronic hypervitaminosis, which is caused by taking in too much vitamin A over a longer period of time. Acute overdose of vitamin A can result from, for example, large amounts of fish or seal liver. Symptoms such as headache, dizziness and vomiting may occur.If vitamin A is taken in large amounts over several weeks, this can also lead to a complete loss of body hair. If higher doses of vitamin A are taken over a longer period of time, this can have even more serious consequences: Increased intracranial pressure, excess calcium with consequences such as high blood pressure and kidney failure, proliferation of the periosteum, and enlargement of the liver and spleen can occur. Doses of vitamin A that are too high over many years cause symptoms of poisoning, which can also lead to death.
