Vitamin A has many important functions in the human body, among others, it is responsible for proper vision, supports the immune system and also has antioxidant properties.
Vitamin A belongs to the group of fat-soluble vitamins. It is supplied to the body with food or in the form of dietary supplements, and then it is accumulated in the liver. Both its deficiency and excess can be dangerous for the proper functioning of the entire body.
Vitamin A - what is it?
Vitamin A is a derivative of carotene, belonging to the group of carotenoids.
We can distinguish three active forms of vitamin A, which have different biological activity. These include retinoic acid, retinal (11-cis-retinal) and beta-carotene.
Retinoic acid acts as a steroid hormone - it attaches to chromatin and enhances the synthesis of proteins that control the growth of cells and epithelial tissue and their differentiation.
In turn, retinal binds to opsin, a photosensitive membrane receptor. This leads to the formation of rhodopsin, which is a dye associated with seeing in the dark. Rhodopsin is present in the rods of the retina.
Beta-carotene is the strongest vitamin A precursor. It belongs to antioxidants and fights free radicals.
In the body, it is accumulated mainly in the liver and adipose tissue. Along with ingredients such as vitamin D, E and K, it belongs to the group of fat-soluble vitamins. Thus, its excess in the body may turn out to be toxic.
Sources of vitamin A in food
Vitamin A is present in both animal products (in the form of retinol) and plant components (in the form of beta-carotene).
Animal products that are a source of vitamin A include:
- offal (mainly liver),
- dairy products (mainly rennet and ripened cheeses).
In turn, in food of plant origin, vitamin A can be found in products such as:
Vitamin A can also be found in other fruit and vegetables distinguished by their yellow to red color.
Vitamin A properties
Vitamin A is essential for the proper functioning of the whole system. It plays a number of vital roles, namely, it can:
- be responsible for the proper functioning of cell membranes, regulate the growth of epithelial tissue and promote the regenerative capacity of the body's cells,
- take care of the proper functioning of the immune system,
- be responsible for the good condition of hair and nails,
- thanks to the production of collagen fibers and melanin biosynthesis, it can maintain the proper condition of the skin,
- have a key function in the vision process - reduce the risk of night blindness and macular degeneration (AMD), and may also slow down the process of vision deterioration,
- protects the epithelium of the respiratory system from microbes,
- have antioxidant properties, fight free radicals that accelerate the aging process, and reduce oxidative stress,
- have anti-inflammatory and antiproliferative effects.
Vitamin A is also used in cosmetics. Products rich in this compound can remove excessive keratosis of the epidermis, take care of proper nutrition and skin condition. It is used in firming and anti-wrinkle cosmetics. In addition, it is used in the treatment of acne.
It is also a valuable ingredient in the diet of athletes. Vitamin A is involved in the synthesis of adrenal hormones that ensure proper muscle function. In addition, micronutrient can participate in protein synthesis.
Vitamin A deficiency
Vitamin A deficiency is not a common phenomenon, because the amount of the ingredient stored in the liver is sufficient for 3-4 years.
However, the symptoms of vitamin A deficiency may be as follows:
- visual disturbances i.a. night blindness or excessive drying of the cornea and conjunctiva of the eye
- dry skin,
- fragility of hair and poor condition of nails,
- prolonging the wound healing process,
- increased susceptibility to bacterial and viral infections,
- lack of appetite.
The effects of vitamin A deficiency can be particularly dangerous for children, as insufficient supply of micronutrient can cause growth inhibition.
Excess vitamin A
Excess vitamin A in the body is also harmful and can be teratogenic. The recommended intake of a micronutrient may be exceeded, i.a. as a result of incorrect supplementation.
Symptoms of excess vitamin include:
- hair loss,
- damage to mucous membranes,
- liver enlargement and damage,
- skin lesions incl. dryness and itching,
Vitamin A requirement
The demand for vitamin A depends on age, gender and physiological state
An increased supply of the ingredient may be necessary among people with diseases of the digestive system, with prolonged stress or chronic infection, as well as when using a low-fat diet. In addition, a greater need for a micronutrient is observed among pregnant and lactating women.
Among women, the recommended daily intake of vitamin A is 700 ug per day, while among men - 900 ug. Pregnant women should take 770 µg a day, while lactating women - 1300 µg.
Dietary supplements containing vitamin A
Although vitamin A is commonly found in various animal products and foods of plant origin, additional micronutrient supplementation is sometimes indicated. Taking preparations containing vitamin A is recommended, i.a. in case of deficiency of the ingredient.
Vitamin A can be taken in the form of capsules, tablets or drops. A good source of the ingredient is also fish oil, often obtained from cod liver.
Since it is a fat-soluble vitamin, it is recommended to take it along with high-fat products, which will increase its bioavailability.
Often, vitamin A is supplemented with vitamin E. Simultaneous intake of both ingredients may enhance the protective effect against free radicals.