Retinol belongs to the A vitamins and performs important functions in the organism. It plays a central role in many enzymatic reactions. Both a deficiency and an excess of retinol cause health problems.
What is retinol?
Retinol is often equated with vitamin A in the medical literature. However, it is one active ingredient among several that perform the same functions in the organism. It therefore belongs to a group of active ingredients known as vitamin A. These chemically related active substances are a group of substances whose central substance is retinol. Chemically, retinol is a diterpenoid with a hydroxyl group, so that it belongs to the monohydric alcohols. It is derived from isoprene, which has two double bonds in the molecule. An additional feature of retinol is its beta-jonon ring, which forms a molecule with conjugated double bonds with the linked isoprene units. The conjugated double bonds play a major role in the visual process. All compounds within the vitamin A group chemically interact with each other. In addition to retinol, these active substances include retinol esters, retinal and retinoic acid. Almost all active ingredients except retinoic acid can be converted into each other. Retinoic acid is formed by oxidation from retinal. However, the reverse reaction of retinoic acid to retinal no longer occurs. Retinol can be esterified to retinol ester as well as oxidized to retinal. The respective back reactions take place constantly in the organism. Derivatives of retinol are also formed from provitamin A, beta-carotene. When vitamin A is absorbed directly, overdosage can occur. If intake is via provitamin A (beta-carotene), overdose is not possible because the organism limits the synthesis of retinol derivatives as needed.
Function, effects, and roles
Retinol, as the active ingredient of vitamin A, is indispensable for the organism because it is involved in many metabolic processes. Due to their conjugated double bonds in the molecule, retinol derivatives are important for the visual process. Furthermore, retinol ensures healthy nerve cells in all areas of the central nervous system, brain and spinal cord. Retinol is also responsible for the incorporation of iron into red blood cells. To a large extent it participates in protein metabolism. In this process it is consumed. All processes associated with an increase in protein metabolism can therefore lead to vitamin A deficiency. Retinol and its derivatives ensure normal cell growth of skin and mucous membranes. This promotes the structure and health of various organs and tissues. Skin function is maintained through healthy cell division. Retinol can also prevent DNA damage in skin cells by strengthening the appropriate repair mechanism. Retinol also plays a significant role in bone formation. For this reason, children in particular need to be adequately supplied with vitamin A. During embryogenesis, the all-trans-retinoic acid (vitamin A acid) formed from retinol is an important growth factor for embryonic nerve cells. Retinol is also instrumental in the production of the sex hormones estrogen and testosterone. At the same time, it is also responsible for sperm and egg formation, as well as for the function and structure of the oviduct and vas deferens. In addition, retinol strengthens the immune system by building effective barriers against germs, increasing the effectiveness of white blood cells and facilitating the formation of antibodies.
Formation, occurrence, properties, and optimal levels
Retinol and its derivatives (vitamin A) can be supplied to the body both directly and indirectly through beta-carotene. Within animal and human organisms, complete synthesis of retinol is not possible. Vitamin A is particularly present in animal products such as liver, cod liver oil, egg yolk, liver sausage, milk, salmon, chicken meat or pork. Provitamin A (beta-carotene) is absorbed through plant foods such as carrots, spinach, kale, pumpkin or apricots. The organism converts beta-carotene (provitamin A) into retinol and its derivatives (vitamin A) as needed.
Diseases and disorders
Both an undersupply and an oversupply of retinol lead to health problems.A deficiency of vitamin A can cause increased susceptibility to infections, eye problems, night blindness, skin dryness, loss of hair and nails, iron deficiency, arteriosclerosis, increase in the risk of cancer, increase in the risk of kidney stones, fatigue, exhaustion or bone growth disorders. There are many causes of vitamin A deficiency. For example, certain diseases can interfere with fat absorption. These include diseases of the liver, gall bladder or pancreas. In addition, inflammation or stress increases protein metabolism with increased consumption of retinol. Environmental toxins, smoking, alcohol or sunlight impair the absorption and storage of vitamin A. The conversion of carotenoids to vitamin A is also impeded in diabetes or hyperthyroidism. Some medications worsen the absorption of retinol. Sleeping pills are able to deplete the storage reserves of vitamin A in the liver. Vitamin tablets can be given to combat vitamin A deficiency. However, it is better to eat foods with sufficient vitamin A or provitamin A. Harmful environmental factors that make it difficult to absorb retinol must be reduced. An overdose of vitamin A is also harmful. This can lead to diarrhea, vomiting, headaches, enlargement of the liver and spleen and, in extreme cases, even cirrhosis of the liver. Oversupply of retinol often occurs with excessive consumption of meat products and especially liver. Increased consumption of plant foods high in provitamin A cannot lead to vitamin A overdose, because provitamin A is always converted to vitamin A as needed.
