Vitamin A Deficiency
Vitamin A is a fat-soluble vitamin which plays an important role in a number of biological processes. Vitamin A participates in the regulation of the differentiation of the epithelial tissues, embryonic development, immune system development, and the production of rhodopsin visual pigment, essential for good vision.Vitamin A can only be received by way of diet, either directly as an ester of retinol or by synthesis from provitamin A, particularly from beta-carotene.
The most common source of vitamin A is beta-carotene. Through a metabolic conversion, retinal with the participation of the monooxygenase 1 (BCMO1) enzyme and the subsequent action of the reductase enzyme, produces retinol (vitamin A). Beta-carotene is contained in human skin where it is involved in the protection against the harmful effects of UV radiation. Beta-carotene acts as an antioxidant and eliminates free radicals caused by UV radiation. Vitamin A plays an important role in skin care by helping the healthy growth of young skin cells ( keratinocytes), which make up 95% of the skin. It strengthens the skin’s health and slows the aging process by reducing the development of wrinkles.
Vitamin A (retinol) and various molecules derived from vitamin A are referred to as retinoids. Retinoids are contained in cosmetic products, having a demonstrable effect on the health of the skin and helping in the treatment of acne. Among retinoids, the most studied is the effect of tretinoin on the health of the skin. Tretinoin has proven effects in the treatment of fine wrinkles, rough skin structures, and in a decrease of hyperpigmentation.
Intake of Vitamin A by Diet
Essential esters of retinol and beta-carotene received from the diet are converted into retinol (vitamin A) in the liver. In the liver, retinol is either converted to ester and deposited or released into the bloodstream. Subsequently, retinol is transported by the retinol-binding protein into the skin capillaries in the dermis. Retinol is recaptured here by skin cells in the dermis and the epidermis through a specific receptor. Cells fibroblasts and keratinocytes convert retinol into retinaldehyde and then to retinoic acid (tretinoin). Retinoic acid effects gene expression and influences cellular processes both in the epidermis and dermis. Therefore, retinoic acid has a strong effect on the health and appearance of the skin.
Vitamin A Deficiency
Deficiency of beta-carotene results in a decrease in the general immunity of the body and a reduced vitamin A production. When vitamin A is not taken directly from the diet, severe health complications associated with blindness and death from common infections occur due to decreased immunity. Vitamin A deficiency is rare while maintaining normal eating habits and may instead be caused by a disorder associated with the synthesis of this vitamin. One of the key processes leading to vitamin A production is the conversion of beta-carotene into retinal with the participation of the BCMO1 (beta-carotene 15,15'-monooxygenase) enzyme. The decline in enzyme activity of BCMO1 is associated with a decreased capability to convert beta-carotene into retinal, resulting in insufficient vitamin A production.
Factor associated with vitamin A deficiency
Studies show a strong association between the intake of beta-carotene (a source of vitamin A) in the form of food supplements and an increased risk of lung cancer in smokers. On the contrary, carotenoid intake by way of the diet is associated with a probable decreased risk of lung, mouth, pharynx, and larynx cancer. Therefore, beta-carotene intake is recommended through diet, not in the form of food supplements. Avoid using high doses (> 18 mg) of β-carotene supplements, particularly if you smoke.
Vitamin A and Overdose
Vitamin A can cause hypervitaminosis, a disease caused by an excessive amount of vitamin A in the body. Vitamin A is deposited in the liver, so its excessive consumption can cause liver impairment. Intake is not recommended during pregnancy, in which it may cause foetal damage. Vitamin A is found in high amount in the livers of arctic animal (wolves, dogs, bears), which led to the intoxication (often fatal) of polar expeditions that had exhausted their food supplies and turned to eat hunting wild animals. Hypervitaminosis manifests itself by vomiting, diarrhoea, nausea, and bleeding of the lips.
Carotenosis may occur as a result of excessive consumption of carotenoids which results in orange skin colouration. Carotenoids (particularly beta-carotene), in case of overabundance, are deposited in the top layers of the skin. Unlike vitamin A, an overdose of carotenoids has no serious side effects.
Pregnancy and Vitamin A
Vitamin A is one of the few vitamins which may lead to hypervitaminosis, a disease caused by the abundance of vitamin A. Studies have demonstrated that excessive consumption of vitamin A is dangerous during pregnancy and has considerable teratogenic effects (potential to damage the developing foetus). In pregnancy, it is recommended to avoid an increased Vitamin A intake and the application of cosmetic products containing vitamin A (ointments with retinoids curing psoriasis, etc.). For any use during pregnancy, consult your doctor. Natural provitamin A (beta-carotene) should be free of side effects.