Vitamin A

Vitamin A encompasses a group of fat-soluble vitamins that are powerful antioxidants. This class can be divided in two main types: preformed Vitamin A and provitamin A.

Preformed Vitamin A is active as it is and it does not have to be converted; this group of ingredients is called retinoids, the main ones being retinol and retinyl palmitate.

Provitamin A class is comprised of Vitamin A precursors called carotenoids, which are converted into active retinoids by human body.

Vitamin A stregthens immune system, helps vision in dim light and keeps skin and tissues healthy. It also plays an important role in bone growth, maintains healthy neurological function and lowers lung cancer risk.

Good sources of Vitamin A are oily fish, eggs, cheese, milk, yoghurt, liver products as well as any good sources of beta-carotene including yellow, red and green vegetables and fruits.

The Most Relevant Recent Scientific Reviews

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Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age.

AUTHORS’ CONCLUSIONS: Vitamin A supplementation is associated with a clinically meaningful reduction in morbidity and mortality in children. Therefore, we suggest maintaining the policy of universal supplementation for children under five years of age in populations at risk of VAD. Further placebo-controlled trials of VAS in children between six months and five years of age would not change the conclusions of this review, although studies that compare different doses and delivery mechanisms are needed. In populations with documented vitamin A deficiency, it would be unethical to conduct placebo-controlled trials.

Positive evidence for vitamin A role in prevention of type 1 diabetes.

Type 1 diabetes mellitus (T1DM) as one of the most well-known autoimmune disease, results from the destruction of β-cells in pancreas by autoimmune process. T1DM is fatal without insulin treatment. The expansion of alternative treatment to insulin is a dream to be fulfilled. Currently autoimmunity is considered as main factor in development of T1DM. So manipulation of the immune system can be considered as alternative treatment to insulin. For the past decades, vitamin A has been implicated as an essential dietary micronutrient in regulator of immune function. Despite major advantage in the knowledge of vitamin A biology, patients who present T1DM are at risk for deficiency in vitamin A and carotenoids. Applying such evidences, vitamin A treatment may be the key approach in preventing T1DM.

Vitamin A supplementation for postpartum women.

AUTHORS’ CONCLUSIONS: There was no evidence of benefit from different doses of vitamin A supplementation for postpartum women on maternal and infant mortality and morbidity, compared with other doses or placebo. Although maternal breast milk retinol concentrations improved with supplementation, this did not translate to health benefits for either women or infants. Few studies reported on maternal and infant mortality and morbidity. Future studies should include these important outcomes.

Vitamin A and the eye: an old tale for modern times.

Clinical presentations associated with vitamin A deficiency persist in poor regions globally with the same clinical features as those described centuries ago. However, new forms of vitamin A deficiency affecting the eyes, which have become widespread, as a result of modern societal habits are of increasing concern. Ophthalmic conditions related to vitamin A deficiency require the combined attention of ophthalmologists, pediatricians, internists, dermatologists, and nutritionists due to their potential severity and the diversity of causes. As the eyes and their adnexa are particularly sensitive to vitamin A deficiency and excess, ocular disturbances are often early indicators of vitamin A imbalance. The present review describes the clinical manifestations of hypovitaminosis A with an emphasis on so-called modern dietary disorders and multidisciplinary treatment approaches. The present review also discusses the relationship between retinoic acid therapy and dry eye disease.

The neurotoxic effects of vitamin A and retinoids.

Vitamin A (retinol) and its congeners – the retinoids – participate in a panoply of biological events, as for instance cell differentiation, proliferation, survival, and death, necessary to maintain tissue homeostasis. Furthermore, such molecules may be applied as therapeutic agents in the case of some diseases, including dermatological disturbances, immunodeficiency, and cancer (mainly leukemia). In spite of this, there is a growing body of evidences showing that vitamin A doses exceeding the nutritional requirements may lead to negative consequences, including bioenergetics state dysfunction, redox impairment, altered cellular signaling, and cell death or proliferation, depending on the cell type. Neurotoxicity has long been demonstrated as a possible side effect of inadvertent consumption, or even under medical recommendation of vitamin A and retinoids at moderate to high doses. However, the exact mechanism by which such molecules exert a neurotoxic role is not clear yet. In this review, recent data are discussed regarding the molecular findings associated with the vitamin A-related neurotoxicity.