The Double-Edged Sword of Vitamin A: Function and Toxicity

Abstract

Introduction: This article investigates the essential functions and health risks of vitamin A, focusing on its metabolic pathways, dietary origins, daily requirements, the clinical consequences of deficiency and the harmful effects of overdose.

Materials and Methods: A thorough literature search was performed using PubMed and Google Scholar databases with the following keywords: "Vitamin A", "retinoids", "vitamin A deficiency", "hypervitaminosis A", "retinoic acid", "immune function", "vision", "skin health", "toxicity", and "wound healing".

Summary: Vitamin A is a fat-soluble micronutrient essential for maintaining healthy vision, a strong immune system, proper growth, reproduction, and skin integrity. It is found in two main forms: preformed vitamin A and provitamin A carotenoids. After intestinal absorption, it is primarily stored in the liver and converted into active compounds such as retinoic acid, which regulate gene expression and support epithelial health and immune function. Deficiency can result in night blindness, increased susceptibility to infections, delayed wound healing, and skin disorders. On the other hand, excessive intake, particularly from supplements, may lead to acute or chronic toxicity affecting the liver, bones, and nervous system, and can be harmful during early pregnancy due to its teratogenic effects. Ensuring adequate vitamin A intake is therefore key to supporting overall health.

Conclusions: Vitamin A is essential for human health, but both its deficiency and excess pose significant risks. Deficiency remains a major concern in low-income countries, while preventing toxicity is increasingly important in high-income populations due to widespread supplement use. Key strategies include education, nutritional screening, food fortification, and individualized supplementation. Further research is needed to define safe dosage limits and therapeutic uses, particularly for vulnerable groups like pregnant women and children.