VITAMIN A AND THE NERVOUS SYSTEM

Vitamin A is essential for the early development and normal functioning of the brain throughout life. A deficiency of vitamin A is one of the leading causes of morbidity and mortality in developing countries, and subclinical deficiency is probably present worldwide. The main active molecule in vitamin A is retinoic acid, which is involved in vision, the immune system, skin health, olfaction and cognition (learning, memory, spatial functions, olfaction, etc.) through processes of neuroplasticity and neurogenesis. Vitamin A is involved in the regulation of about one-sixth of the human genome. It has non-genomic actions in protein translation and paracrine actions. Retinal vitamin A aldehyde is crucial for day and night vision. The best-known manifestation of hypovitaminosis A is night blindness but in more severe cases, it causes blindness. In the hypothalamus, vitamin A, with information from the retina, acts in circadian and seasonal regulation. Increased retinoic acid levels in the blood are associated with increased risk of depression, and lower levels have been connected with Alzheimer's disease, Parkinson's disease, cerebral ischemia, autistic spectrum disorders and schizophrenia. Higher doses and longer periods of treatment pose the threat of hypervitaminosis A. Vitamin A and its analogs are a promising new class of therapeutic agents in a wide spectrum of disorders, albeit with a narrow therapeutic window.