Insights into human brain: Vitamin A in neuropsychiatry and ophtalmology

Abstract

Vitamin A is a liposoluble vitamin essential for brain function and vision, and is obtained only through food as retinol or as carotenoids. The active metabolite is retinoic acid (RA), which participates in cognitive processes in the hippocampus, particularly in learning and spatial functions as well as in neurogenesis. Retinoic acid is essential for the vision and the maintenance of the cornea, biological rhythms, mucosa defense against infections and regulation of many genes (one sixth of the human genome). In animal models, vitamin A deficiency shows changes that resemble neurodegeneration, and RA levels in the plasma and cerebrospinal fluid of patients with Alzheimer's disease are reduced. There is also a complex relationship between RA and affective disorders, schizophrenia, autism, Parkinson's disease and stroke. In developing countries hypovitaminosis A is one of the leading causes of death and blindness in children, while in developed countries the symptoms are less noticeable. The damage of the cornea and night blindness are the consequences of hypovitaminosis, and there is a possible association of RA and glaucoma, macular degeneration and other eye diseases. A variety of infections can occur and can be deadly. The most efficient use of vitamin A is in the prophylactic purposes in the population at risk, especially pregnant women and infants in developing countries, while the results in the treatment of neurodegenerative and psychiatric diseases are controversial. Excessive doses of vitamin A can lead to hypervitaminosis with bone, gastrointestinal, psychiatric and neurological manifestations. New studies should demonstrate the most appropriate place of vitamin A in the treatment of neuropsychiatric diseases.

Vitamin A je liposolubilni vitamin neophodan za rad mozga i za vid, a unosi se isključivo putem hrane kao retinol ili u vidu karotenoida. Aktivni metabolit je retinočka kiselina (RA) koja učestvuje u kognitivnim procesima u hipokampusu, naročito u učenju i specijalnim funkcijama i neurogenezi u hipotalamusu. Retiočna kiselina je neophodna za vid, održavanje kornee, za biološke ritmove, odbranu sluznica od infekcija i regulaciju mnogih gena (šestina humanog genoma). U animalnim modelima nedostatak vitamina A daje promene koje liče na neurodegeneraciju, a nivo retinoičke kiseline u plazmi i cerebrospinalnoj tečnosti obolelih od Alchajmerove bolesti je snižen. Takođe postoji složena veza RA i afektivnih poremećaja, shizofrenije, autizma, Parkinsonove bolesti i moždanog udara. U nerazvijenim zemljama je hipovitaminoza A jedan od vodećih uzroka smrtnosti i slepila kod dece, dok su u razvijenijim zemljama simptomi manje uočljivi. Nastaje oštećenje kornee, noćno slepilo, a moguć je udeo RA i u glaukomu, makularnoj degeneraciji kao i drugim očnim bolestima. Nastupaju razne infekcije koje mogu biti i smrtonosne. Najefikasnija primena vitamina A je u profilaktičke svrhe kod stanovništva u riziku, posebno trudnica i odojčadi u nerazvijenim zemljama, dok su rezultati u lečenju neurodegenerativnih i psihijatrijskih bolesti kontroverzni. Preterane doze vitamina A mogu da dovedu do hipervitaminoze sa koštanim, gastrointestinalnim, psihijatrijskim i neurološkim ispoljavanjima. Nove studije treba da pokažu najadekvatnije mesto vitamina A u terapiji neuropsihijatrijskih bolesti.