Dr. Muhammad Torequl Islam :
Vitamin A, a group of unsaturated nutritional organic compounds that includes retinol, retinal, retinoic acid and several provitamin A carotenoids (e.g., beta-carotene). It is important for growth and development, for the maintenance of the immune system, and for good vision. Deficiency of this vitamin is estimated to affect more than 33% of children under 5 years worldwide. Its deficiency is the leading cause of preventable childhood blindness.
A primary vitamin A deficiency occurs due to inadequate intake of provitamin A carotenoids from fruits and vegetables or preformed vitamin A from animal, dairy products and an early weaning from breast milk. On the other hand, a secondary vitamin A deficiency is associated with the chronic malabsorption of lipids, impaired bile production and release, and chronic exposure to oxidants (e.g., cigarette smoke, chronic alcoholism). Low-fat-diets and zinc deficiency also result vitamin A deficiency. Besides night-blindness, it’s deficiency also link to xerophthalmia (eye fails to produce tears), impaired immunity (increased risk of ear infections, urinary tract infections, meningococcal disease), hyperkeratosis (white lumps at hair follicles), keratosis pilaris, squamous metaplasia of the epithelium lining the upper respiratory passages and urinary bladder to a keratinized epithelium, and enamel hypoplasia.
Retinyl palmitate is used in skin creams, while its derivatives retinol and retinoic acid have been reported to have diverse biological activities, including antioxidant, anti-inflammatory, anti-viral and anti-cancer effects. Megadoses of naturally occurring retinoic acid derivatives have been used in cancer, human immunodeficiency virus (HIV) and dermatological purposes.
An adequate vitamin A intake is required in early lung development, alveolar formation, tissue maintenance and regeneration. Chronic deficiency of this vitamin has been found to cause histopathological changes in the pulmonary epithelial lining that disrupt the normal lung physiology predisposing to severe tissue dysfunction and respiratory diseases. It also causes an important alteration of the structure and composition of extracellular matrix with thickening of the alveolar basement membrane and ectopic deposition of collagen I. Moreover, during oxidation, an addition of oxygen to low-density lipoproteins, contributes to the build up of fatty plaque on artery walls (atherosclerosis), which can eventually slow or block blood flow to the heart. Retinol, retinotic acid, retinyl palmitate and beta-carotene are evident to act significantly against oxidative stress.
Vitamin A as well as retinoids were also found to inhibit measles virus replication by upregulating the elements of innate immune response in uninfected bystander cells, thereby inhibiting viral replication. To date, in novel coronavirus disease 2019 (COVID-19) a phase IV clinical trial (King Saud University) on 30 patients has been undergone on the beta-carotene along with other supplements. Therefore, correction of vitamin A deficiency during the pandemic COVID-19 should be taken into account.
(Dr. Muhammad Torequl Islam is Assistant Professor,
Department of Pharmacy, Life Science Faculty, Bangabandhu Sheikh Mujibur Rahman Science and Technology University.
E-mail: [email protected])
