Vitamin A deficiency
Vitamin A is a collection of fat soluble retinoids (retinal, retinol and retinyl esters) that are involved in immunity, cell growth & differentiation and communication, vision and reproduction. Human takes 2 types of vitamin A, which are preformed vitamin A and provitamin A / carotenoids (alpha & beta carotene and beta cryptoxanthin) that are metabolized intracellularly into active vitamin A [1]. 50-80% vitamin A are cellular RBP (retinol binding protein) / tranthyretin bound in liver and the rest is deposited into kidneys, lungs and adipose tissue as retinyl palmitate [2].
Vitamin A deficiency (VAD) / hypovitaminosis is very common in Africa and South Asia and according to WHO around 2500000 to 5000000 children become blind every year due to VAD among which half of them die within a year after blindness. Pregnant women are also at higher risk for vitamin A deficiency during third trimester. Patients with cystic fibrosis, cancer, pancreatic insufficiency, inflammatory bowel disorder (IBD) are also at increased risk for VAD. The serum retinol concentration is affected by several factors such as infection, RBP synthesis in liver and zinc & iron levels. While zinc deficiency affects retinol transport from liver, iron deficiency affects vitamin A metabolism.
Vitamin A has huge impact on vision so VAD results in various types of vision problem including xeropthalmia, night blindness, corneal inflammation, keratomalacia, corneal xerosis, bitot’s spots (abnormal squamous cell proliferation and keratinization of conjunctiva that results in irregular foamy patches in the white of the eye) etc. Xeropthalmia is characterized by abnormal dryness of cornea and conjunctiva that leads to cessation of lachrymal fluid / tears that results in thick, dehydrated and wrinkled conjunctiva. Keratomalacia is characterized by xerosis and dryness with ulceration and perforation in the cornea that results in eye loss. As retinol plays an important role in rhodopsin (which is a photoreceptor pigment essential to the retinol receptors that are responsible for night vision) formation, VAD also results in night blindness [3].
Recently researchers from Weill Cornell medical college found that VAD may lead to beta cell loss in pancreas that results in reduced insulin production and increased blood glucose levels which are main symptoms of type 2 diabetes [4].
Chicken, egg, whole milk, carrot, orange color fruits, sweet potatoes, spinach, kale and green vegetables are rich in vitamin A and daily 5 servings of these vitamin A rich food should be taken to avoid or reduce VAD. In high risk population mainly in children from 6 months to 5 years, vitamin A supplementation is recommended to reduce morbidity, mortality and blindness.
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