As an oral form, the supplementation of vitamin A is effective for lowering the risk of morbidity, especially from severe diarrhea, and reducing mortality from measles and all-cause mortality. Vitamin A supplementation of children under five who are at risk of VAD can reduce all‐cause mortality by 23%. Some countries where VAD is a public-health problem address its elimination by including vitamin A supplements available in capsule form with national immunization days (NIDs) for polio eradication or measles. Additionally, the delivery of vitamin A supplements, during integrated child health events such as child health days, have helped ensure high coverage of vitamin A supplementation in a large number of least developed countries. Child health events enable many countries in West and Central Africa to achieve over 80% coverage of vitamin A supplementation. According to UNICEF data, in 2013 worldwide, 65% of children between the ages of 6 and 59 months were fully protected with two high-dose vitamin A supplements. Vitamin A capsules cost about US$0.02. The capsules are easy to handle; they do not need to be stored in a refrigerator or vaccine carrier. When the correct dosage is given, vitamin A is safe and has no negative effect on seroconversion rates for oral polio or measles vaccines. However, because the benefit of vitamin A supplements is transient, children need them regularly every four to six months.
Intramuscular injections are poorly absorbed and are ineffective in delivering sufficient bioavailable vitamin A. Fortification of food with vitamin A is costly, but can be done in wheat, sugar, and milk. Households may circumvent expensive fortified food by altering dietary habits. Consumption of yellow-orange fruits and vegetables rich in carotenoids, specifically beta-carotene, provides provitamin A precursors that can prevent VAD-related night blindness. However, the conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies. Infection
Along with poor diet, infection and disease are common in many developing communities. Infection depletes vitamin A reserves which in turn make the affected individual more susceptible to further infection. Increased incidence of xerophthalmia has been observed after an outbreak of measles, with mortality correlated with severity of eye disease. In longitudinal studies of preschool children, susceptibility to disease increased substantially when severe VAD was present.The reason for the increased infection rate in vitamin A deficient individuals is that T-killer cells require the retinol metabolite retinoic acid to proliferate correctly. Retinoic acid is a ligand for nuclear retinoic acid receptors that bind the promoter regions of specific genes, thus activating transcription and stimulating T cell replication. Vitamin A deficiency will often entail deficient retinol intake, resulting in a reduced number of T-cells and lymphocytes, leading to an inadequate immune response and consequently a greater susceptibility to infections. In the presence of dietary deficiency of vitamin A, VAD and infections reciprocally aggravate each other. Causes
In addition to dietary problems, other causes of VAD are known.