10 March 2010
Vitamin A may play a critical role in production of energy in our cells, says new research.
01 February 2016
A new pooled analysis of population surveys has shown that vitamin A deficiency among children in 138 low- and middle-income countries has fallen by slightly over one quarter in 22 years between 1991 and 2013.
A sufficient vitamin A (retinol) intake is essential for the process of vision (especially night vision) and for immune function, where it helps to protect against infections by ensuring the effectiveness of mechanical barriers (e.g., skin), and increasing the production and efficacy of protective cells (e.g., lymphocytes).
Deficiency can cause eye diseases such as xerophthalmia, which may progress to permanent blindness (2). In children, deficiency can lead to an increase in the risk of infection, specifically there is an increased risk of death from measles and diarrhea (3).
The Institute of Medicine in the USA recommends daily doses of vitamin A (at retinol equivalents) of 300 μg, 400 μg and 500 μg for children aged 1 to 3 years, 4 to 8 years and 9 to 13 years respectively. In 1997, UNICEF and the World Health Organization launched a global campaign to distribute vitamin A capsules to children suffering from malnutrition. In 2002, the International Vitamin A Consultative Group (IVACG) signed the Annecy Accord which involved collaboration with international organizations to develop and establish guidelines for the diagnosis, treatment and prevention of vitamin A deficiency disorders (4).
Vitamin A deficiency frequently causes night blindness in deprived children in the developing world. If this is not rectified, it can lead to corneal scarring and eventually total blindness. It is believed that around one quarter of sub-Saharan African children are at risk. There is the challenge of being able to identify children at risk before commencing vitamin A supplementation. Alain Labrique and colleagues at Johns Hopkins Bloomberg School of Public Health have developed a piece of low cost, robust apparatus able to do this called the Portable Dark Field Adaptometer (PDFA). This lightweight, head-mounted unit measures the pupillary response to light stimulus. The PDFA has been successfully trialed in the field in Bangladesh, Kenya, Zambia and Peru as a means of detecting the initial signs of vitamin A deficiency (5).
An alternative to using capsules to treat vitamin A deficiency in Africa is to encourage the planting of crops used in staple foods that are naturally high in vitamin A. A good example are the orange-fleshed varieties of the sweet potato, which are rich in beta-carotene (a precursor of vitamin A). In recent years, there have been several large scale intervention programs to introduce the orange-fleshed sweet potato to rural communities in Mozambique and Uganda (6). However, there are some limitations as to the usefulness of this approach because the crop is seasonal, but if a judicious planting cycle is used, it can provide orange-fleshed sweet potato for nine to ten months of the year. In the Eastern Cape of South Africa, local communities were encouraged and assisted with growing beta-carotene-rich crops in their vegetable gardens (e.g., butternut squash, carrot, spinach and orange-fleshed sweet potato). After three years, it was shown to have a favorable effect with regard to reducing child mortality.
Stevens et al. (1) assessed serum retinol concentration data of young children from 134 population-representative data sources from 83 countries. Vitamin A deficiency was defined as a serum retinol concentration lower than 0.7 μmol/L. They found that in 1991, 39% of children aged 6 to 59 months in low- and middle-income countries were deficient. By 2013, the levels of deficiency had reduced by around one quarter to around 29%. Regionally, in 2013, vitamin A deficiency was highest in sub-Saharan Africa at 48% and in South Asia at 44%. These regions also accounted for 95% of the deaths of children under five due to diarrhea and measles caused by vitamin A deficiency. Overall, vitamin A deficiency was responsible for 1.7% of deaths of all children aged under five years in 2013. Only in East Asia, South East Asia and Oceania was there a significant decrease in vitamin A deficiency. Here the prevalence of vitamin A deficiency dropped from 42% in 1991 to just 6% in 2013.