Using Stable Isotope Techniques to Monitor & Assess the Vitamin A Status of Children Susceptible to Infection

Overview

The relationship between infections and malnutrition is synergistic, each further compromising the outcome of the other. Malnutrition compromises natural immunity leading to increased susceptibility to infections, more frequent and prolonged disease episodes, and increased severity of disease. Likewise, infections can aggravate or precipitate malnutrition through decreased appetite and food intake, nutrient malabsorption, nutrient loss or increased metabolic needs. Severe malnutrition often masks symptoms and signs of infectious diseases making prompt clinical diagnosis and treatment very difficult. Another issue is that infections (as well as overweight and obesity status) affect nutritional biomarkers making it difficult to assess the real magnitude of some nutritional problems. This is the case of vitamin A. Vitamin A deficiency is defined to be of severe public health importance if 20% or more of a defined population has a serum retinol concentration of less than 0.7 µmol/L.

Vitamin A is an essential nutrient needed for the visual system, and maintenance of cell function for growth, epithelial integrity, red blood cell production, immunity and reproduction. All infants are born with low stores and depend on vitamin A from breast milk to initially accumulate and maintain adequate stores. Infants of vitamin A depleted women are at greater risk of becoming vitamin A deficient early in life, especially if they are not breast fed. Correcting vitamin A deficiency is addressed by some African countries through vitamin A supplementation of children and food fortification programs. However, assessing vitamin A status, and the effectiveness of government interventions, is challenging in settings where infectious diseases are endemic, as in most African countries. Evaluation of vitamin A status is relatively insensitive when based on changes in serum retinol concentrations, which are homeostatically controlled and negatively affected by subclinical infections. Liver stores of vitamin A, the best indicator of vitamin A status, cannot be routinely evaluated. The isotope dilution technique is the preferred method for determining vitamin A status and assessing the efficacy and effectiveness of intervention programs aimed at improving vitamin A status. It is the only indirect assessment method that provides a quantitative estimate of vitamin A status across the continuum of deficient to excessive stores. Thus, this technique can be used for assessing vitamin A status in populations at risk of excessive status due to exposure to too much vitamin A through combined supplementation and consumption of fortified foods and/or preformed vitamin A-rich foods. The aim of this project is to use nuclear techniques to evaluate vitamin A nutritional status of young children during semi-annual administration of vitamin A supplements, and to assess how this relates to infection status. The IAEA has provided significant support on use of stable isotopes in assessing body composition and breast milk to Member States in Africa, it is now establishing the stable isotope technique to assess vitamin A body stores in Cameroon and Zambia (and additional implementation is possible in Morocco) for use throughout the region. These inputs will be used in this project to provide key information to stakeholders on how vitamin A intervention programs affect vitamin A status in children and how infections affect vitamin A status or validity of stable isotope techniques.