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Title: Current capabilities and limitations of the stable isotope technologies and applied mathematical equations in determining whole body vitamin A status

Author
item LIETZ, GEORG - Newcastle University
item FURR, HAROLD - University Of Wisconsin
item GANNON, BRYAN - University Of Wisconsin
item GREEN, MICHAEL - Pennsylvania State University
item HASKELL, MARJORIE - University Of California
item LOPEZ-TEROS, VERONICA - Universidad De Sonora
item Novotny, Janet
item PALMER, AMANDA - Johns Hopkins University
item RUSSELL, ROBERT - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item TANUMIHARDJO, SHERRY - University Of Wisconsin

Submitted to: Food and Nutrition Bulletin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2016
Publication Date: 4/6/2016
Citation: Lietz, G., Furr, H., Gannon, B., Green, M., Haskell, M., Lopez-Teros, V., Novotny, J.A., Palmer, A., Russell, R., Tanumihardjo, S. 2016. Current capabilities and limitations of the stable isotope technologies and applied mathematical equations in determining whole body vitamin A status. Food and Nutrition Bulletin. 37:S87-S103.

Interpretive Summary: Vitamin A (VA) deficiency remains one of the most significant nutritional problems worldwide. One difficulty in assessing the effectiveness of interventions to ameliorate VA deficiency is that there is no simple test to determine VA status. Thus, it is difficult to determine if food or supplement based programs are improving VA status of target populations. This manuscript discusses currently available methods for determining VA status and the pitfalls of those methods. The methods involve administration of tagged (i.e., isotope labeled) VA to individuals, then collection of blood to determine how much the tagged VA was diluted in the body pool. Different mathematical formulas are available for translating the measured dilution value to values for VA stores, and the proper timing of blood collection and the specific mathematical equation are not generally agreed upon. At present, there is insufficient information on absorption of the tagged VA, and there is a need to investigate further how various factors impact application of the technique in field studies. Current methodologies can provide estimates of total body VA stores in apparently healthy populations under controlled study conditions, but more research is needed to determine whether the method is suitable for use in settings where there is a high prevalence of factors that influence VA movement in the body, such as infection, iron deficiency, and/or liver disease. A more completed understanding of the methods used to determine VA status are critical for public health professionals, food aid programs and scientists who are working to ameliorate the global VA deficiency problem.

Technical Abstract: Vitamin A (VA) stable isotope dilution methodology provides a quantitative estimate of total body VA stores and is the best method currently available for assessing VA status in adults and children. The methodology has also been used to test the efficacy of VA interventions in a number of low-income countries. Many factors, including infections, micronutrient deficiencies such as iron and zinc deficiencies, liver disease, physiological age, pregnancy, and lactation, are known or hypothesized to influence the accuracy of estimating total body VA stores using the isotope dilution technique. Our objectives were to review the strengths and limitations of stable isotope dilution methods, to discuss what is known about the impact of various factors on results, and to summarize contributions of model-based compartmental analysis to assessing VA status. Relevant published literature is reviewed and discussed. Various equations and compartmental modelling have been used to estimate total body VA stores using stable isotopes, including a newer 3-day equation that provides an estimate of total body VA stores in healthy adults. At present, there is insufficient information on absorption of the isotope tracer, and there is a need to investigate further how various factors impact application of the technique in field studies. Isotope dilution methodology can provide useful estimates of total body VA stores in apparently healthy populations under controlled study conditions. However, more research is needed to determine whether the method is suitable for use in settings where there is a high prevalence of infection, iron deficiency, and/or liver disease.