Stable isotope dilution techniques for assessing vitamin A status and bioefficacy of provitamin A carotenoids in humans

Abstract

Vitamin A deficiency is a major global public health problem. Among the variety of techniques that are available for assessing human vitamin A status, evaluating the provitamin A nutritional values of foodstuffs and estimating human vitamin A requirements, isotope dilution provides the most accurate estimates. Although the relative expense of isotope dilution restricts its applications, it has an important function as the standard of reference for other techniques. Mathematical modelling plays an indispensable role in the interpretation of isotope dilution data. This review summarises recent applications of stable isotope methodology to determine human vitamin A status, estimate human vitamin A requirements, and calculate the bioconversion and bioefficacy of food carotenoids.

Evaluation of the “Olson Equation”, an Isotope Dilution Method for Estimating Vitamin A Stores

“…Furr et al [2] addressed some of these problems with the equation proposed in 1989 (Eqn [1]). Specifi cally, they introduced the factor F (fraction of the dose absorbed and retained in stores at the time of sampling) and assigned it a value of 0.5 based on the work of Rietz et al discussed above (Fig.…”

“…Since then, this "Olson equation" or "deuterated retinol dilution (DRD) equation" has been fruitfully used to estimate stores or to evaluate interventions in a number of human studies (for example, see references [3 -5]). More details on the development and application of the retinol isotope dilution (RID) method have been presented by Furr et al [1] and Haskell et al [6]. …”

“…Eqn [1] where TLR = total liver vitamin A; F = fraction of an orally administered isotopic dose that is absorbed and retained; S = ratio of specifi c activity of retinol in plasma to that in liver after equilibration; a = correction for fraction of dose lost via catabolism; H :D = postequilibration hydrogen-to-deuterium ratio in plasma retinol after administration of the oral dose of deuterated vitamin A; and -1 = correction for the contribution of the dose to vitamin A stores. The theoretical basis of the isotope dilution technique rests on the fact that, following administration of a tracer dose of labeled vitamin A to a subject who is not consuming vitamin A, the specifi c activity of vitamin A in plasma will be equal to that in the exchangeable storage pools once the dose has mixed with these pools.…”

“…As reviewed by Furr et al [1], many methods have been proposed for estimating vitamin A status. Among the most actively investigated and potentially most useful are isotope dilution techniques which provide an indirect estimate of total body stores of vitamin A.…”

Conceptualizing dietary Westernization, observing dietary transitions

“…Certainly, social, economic and cultural changes lie at the heart of the process of dietary Westernisation. However, not atypically for our journal, the papers contained within the present regular issue also represent a sampling of topics falling at different corners of the new nutrition science -a review of isotope dilution techniques to assess vitamin A status 7 , the association of geographic area deprivation with childhood obesity 8 and the contribution of drought in southern Africa to childhood malnutrition 9 . We look forward to discussions and to the development of a new conceptual framework to organise the scope of work falling within nutritional science, and to take our discipline to new directions 10 .…”