USE OF A SHORT ISOTOPE DILUTION METHOD FOR DETERMINING VITAMIN A STATUS OF CHILDREN

Authors: TANG, GUANGWEN - HNRCA; QIN, JIAN - IBID; HAI, LANYING - SHUN-YI DISTRICT HEALTH &; YIN, SHI-AN - INST OF NUTR & FOOD HYG; RUSSELL, ROBERT - HNRCA

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2001
Publication Date: 8/1/2002
Citation: TANG, G., QIN, J., HAI, L., YIN, S., RUSSELL, R.M. USE OF A SHORT ISOTOPE DILUTION METHOD FOR DETERMINING VITAMIN A STATUS OF CHILDREN.. AMERICAN JOURNAL OF CLINICAL NUTRITION. 2002;76(2):413-8.

Interpretive Summary: Vitamin A deficiency affects 75 to 140 million children in developing countries. In the past, vitamin A status has been evaluated using dietary assessment tools, functional tests (such as testing for night blindness), biochemical methods, and isotope dilution techniques that measure the dilution of labeled vitamin A in the circulation after given an oral dose of labeled vitamin A. When using isotope dilution techniques to determine body stores of vitamin A, blood samples are characteristically collected at post test-dose times ranging from 11-26 days. During this long waiting period, various factors such as infection, fever, or sickness in the study population can affect the degree of isotope dilution, and thereby interfere with the determination of vitamin A body stores. This prompted us to test whether a shorter sample collection interval (6 hours or 3 days) could be used. Correlations of isotope dilution at 6 hours or 3 days with that of 21 days were made after giving an oral dose of deuterium labeled vitamin A to 58 Chinese school children (aged 10 11 years) with marginal to normal vitamin A status. A predictive 3 day equation was derived from this study. When this equation was applied to a separate group of Chinese children, the calculated dilutions showed excellent agreement with the dilutions that were actually measured. These observations provide evidence that 3 day isotope dilution measurements can be used to calculate vitamin A body stores in humans.

Technical Abstract: After giving a labeled vitamin A dose to humans to estimate body stores of vitamin A, blood customarily has been drawn at pseudo equilibration times ranging from 11-d to 26-d.To determine whether a shorter sample collection interval (6-h or 3-d) can be used which would be more realistic to employ in field settings. Correlations of enrichment at 6-h or 3-d with enrichment at 21-d were made after giving an oral dose of deuterium labeled vitamin A to Chinese school children (10 11 y n = 58) with marginal to normal vitamin A status. A predictive equation was then derived and applied to data obtained from a separate group of children in order to verify that the calculated enrichment at 21-d (using measured early time point data to obtain a predicted 21-d enrichment) reflects directly measured enrichment at 21-d. Since 3-d isotope enrichment was found to correlate well with 21-d enrichment, a predictive equation was derived whereby 3-d data was used to predict isotope enrichment at pseudo equilibration (i.e. at 21-d). When the 3-d predictive equation was applied to a separate group of Chinese children, the calculated 21-d data (using the 3-d data and the predictive equation) matched the directly measured 21-d data. Derived body stores of vitamin A using either the calculated or directly measured 21-d enrichment data also showed agreement. These observations provide evidence that it is possible to use percentage enrichment at 3-d (but not at 6-h) to evaluate vitamin A body stores in humans.