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Use of a short-term isotope-dilution method for determining the vitamin A status of children
Guangwen Tang1, Jian Qin, Lan-ying Hao
1Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA. gtang@hnrc.tufts.edu
Insights
Vitamin A body stores can be accurately estimated using blood samples collected after 3 days, simplifying field assessments. This 3-day measurement correlates well with traditional 21-day assessments for vitamin A status.
Area of Science:
- Human Nutrition
- Biochemistry
- Public Health
Background:
- Estimating vitamin A body stores typically requires blood collection 11-26 days after administration of a labeled dose.
- Current methods are time-consuming and less practical for field settings.
Purpose of the Study:
- To determine if shorter blood collection intervals (6 hours or 3 days) are feasible for estimating vitamin A body stores.
- To develop a more practical method for assessing vitamin A status in human populations.
Main Methods:
- Deuterium-labeled vitamin A was administered orally to Chinese schoolchildren (n=58, aged 10-11 years) with marginal-to-normal vitamin A status.
- Blood enrichment was measured at 6 hours, 3 days, and 21 days.
- A predictive equation was developed using 3-day enrichment data to estimate 21-day enrichment.
Main Results:
- A strong correlation was observed between 3-day and 21-day isotope enrichment.
- The predictive equation accurately estimated 21-day enrichment using 3-day data.
- Vitamin A body stores calculated using predicted and directly measured 21-day enrichment showed agreement.
Conclusions:
- Blood enrichment at 3 days post-dose is a reliable indicator for evaluating human vitamin A body stores.
- A 6-hour collection interval was not sufficient for accurate estimation.
- This 3-day method offers a more practical approach for field-based vitamin A assessments.
Background:
After a dose of labeled vitamin A is given to humans for estimating body stores of vitamin A, blood is customarily drawn at pseudo-equilibration times ranging from 11 to 26 d.
Objective:
The objective was to determine whether a shorter sample collection interval (6 h or 3 d), which would be more realistic in field settings, can be used.
Design:
Correlations of enrichment at 6 h or 3 d with enrichment at 21 d were made after an oral dose of deuterium-labeled vitamin A was given to Chinese schoolchildren (aged 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 to verify that the calculated enrichment at 21 d (determined by using data obtained at an earlier time point to predict 21-d enrichment) reflected directly measured enrichment at 21 d.
Results:
Because 3-d isotope enrichment was found to correlate well with 21-d enrichment, a predictive equation was derived whereby 3-d data were used to predict isotope enrichment at pseudo-equilibration (ie, at 21 d). When the 3-d predictive equation was applied to a separate group of Chinese children, the calculated 21-d data (determined by using the 3-d data and the predictive equation) matched the directly measured 21-d data. Body stores of vitamin A determined from either the calculated or directly measured 21-d enrichment data also showed agreement.
Conclusion:
Percentage enrichment at 3 d (but not at 6 h) can be used to evaluate vitamin A body stores in humans.