A test to measure oral iron absorption and glucose tolerance simultaneously in 18 to 55 year old premenopausal women

BACKGROUND & AIMS

Several methods are available to measure iron absorption (IA). The oral iron absorption test (OIAT) measures IA based on a change in serum iron (ΔSeFe) concentration after an oral iron dose. The objective of this study was to validate the OIAT by comparing it to the reference method of fractional iron absorption (FIA) using red blood cell incorporation of stable iron isotopes from a labeled iron dose. A second objective was to assess whether the OIAT could be done simultaneously with an oral glucose tolerance test (OGTT), since iron deficiency and glucose intolerance may coexist, especially among overweight individuals with low-grade inflammation.

METHODS

In this prospective experimental study, 116 women were enrolled and IA was measured using two different approaches 1) FIA from a labeled test meal containing 6 mg of ⁵⁷Fe and 2) the OIAT assessing ΔSeFe at 2 h after the intake of 100 mg oral iron, done simultaneously with an OGTT. Markers of iron status, glycaemia and inflammation, and serum hepcidin, were measured.

RESULTS

Prevalence of anemia and iron deficiency (defined as low serum ferritin) were 21% and 14%, respectively. ΔSeFe during the OIAT-OGTT was positively associated with FIA (r = 0.578, p < 0.001). ΔSeFe was not significantly correlated with markers of glucose and insulin metabolism during the OIAT-OGTT.

CONCLUSIONS

The combined OIAT and OGTT method described here correlates well with FIA measured by stable iron isotopes, and could provide information on both IA and glucose tolerance in a single 2-h test, decreasing the burden on patients. clinicaltrials.gov (NCT03642223).

Non-Heme Iron Absorption and Utilization from Typical Whole Chinese Diets in Young Chinese Urban Men Measured by a Double-Labeled Stable Isotope Technique

BACKGROUND

This study was to observe the non-heme iron absorption and biological utilization from typical whole Chinese diets in young Chinese healthy urban men, and to observe if the iron absorption and utilization could be affected by the staple food patterns of Southern and Northern China.

MATERIALS AND METHODS

Twenty-two young urban men aged 18-24 years were recruited and randomly assigned to two groups in which the staple food was rice and steamed buns, respectively. Each subject received 3 meals containing approximately 3.25 mg stable 57FeSO4 (the ratio of 57Fe content in breakfast, lunch and dinner was 1:2:2) daily for 2 consecutive days. In addition, approximately 2.4 mg 58FeSO4 was administered intravenously to each subject at 30-60 min after dinner each day. Blood samples were collected from each subject to measure the enrichment of the 57Fe and 58Fe. Fourteen days after the experimental diet, non-heme iron absorption was assessed by measuring 57Fe incorporation into red blood cells, and absorbed iron utilization was determined according to the red blood cell incorporation of intravenously infused 58Fe SO4.

RESULTS

Non-heme iron intake values overall, and in the rice and steamed buns groups were 12.8 ±2.1, 11.3±1.3 and 14.3±1.5 mg, respectively; the mean 57Fe absorption rates were 11±7%, 13±7%, and 8±4%, respectively; and the mean infused 58Fe utilization rates were 85±8%, 84±6%, and 85±10%, respectively. There was no significantly difference in the iron intakes, and 57Fe absorption and infused 58Fe utilization rates between rice and steamed buns groups (all P>0.05).

CONCLUSION

We present the non-heme iron absorption and utilization rates from typical whole Chinese diets among young Chinese healthy urban men, which was not affected by the representative staple food patterns of Southern and Northern China. This study will provide a basis for the setting of Chinese iron DRIs.

Novel and nontraditional use of stable isotope tracers to study metal bioavailability from natural particles

We devised a novel tracing approach that involves enriching test organisms with a stable metal isotope of low natural abundance prior to characterizing metal bioavailability from natural inorganic particles. In addition to circumventing uncertainties associated with labeling natural particles and distinguishing background metals, the proposed "reverse labeling" technique overcomes many drawbacks inherent to using radioisotope tracers. Specifically, we chronically exposed freshwater snails ( Lymnaea stagnalis ) to synthetic water spiked with Cu that was 99.4% (65)Cu to increase the relative abundance of (65)Cu in the snail's tissues from ~32% to >80%. The isotopically enriched snails were then exposed to benthic algae mixed with Cu-bearing Fe-Al particles collected from the Animas River (Colorado), an acid mine drainage impacted river. We used (63)Cu to trace Cu uptake from the natural particles and inferred their bioavailability from calculation of Cu assimilation into tissues. Cu assimilation from these particles was 44%, indicating that 44% of the particulate Cu was absorbed by the invertebrate. This demonstrates that inorganic particulate Cu can be bioavailable. The reverse labeling approach shows great potential in various scientific areas such as environmental contamination and nutrition for addressing questions involving uptake of an element that naturally has multiple isotopes.

Use of stable isotopes to assess the bioavailability of trace elements: a review

The bioavailability (utilization) of trace elements is very variable, depending on the characteristics of the element itself, composition of the diet, gastrointestinal conditions and other physiological factors. To derive dietary recommendations and make use of emerging information on diet-gene interactions relating to nutritional requirements for trace elements, methods for assessing bioavailability are required. The trace elements of particular interest include iron, zinc, selenium and copper because of problems of deficiency, purported links with chronic diseases, and the growing market in fortified foods and supplements. The absorption and subsequent metabolism of trace elements can be monitored using stable isotope tracers, but there are difficulties associated with this approach. Although radioisotopes offer many advantages over stable isotopes, their use is restricted due to safety and ethical issues. The difficulties and limitations of methodologies associated with labelling of trace elements in foods with stable isotopes, design of human studies to generate results that predict bioavailability, and detection and quantification of stable isotopes in biological samples are discussed.

Iron

The most useful and appropriate methods for assessing the bioavailability of (nonheme) iron supplements are described. When the supplement can be labeled isotopically, the best method for measuring bioavailability is hemoglobin incorporation, followed by fecal monitoring. Caco-2 cell in vitro systems can be used for rapid screening to predict potential availability for absorption. If the compound cannot be labeled, then the plasma appearance/disappearance of oral iron given together with an intravenous dose of iron isotope can be used to quantify absorption. With oral doses in excess of 25 mg, the 4- to 6-h plasma concentration can provide a qualitative assessment of bioavailability. Approaches for normalizing results to minimize intraindividual and interindividual variability in efficiency of iron absorption are discussed.