Author
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Turnlund, Judith |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/25/2005 Publication Date: 1/1/2006 Citation: Turnlund, J.R. Mineral bioavailability and metabolism determined by using stable isotope tracers. 2006. Journal of Animal Science. J. Anim. Sci. 84(E Suppl.)E73-E79. Interpretive Summary: Stable isotopes are valuable tools for studies of mineral metabolism in humans. When minerals in the diet are consumed they enter the gastrointestinal tract. Varying fractions of the amounts consumed are absorbed and enter into systemic circulation. They mix with minerals consumed earlier and are deposited in various organs and tissues in the body. Fractions of the absorbed minerals are excreted along with endogenous minerals via bile and pancreatic secretions into the gastrointestinal tract. There they mix with unabsorbed dietary minerals. Fractions are also excreted via the urine and other miscellaneous routes. Stable isotopes of a mineral occur in nature in fixed abundances. The isotopes can be separated electromagnetically and collected. Isotopes of low abundances can be used as tracers to follow the metabolic fate of minerals in a specific diet or dose and to separate them from endogenous minerals and those consumed at other times. Technical Abstract: Definitive data on mineral bioavailability in humans and animals can be obtained by using isotopic tracers. The use of stable isotope tracers to study important issues in mineral nutrition has expanded rapidly in the past two decades, particularly in humans. Stable isotopes have a number of advantages over radioisotopes. There is no exposure to radiation with stable isotopes and some minerals have no radioisotope that can be used satisfactorily as a tracer. Multiple stable isotopes of one mineral and isotopes of multiple minerals can be administered simultaneously or sequentially. The analytical methods of choice for stable isotopes are thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICPMS). TIMS offers the highest precision and accuracy, but is slower, more labor intensive, and more costly than ICPMS. Bioavailability data are critical to establishing reliable dietary mineral requirements and recommendations. Combined with a computer program for compartmental modeling, mineral kinetics can be studied, including mineral turnover, pool sizes, and transfer rates between compartments. Our laboratory conducts studies using stable isotopes of zinc, copper, iron, calcium, magnesium, and molybdenum. We have studied the effect of the amount of dietary intake of minerals on bioavailability and utilization, pregnancy and aging, and interactions between minerals. The work resulted in establishing new dietary recommendations in humans for copper and molybdenum and compartmental models were developed for these minerals. While stable isotopes have been used more extensively to date in humans than in animals, the techniques applied to humans can be used to study a number of issues important to optimizing feeding strategies for animal production. |
