Using stable isotopes and isotope ratio mass spectrometry to study mineral metabolism in humans

Micronutrient deficiencies are enormous problems globally. Iron deficiency alone may affect 2 billion people, of whom at least 500 million are anaemic. Stable isotopes provide many methods to study mineral metabolism in humans. These range from relatively simple measurements of absorption, and endogenous faecal excretion, to complex studies using multi-compartmental modelling. Most studies use highly enriched stable isotope tracers administered intravenously and/or orally, coupled with precise measurements of the resulting isotopic enrichment in blood, urine or faeces. Stable isotope methodologies are becoming much more widely utilised due to the decreasing cost of isotopes and increasing acceptance of these methods. Two factors that have hampered broader use of stable isotope-based methods are the cost and limited availability of analytical methods that can measure isotope enrichments with sufficient precision, and at acceptable cost, in biological samples. In this article I will discuss the importance of micronutrient deficiencies globally, review some of the many stable isotope-based methodologies, and describe the analytical methods currently available. Highly enriched isotopes are becoming more available at acceptable cost. Currently, the greatest hurdle limiting wider use of stable isotope-based methods is the availability of sufficiently precise, accurate and cost-effective analysis of isotope ratios in biological samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), which is becoming more accessible, promises adequate precision at reasonable cost. It seems likely that HR-ICP-MS will be increasingly adopted as an analytical methodology, which will encourage collaborations between mass spectrometrists and clinicians/nutritionists. Such collaborations will benefit all participants, and increase understanding and knowledge about important micronutrient deficiencies worldwide.