Associate Professor Thomas WALCZYK

Dipl. Chem. 1990, University of Regensburg, Germany; Ph.D. 1994, University of Regensburg, Germany; Postdoc, 1994-1997 and Lecturer 1997-2007, ETH Zurich, Switzerland

Contact Information
Department of Chemistry, NUS 
3 Science Drive 3 
Singapore 117543 
Office: S13-05-11
Tel: (65) 6516 7986
Fax: (65) 6779 1691 

For more information, visit the group homepage: NutriTrace@NUS

Research Interests

Human Mineral and Trace Element Metabolism

Mineral and trace element deficiencies remain a major challenge to public health on a global scale. Iron deficiency and anemia, as the most prominent example, still affect one third of the world's population with its adverse effects on work performance, immune function and morbidity and mortality of mother and child around birth. Links between diet and health need to be better understood and translated into effective strategies for improving nutritional status, not only to save healthy life years but also to reduce growing burdens on health care systems.

Fig. 1: Elements in the diet that are needed for normal body function

Focus of my research is the development and application of stable isotope techniques for a better understanding of human element metabolism in health and disease. Radioisotopes have been used as tracers since decades in human studies but radiation hazards increasingly limit their use for research applications. Stable isotopes offer new perspectives as they do not decay and can be used without ethical concerns in humans. However, there full potential has not been exploited yet which I am trying to pioneer in my research:

1) Element absorption and bioavailability: by isotopic labeling of an element in the diet or a chemical compound, its bioavailability can be determined. Such information is needed for

  • design and evaluation of food fortification programs or dietary supplements
  • evaluation of physiological factors influencing element bioavailability
  • identification of nutrient/nutrient and nutrient/non-nutrient interactions for improving nutritional status through dietary advice.

Fig. 2: Factors influencing element bioavailability, i. e. the amount of an element in the diet that can be absorbed and utilized for physiological function

2) Isotopic labeling of the body: Stable isotopes do not decay and can be basically traced over years in the human body. After equilibration with the native element in the body, the fate of the tracer can be used to determine element turnover and element losses for

  • evaluation of potential strategies for improving mineral and trace element status
  • measurement of actual element requirements in the individual for maintaining nutritional status.

3) Isotope effects in the human body: Isotopic abundances of an element are not constant. They can be altered through element transport provided that element transport is mass-sensitive and non-quantitative. Deciphering the isotopic signatures that each individual bears in his or her body tissues may provide new insights into the mechanisms of element homeostasis and conditions of impairment.

Integral part of my research is the development of mass spectrometric techniques for high precision isotope analysis of biological samples. Facilities at NUS include a fully equipped thermal ionization mass spectrometry laboratory and dedicated facilities for inorganic trace element analysis. Complex questions are addressed through a broad multinational, interdisciplinary network including partners from medicine, pharmacology, analytical chemistry, physics, mathematics and statistics.

Representative Publications

  • Walczyk T., Muttayya S., Wegmueller R., Thankachan P., Sierksma A., Frenken L. G. J., Thomas T., Kurpad A. and Hurrell R. F. (2014) Inhibition of iron absorption by calcium is modest in an iron-fortified, casein- and whey-based drink in Indian children and is easily compensated for by addition of ascorbic acid. Journal of Nutrition, 144, 1703-1709.
  • Ren Y. and Walczyk T. (2014) Quantification of ferritin-bound iron in human serum using species-specific isotope dilution mass spectrometry. Metallomics, 6, 1709-1717.
  • Walczyk T., Kastenmayer P., Bonsmann S. S. G., Zeder C., Grathwohl D. and Hurrell R. F. (2013) Ferrous ammonium phosphate (FeNH4PO4) as a new food fortificant: iron bioavailability compared to ferrous sulfate and ferric pyrophosphate from an instant milk drink. European Journal of Nutrition, 52, 1361-1368.
  • Chen J. H., Shahnavas S., Singh N., Ong W. Y. and Walczyk T. (2013) Stable iron isotope tracing reveals significant brain iron uptake in adult rats. Metallomics, 5, 167-173.
  • Hotz K. and Walczyk T. (2013). Natural iron isotopic composition of blood is an indicator of dietary iron absorption efficiency in humans. Journal of Biological Inorganic Chemistry, 18, 1-7.
  • Chew G. and Walczyk T. (2013) Measurement of isotope abundance variations in nature by Gravimetric Spiking Isotope Dilution Analysis (GS-IDA). Analytical Chemistry, 85, 3667-3673.
  • Walczyk T. (2012) The Use of Stable Isotope Techniques for Studying Mineral and Trace Element Metabolism in Humans. In Vanhaecke F. and Degryse P. (Eds.), Isotopic Analysis: Fundamentals and Applications Using ICP-MS (435-494). Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA.
  • Hotz K., Augsburger H. and Walczyk T. (2011) Isotopic signatures of iron in body tissues as a potential biomarker for iron metabolism. Journal of Analytical Atomic Spectrometry, 26, 1347-1353.
  • Hoppler M., Zeder C. and Walczyk T. (2009) Quantification of ferritin-bound iron in plant samples by isotope tagging and species-specific isotope dilution mass spectrometry. Analytical Chemistry, 81, 7368-7372.
  • Denk E., Hillegonds D., Hurrell R. F., Vogel J., Fattinger K., Huselmann H. J., Kraenzlin M. and Walczyk T. (2007) Evaluation of Calcium-41 as a new approach to assess changes in bone metabolism: effect of a bisphosphonate intervention in postmenopausal women with low bone mass. Journal of Bone and Mineral Research, 22, 1518-1525.
  • Walczyk T. (2005) Iron speciation in biomedicine. In Handbook of Elemental Speciation II: Species in the Environment, Food, Medicine & Occupational Health. Cornelis R., Crews H., Caruso J. and Heumann K. G. (Eds.) 218-238. John Wiley & Sons, Ltd.
  • Walczyk T. and von Blanckenburg F. (2002) Natural iron isotope variations in human blood. Science, 29, 2065-2066.