Dynamic homeostasis modeling of Zn isotope ratios in the human body

Recent research performed on volunteers and patients suggested that diet, health, and basal metabolic rates (BMR) are factors controlling the bodily Zn isotope compositions (isotopic homeostasis). However, our poor understanding of the variability of Zn distribution among the different organs and fluids of the human body, and the ensuing isotope fractionation, limits the use of this isotopic system as a typical diagnostic tool for cancers and for past hominin diet reconstructions. Using box model calculations, we investigated the dynamics of Zn isotope variability in blood and other body tissues as well as the consistency of the hypothesis of heavy Zn isotope accumulation through time in the human body. We compare the results of the model with data obtained from control feeding experiments and from archeological samples. Model simulations indicate that the absence of an aging drift in non-circumpolar populations cannot be explained by their lower BMR. We argue that the drift observed in the blood of a circumpolar population results from a differential diet between young and older individuals in this population. When applied to the delta Zn-66 measured in blood, bones, or teeth, the present box model also offers insight into the isotope composition of the human diet, and therefore into its nature. Applying the model to isotopic observations on the remains of past hominins is a promising tool for diet reconstruction.