An integrative analysis of how zinc in teeth reflects maternal environments and predicts infant function in a rural Mexican community
The assessment and interpretation of zinc (Zn) concentrations derived from chemical analyses of biological hard tissues has been troubled by the complexities inherent in working with an essential trace element implicated in several important biological processes. Because Zn is subject to some homeostatic control by the body and does not undergo a clear trophic level separation several researchers have suggested its utility for paleodietary reconstruction is severely limited. However, with an understanding of the nature of Zn physiology, nutrient interactions and local factors affecting bioavailability it may yet be possible to utilize measures of hard tissue Zn concentrations in evaluating diet, health and children's functional outcomes.
Pre-and-postnatal enamel Zn levels were determined via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for 80 teeth collected from 46 infants participating in a large longitudinal study in the Solís Valley, Mexico, during the mid-1980s. Relationships between enamel Zn levels and ∼200 variables documenting maternal diet, infant growth, morbidity and cognitive development were explored.
The results indicate that an infant's prenatal enamel Zn content reflects their mother's pregnancy dietary quality. Infants born into the poorest households, and who were exposed to poor quality diets, have the highest concentrations of zinc in their prenatal enamel. Further, prenatal enamel Zn levels are predictive of the cognitive development of Solís infants. Postnatal enamel zinc amounts reflect maternal weight gain during pregnancy and predict the onset of certain illnesses (e.g. common cold, influenza) during infancy. The uptake of Zn by postnatal enamel is likely determined by mothers' storage of zinc in bone over the years preceding her pregnancy, as well as by both her pregnancy and lactation diets.
This research demonstrates that, despite the fact that zinc is an essential element, its variation within deciduous teeth can be understood in terms of variation in socioeconomic status and maternal diets, and that it can in turn be predictive of individuals' future functional outcomes. From a biocultural anthropological perspective these results are remarkable in that they clarify one of the mechanisms by which the biological effects of social inequality are recycled from one generation to the next.