Variations in oxygen isotopic compositions of human teeth and urinary stones

A previously reported, experimentally determined, relationship between the oxygen isotopic composition of bone and teeth phosphate (δ_p) and drinking water (δ_w), which has application to paleoclimatic interpretations, is shown to require modifications when applied to present day human populations. The oxygen isotopic compositions of 40 well documented human teeth and 11 urinary stones have shown that in both cases δ_p is well correlated wit δ_w. The slope of the linear regression ffit of this relationship is, however, lower than expected. This is explained by a mixing of intake waters from high and low latitudes in a diet of a modern human. Urinary stones are enriched in ¹⁸O by about 2% which we explain by: (a) different physiological (metabolic) rates of humans when teeth are formed (below the age of 20) compared to those rates when urinary stones form (generally in middle age); or (b) variations in the relative proportions of the different water intakes and outputs between healthy individuals and those forming urinary stones.