Stable carbon and nitrogen isotope values of bone and teeth reflect weaning age at the medieval Wharram Percy Site, Yorkshire, U.K

Abstract

We report on the measurements of carbon and nitrogen stable isotopes of both bone and teeth from a single site and population (Medieval Wharram Percy), undertaken to explore variations due to weaning in a past population. There have been a number of recent studies of weaning using 15N values of ribs, and we indicate a number of assumptions that must be met before the results of such studies can be correctly interpreted. We found that rib collagen 15N values decrease to adult levels after age 2 years, indicating that weaning occurred at or before this age. Rib collagen 13C values are also more enriched than adult 13C values before age 2 years, and we argue that this is due to the so-called carnivore effect in 13C. We measured teeth and rib 15N values from the same individuals and found that for individuals up to age 11 years, tooth dentine 15N is higher than adult rib 15N values, indicating that the dentine was formed during breast-feeding and that there was almost no turnover of dentine since. We observed some decrease in 13C and 15N rib values, compared to adult rib and teeth values, for the few years after weaning that may relate to a theoretically predicted physiological nitrogen imbalance during this period of rapid growth, but this is more likely due to a childhood diet (up to age 9) which was isotopically different from later diet, possibly consisting of a greater proportion of plant foods