The effect of growth on stable nitrogen isotope ratios in subadult bone collagen



Stable nitrogen isotopes have been used to reconstruct infant feeding practices as nursing infants have elevated δ15N ratios compared with their mothers. However, infancy is also a time of rapid growth, which may alter nitrogen isotope diet-to-tissue spacing. Several studies have documented a decrease in δ15N during growth in tissues with relatively fast accretion rates. This study investigates the effect that the growth of long bones, via collagen accretion, has on δ15N ratios. Long bones from individuals aged seven to nineteen years were obtained from a protohistoric ossuary in Ontario, Canada. Analysis of juveniles and adolescents permitted the examination of growth in a group who were not also nursing. It is concluded that a nitrogen isotope growth effect is not detectable in bone collagen from juveniles and adolescents, because: (1) δ15N ratios are not significantly different among the epiphyses, metaphyses and diaphysis of a growing long bone; (2) δ15N ratios are not significantly different between faster-growing versus slower-growing metaphyses; and (3) δ15N ratios are not significantly different between bones (or areas of a bone) that are still undergoing growth, versus bones that have ceased growing. The relatively slow speed of collagen accretion may explain why a growth effect is not manifested. Ultimately this research lends support to the use of nitrogen isotopes from bone collagen for infant feeding reconstructions. Copyright © 2009 John Wiley & Sons, Ltd.