Comparing apples and oranges: why infant bone collagen may not reflect dietary intake in the same way as dentine collagen

Objectives

Recent developments in incremental dentine analysis allowing increased temporal resolution for tissues formed during the first 1000 days of life have cast doubt on the veracity of weaning studies using bone collagen carbon (δ13C) and nitrogen (δ15N) isotope ratio data from infants. Here we compare published bone data from the well-preserved Anglo-Saxon site of Raunds Furnells, England, with co-forming dentine from the same individuals, and investigate the relationship of these with juvenile stature. The high resolution isotope data recorded in dentine allow us to investigate the relationship of diet with juvenile stature during this critical period of life.

Materials and methods

We compare incremental dentine collagen δ13C and δ15N data to published bone collagen data for 18 juveniles and 5 female adults from Anglo Saxon Raunds Furnells alongside new data for juvenile skeletal and dental age. An improvement in the method by sampling the first 0.5mm of the sub-cuspal or sub-incisal dentine allows the isotopic measurement of dentine formed in utero.

Results and Discussion

δ13C profiles for both dentine and bone are similar and more robust than δ15N for estimating the age at which weaning foods are introduced. Our results suggest δ15N values from dentine can be used to evaluate the maternal/in utero diet and physiology during pregnancy, and that infant dentine profiles may reflect diet PLUS an element of physiological stress. In particular, bone collagen fails to record the same range of δ15N as coforming dentine, especially where growth is stunted, suggesting that infant bone collagen is unreliable for weaning studies.