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

Recent developments in incremental dentine analysis allowing increased temporal resolution for tissues formed during the first 1,000 days of life have cast doubt on the veracity of weaning studies using bone collagen carbon (δ¹³ C) and nitrogen (δ¹⁵ N) 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.

We compare incremental dentine collagen δ¹³ C and δ¹⁵ N 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 0.5 mm of the sub-cuspal or sub-incisal dentine allows the isotopic measurement of dentine formed in utero.

δ¹³ C profiles for both dentine and bone are similar and more robust than δ¹⁵ N for estimating the age at which weaning foods are introduced. Our results suggest δ¹⁵ N 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 δ¹⁵ N as co-forming dentine, especially where growth is stunted, suggesting that infant bone collagen is unreliable for weaning studies.