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 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. MATERIALS AND METHODS: 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. RESULTS AND DISCUSSION: 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.

Weaning at Anglo-Saxon Raunds: Implications for changing breastfeeding practice in Britain over two millennia.

This study investigated stable-isotope ratio evidence of weaning for the late Anglo-Saxon population of Raunds Furnells, Northamptonshire, UK. δ(15)N and δ(13)C values in rib collagen were obtained for individuals of different ages to assess the weaning age of infants within the population. A peak in δ(15) N values at about 2-year-old, followed by a decline in δ(15) N values until age three, indicates a change in diet at that age. This change in nitrogen isotope ratios corresponds with the mortality profile from the site, as well as with archaeological and documentary evidence on attitudes towards juveniles in the Anglo-Saxon period. The pattern of δ(13) C values was less clear. Comparison of the predicted age of weaning to published data from sites dating from the Iron Age to the 19th century in Britain reveals a pattern of changing weaning practices over time, with increasingly earlier commencement and shorter periods of complementary feeding in more recent periods. Such a change has implications for the interpretation of socioeconomic changes during this period of British history, since earlier weaning is associated with decreased birth spacing, and could thus have contributed to population growth.