Detection of breastfeeding and weaning in modern human infants with carbon and nitrogen stable isotope ratios

TLDR

The study longitudinally measured carbon and nitrogen stable isotope ratios in fingernail and hair samples from mother‑infant pairs with exclusive breastfeeding, mixed feeding, or exclusive formula feeding. Exclusively breastfed infants exhibited ~1‰ carbon and 2–3‰ nitrogen enrichment relative to mothers, whereas mixed or formula feeding reduced these enrichments; the faster decline of δ13C compared to δ15N during weaning shows that δ13C tracks solid food introduction and δ15N reflects breast‑milk duration, refining isotopic interpretations of breastfeeding and weaning. © 2005 Wiley‑Liss, Inc.; Am J Phys Anthropol, 2006.

Abstract

Abstract Carbon ( 13 C/ 12 C) and nitrogen ( 15 N/ 14 N) stable isotope ratios were longitudinally measured in fingernail and hair samples from mother‐infant pairs where infants were exclusively breastfed (n = 5), breast‐ and formula‐fed (n = 2), or exclusively formula‐fed (n = 1) from birth. All exclusively breastfed infants had a dual enrichment in carbon (≈1‰) and nitrogen (≈2–3‰) when compared to maternal values. In contrast, breast‐ and formula‐fed subjects had reduced enrichments compared to exclusively breastfed subjects, and the exclusively formula‐fed infant showed no increase in δ 13 C or δ 15 N values. This finding of a carbon trophic level effect in breastfeeding infants suggests that 13 C‐enrichments of approximately 1‰ in archaeological populations are not necessarily the result of the consumption of C 4 ‐based weaning foods such as maize or millet. During the weaning process, the δ 13 C results for breastfed infants declined to maternal levels more rapidly than the δ 15 N results. This suggests that δ 13 C values have the potential to track the introduction of solid foods into the diet, whereas δ 15 N values monitor the length of time of breast milk consumption. These findings can be used to refine the isotopic analysis of breastfeeding and weaning patterns in past and modern populations. Am J Phys Anthropol, 2006. © 2005 Wiley‐Liss, Inc.