Carbon, nitrogen, and sulfur elemental and isotopic variations in mouse hair and bone collagen during short-term graded calorie restriction

This study characterised the effect of calorie restriction (CR) on elemental content and stable isotope ratio measurements of bone “collagen” and hair keratin. Adult mice on graded CR (10-40%; 84 days) showed decreased hair δ15N, δ13C, and δ34S values (significantly for δ15N) with increasing CR, alongside a significant increase in bone “collagen” δ15N values and a decrease in “collagen” δ13C values. We propose this was likely due to the intensified mobilisation of endogenous proteins, as well as lipids in newly-synthesised “collagen”. Elemental analysis of bone “collagen” revealed decreased carbon, nitrogen, and sulfur % content with increasing CR which is attributed to a change in the in vivo bone “collagen” structure with extent of CR. This complexity challenges the use of elemental indicators in the assessment of collagen quality in archaeological studies where nutritional stress may be a factor.