Effect of different healing stages on stable isotope ratios in skeletal lesions

Introduction Physiological stress is one of the various factors that can have an impact on stable isotope ratios. However, its effect on bone collagen stable isotope ratios is still not fully understood. This study aims to build on previous research on how different disease stages may affect bone collagen stable isotope ratios. Materials and Methods Carbon (δ13C) and nitrogen (δ15N) isotope ratios were assessed in 33 skeletons that retained evidence of infectious disease and healed fractures. Samples were taken from active lesions (long bones n = 14; ribs n = 4), healed lesions (long bones n = 10; ribs n = 9), or a fracture callus (long bones n = 9; ribs n = 3). Results were compared to stable isotope ratios calculated for regions on these bones that did not retain evidence of disease or fracture. Results Long bones with active lesions had a significantly higher average δ15N (δ15N = 11.1 ± 0.9‰) compared to those without lesions (δ15N = 10.7 ± 0.7‰; p = .02), while fracture calluses showed the largest range for both δ15N and δ13C. There were no significant differences in stable isotope ratios when compared between nonlesion and lesion sites in the ribs. Discussion The increase in δ15N seen in active lesions, when compared with δ15N from nonlesion regions on the same long bone, may be a consequence of altered protein metabolism. The high variability of δ15N and δ13C in fractures may be related to different healing stages of the calluses. This study suggests that stable isotope data can contribute information about diseases in the past, as well as an individual's response to diseases in the absence of modern medicine and antibiotics.