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

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.

Carbon (δ¹³ C) and nitrogen (δ¹⁵ N) 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.

Long bones with active lesions had a significantly higher average δ¹⁵ N (δ¹⁵ N = 11.1 ± 0.9‰) compared to those without lesions (δ¹⁵ N = 10.7 ± 0.7‰; p = .02), while fracture calluses showed the largest range for both δ¹⁵ N and δ¹³ C. There were no significant differences in stable isotope ratios when compared between nonlesion and lesion sites in the ribs.

The increase in δ¹⁵ N seen in active lesions, when compared with δ¹⁵ N from nonlesion regions on the same long bone, may be a consequence of altered protein metabolism. The high variability of δ¹⁵ N and δ¹³ C 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.