The Impact of Diet and Health on Bone Stable Isotope Ratios: A Comparative Study

There is a bidirectional interaction across nutrition, infection and immunity. While good nutrition increases the immune system's response, immune deficits following malnutrition early in life have been shown to persist for weeks and even years. This study combines osteological and archaeometric analysis providing significant novel perspectives on the synergy between diet and health exploring stable isotope analysis. It is intended to assess whether stable isotope analysis can be used as a tool to study the impact of diet on the individuals' susceptibility to pathogens. This study will help understanding the physiological mechanisms of stress and disease prior to the advent of modern medicine and antibiotics, as well as improve dietary isotope data interpretation.

The samples under study were recovered from Santa Maria do Olival, Tomar, Portugal (11th - 17th centuries). Stable isotope analyses were performed to 66 skeletons, 33 individuals without macroscopic indicators of physiological stress or skeletal lesions and 33 individuals with skeletal lesions of possible infectious origin (n=23) or healed fracture calluses (n=10). Stable isotope analyses were also preformed to fauna remains (n=13) to estimate the baseline diet. The individuals with lesions were divided into active (n=6) and healed lesions (n=7), a combination of active and healed lesions (n=10) and fracture calluses (n=10) and the data compared with sites within the same bone without lesions. In total 134 samples (94 from long bones, 27 from ribs, 13 from faunal remains) were used for stable isotope analyses. Carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S) stable isotopes were used to estimate the diet at Tomar. δ13C and δ15N values were compared between individuals with and without lesions and non-lesion and lesion sites were also compared within the same bone.

The diet at Tomar was complex (δ13C=-18.6±0.5‰, δ15N=10.8±0.8‰, δ34S=13.1±1.5‰), low in terrestrial animal protein and high in aquatic protein intake, despite its inland location. No statistically significant differences (p>0.05) were found between sexes or socio-economic status. δ15N differed significantly between skeletons with non-specific generalised infections (δ13C=-18.7±0.8‰, δ15N=9.9±0.4‰) and those with only healed tibial periosteal reactions (p