Calcium isotope ratios in animal and human bone

Calcium isotopes in tissues are thought to be influenced by an individual's diet, reflecting parameters such as trophic level and dairy consumption, but this has not been carefully assessed. We report the calcium isotope ratios (delta Ca-44/42) of modern and archaeological animal and human bone (n = 216). Modern sheep raised at the same location show 0.14 +/- 0.08 parts per thousand higher delta Ca-44/42 in females than in males, which we attribute to lactation by the ewes. In the archaeological bone samples the calcium isotope ratios of the herbivorous fauna vary by location. At a single site, the archaeological fauna do not show a trophic level effect. Humans have lower delta Ca-44/42 than the mean site fauna by 0.22 +/- 0.22 parts per thousand, and the humans have a greater delta Ca-44/42 range than the animals. No effect of sex or age on the calcium isotope ratios was found, and intra-individual skeletal delta Ca-44/42 variability is negligible. We rule out dairy consumption as the main cause of the lower human delta Ca-44/42, based on results from sites pre-dating animal domestication and dairy availability, and suggest instead that individual physiology and calcium intake may be important in determining bone calcium isotope ratios. (C) 2010 Elsevier Ltd. All rights reserved.