Osteopenia and stable isotope ratios in bone collagen of Nubian female mummies.

Stable carbon and nitrogen isotopes were analysed on bone collagen of 43 Sudanese Nubians from the X-Group period to test dietary hypotheses for the high frequency of osteopenia in this population. Stable carbon isotope ratios indicate that both normal and osteopenic individuals consumed the same mixed diet of C3 and C4 sources, which are assumed to have been constituted by the grain staples wheat/barley and sorghum/millet respectively. Females with osteopenia, however, have significantly elevated delta 15N values. The enrichment effect is greatest in the third and fifth decades of life, and is consistently patterned with microstructural and frequency differences previously reported by other researchers. It is suggested that delta 15N is reflecting differences in urea excretion and the renal processing and clearance of calcium and phosphorus. The study not only alerts us to the susceptibility of stable nitrogen isotopes to non-dietary (i.e. physiological) factors, but also identifies nitrogen isotope ratios as a possible new marker for osteopenia.