| Abstract: |
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. pg 188 \bDiet\b High carbohydrate and high fiber diets can lead to loss of calcium and thus predispose to osteopenia {Birnbaum 1992
Yanagawa et al 1992}. Although the diet characterized isotopically by White and Schwarz {!White and Schwarz 1994} would have been high in carbohydatres, there is no difference between the carbohydrate content of wheat barely species (n=5, mean=71.98 # 2.85g/100g edible portion) and that of sorghum/illet species (n=15, mean = 71.98 # 2.57g/100g edible portion) {Wu Leung et al 1968}. ...then talks of fiber If fibre consumption is a main etiological factor in Nubian osteopenia, then pathological individuals might exhibit lighter delta<sup>13</sup>C values i.e. be consumers of more <sup>13</sup>C plants. pg 189 The amount of calcium available for bone formation might also depend on the ratio of calcium to phosphorus in the diet. High phosphorus, low calcium intake may cause a secondary hyperparathyroidism which leads to a corresponding imbalance in plasma levels, ulitmately resulting in bone resorption {Avioli 1993
Calvo 1993}. Reduced manesium absorption is also implicated in osteopenia {Schwartz 1990}. Other dietary factors not testable using the istopic method include caffeine, sodium, and alcohol consumption {Lore 1989
Birnbaum 1992
Stini 1995}. Clinical and cross-cultural studies suggest that high protein diets create a risk for osteopenia {Olson et al 1981
Licada et al 1981
Yuen et a l 1984
Yano et al 1985
Einhorn 1990
Abelow et al 1992
Hu et al 1993} because calcium reabsorption in the kidney is depressed and more calcium is excreted {Heaney et al 1982
Kerstetter and Lindsay 1990}.
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