TOTAL PARENTERAL-NUTRITION AND ITS EFFECTS ON BONE METABOLISM

Total parenteral nutrition (TPN) may affect bone metabolism in a varie ty of ways. These may include potential indirect effects such as on ga strointestinal hormone secretion, liver function, especially cytochrom e P450 isoenzymes, metabolic biorhythms where established, and the con tinuous compared with the intermittent supply of nutrients. More subst antial evidence exists for the reduction of bone formation, parathyroi d hormone secretion, and calcitriol production in TPN patients along w ith high urinary calcium excretion. This review considers both aluminu m loading and vitamin D sensitivity as etiologic factors and suggests that aluminum may have played a primary role in the pathogenesis of th ese abnormalities in bone and mineral metabolism, but that vitamin D m ay have potentiated the deleterious actions of aluminum. While the sou rces of aluminum contamination of TPN solutions have been identified a nd efforts are under way to reduce its contamination of TPN solutions, the persistence of low bone mass measurement in TPN patients is a pro blem that has been identified repeatedly, does not have a current expl anation, and requires further study.