Experimental studies on osteoporosis.

Nutritional secondary hyperparathyroidism (NSH) defines a spontaneous and experimental disease in most domesticated and in some wild animals, caused by dietary calcium deficiency and/or phosphorus excess. Calcium deficiency results directly in hypocalcemia, and phosphorus excess induces hyperphosphatemia which causes hypocalcemia. Secondary hyperparathyroidism thus results and the plasma parameters return to normal and are maintained but only at the expense of progressive bone loss. The bone loss is generalized but the bones are not uniformly affected. The hierarchy of bone loss is, in decreasing order, the jaw bones, especially the alveolar bone, other skull bones, ribs, vertebrae and, finally, long bones. Osteocytic osteolysis is the main mechanism of resorption and application of this concept is a condition sine qua non in the interpretation of the histologic lesions. The early loss of alveolar bone constitutes the initial event in periodontal disease in animals. The osseous lesions in animal NSH are reversible by correction of dietary calcium and phosphorus levels, provided a hyperostotic osteodystrophia fibrosa has not yet developed. The applicability of animal NSH as a model for human osteopenic conditions, including periodontal disease and spinal osteoporosis, is supported by the very inadequate calcium and phosphorus nutrition in most Western countries. The diet is deficient in calcium and excessive in phosphorus; both conditions induce NSH in animals. The degree of dietary calcium deficiency, as influenced by geographic, economic, and social factors, is positively correlated to the degree of periodontal disease and osteoporosis in the population. Evidence is presented to show that the radiographic and histologic manifestations of human periodontal disease and osteoporosis are the same as those of animal NSH. Periodontal disease is therefore considered a fore-runner to the clinically more important spinal osteoporosis. Limited experiments in human periodontal disease indicate that added dietary calcium can positively influence the alveolar bone loss.