The aetiology of senile osteoporosis: secondary hyperparathyroidism due to renal failure.

The aetiology of senile osteoporosis was investigated in a series of elderly normal persons (mean age 76.8 years) who were compared to 18-19 year old normal controls. Osteoporosis was estimated by standard radiological morphometric and densitometric techniques, in the metacarpals and thoraco-lumbar vertebrae. Serum parathyroid hormone levels were significantly higher in the elderly group, and correlated well with morphometric and densometric measurements of osteoporosis. Creatinine clearance was reduced in seven out of nine of the elderly group, and correlated well with the degree of osteoporosis. Serum thyrocalcitonin levels were reduced in the elderly. Tubular reaborption of phosphate and TmP/GFR were in the hyperparathyroid range in the elderly group and correlated well with the degree of osteoporosis. The hypothesis is advanced that the osteoporosis of old age is a result of parathyroid overactivity, caused by asymptomatic chronic renal failure. The suggestion is made that a diet low in phosphorus might reduce the incidence of osteoporosis in old age by reducing the parathyroid overactivity.