Calcium homeostasis in the elderly
The initial aims of this investigation were to develop a reliable assay system for measuring serum 1,Z5-dihydroxyvitamin D [1,Z5(OH)ZD] concentrations and to establish a normal range in young healthy adults. Compared with young healthy individuals, the elderly population are indeed vitamin D deficient. Vitamin D deficiency was also demonstrated in a group of elderly osteomalacic patients. Slight improvements in osteomalacia was achieved by one month of treatment with vitamin D3' or alphacalcidiol with or without calcium supplements. The improvements were small and occured slowly. A significant increase in the strength of bone seems unlikely to occur in the short term. On the present evidence the combination of alphacalcidiol and calcium supplements seems no better than vitamin D3 or alphacalcidiol alone although it may require closer monitoring to avoid hypercalcaemia. In a group of elderly patients with osteoporosis and femoral neck fracture (FNF), serum osteocalcin concentrations rose significantly in the first week after fracture fixation. The change in osteocalcin correlated well (p < 0.001) with the change in serum 1,Z5(OH)ZD concentration. Histomorphometric measurements of the extent of osteoid correlated better with osteocalcin than alkaline phosphatase. Serum concentrations of 1,Z5(OH)ZD were also reduced in elderly patients with FNF irrespective of the presence of osteomalacia and therefore cannot be used as a screening test for osteomalacia in this patient group. Reduction of 1,Z5(OH)ZD was not due to a reduction in vitamin D binding protein. It is suggested that the low rate of bone turnover in these elderly patients reduces the requirement of vitamin D. Of the ten elderly patients who had underwent laryngo pharyngeal surgery all developed hypocalcaemia. This immediate post-operative decrease, due to a rapid reduction in circulating PTH concentrations, lead to an overall increase in urinary calcium excretion. Serum concentration of 1,25(OH)2D also fell postoperatively thus potentiating the hypocalcaemic state in these patients. Thus, it is important to give parenteral feeding supplemented with calcium and vitamin D, preferably alphacalcidiol. If delayed then profound as well as prolonged hypocalcaemia can occur. The human osteosarcoma cell 20S metabolised 25(OH)D3 in a substrate concentration and time dependent manner to produce products which were secreted into the extracellular medium. These products eluted from HPLC with a retention time coincident with 24,25(OH)2D3 and exhibited an UV absorption spectrum characteristic of a vitamin D sterol. Mass spectroscopy analysis indicated at least two products were synthesised by the cells. One was identical to 24,25(OH)2D3; the other appeared to be an unsaturated trihydroxylated derivative of vitamin D3.