Endocrine Abstracts

We investigated calcium and bone metabolism in a group of 123 institutionalized volunteers between 60 and 98 years old, 73 females and 50 males. 25OH-D₃ was measured by an indoor RIA technique. 1.25(OH)₂D₃ was measured by HPLC, serum calcium by photocolorimetry, bone alkaline phosphatase by immunoenzymatic technique, whereas serum PTH and urinary deoxypyridinoline (DPD) were measured by IRMA. Almost all volunteers (92.6%) had low 25OH-D₃ values, but normal or even increased levels of the active hormone, 1.25(OH)₂D₃. High PTH was found in 40 cases (32.5%), of which three were primary hyperparathyroidism, whereas the others had low or low-normal calcium levels (secondary hyperparathyroidism). PTH-induced 1α hydroxylation in the elderly with undamaged kidney function seems to compensate the paucity of vitamin D substrate. More than half of the cases had high DPD levels, suggesting high bone turnover. Bone turnover parameters were higher in females than in males (P<0.05). A positive correlation between PTH and urinary DPD was noticed (R²=0.351), suggesting the role of secondary hyperparathyroidism in high turnover bone loss. We further supplemented the vitamin D intake in 42 volunteers with a daily dose of 2000 IU of 25-OHD₃ for three months in the summer period, whereas other 42 volunteers received placebo (vitamin B). Normalization of 25-OHD₃ levels was seen in both groups, suggesting that even mild sun exposure increases skin resources of vitamin D. A more significant increase in both 25OH-D₃ and 1.25(OH)₂D₃ was however observed in the vitamin D-treated group. Normalization of serum PTH, but not of turnover parameters was observed in both groups. Mild hypercalcemia and increase in serum creatinine were noticed in the vitamin D-treated group. Vitamin D supplementation might therefore be accompanied by hypercalcemic and nephrotoxic effects at doses higher than 2000 IU/day. Sunlight exposure seems efficient to replenish vitamin D reserves at institutionalized patients.