Objective: To evaluate vitamin D binding protein and free 25-hydroxyvitamin D [25(OH)D] levels in healthy controls compared to primary hyperparathyroidism (PHPT) patients, and to examine PHPT before and after surgery. Methods: Seventy-five PHPT patients and 75 healthy age, gender, and body mass index (BMI) -matched control subjects were examined. In addition, 25 PHPT patients underwent parathyroidectomy and had a 3-month follow up visit. Levels of total and free 25(OH)D, DBP, and intact parathyroid hormone (iPTH) were determined before and 3 months after surgery. Results: There was no significant difference in age and BMI between PHPT patients and controls. Levels of 25(OH)D and DBP were lower in PHPT patients compared to controls ( p < 0.01). There was no significant difference in calculated free and bioavailable 25(OH)D levels between PHPT patients and controls. Calcium and iPTH levels decreased to normal but DBP and DBP-bound-25(OH)D increased ( P < 0.001) after parathyroidectomy. Levels of DBP were inversely correlated with iPTH ( r = −0.406, P < 0.001) and calcium levels ( r = −0.423, P < 0.001). Conclusion: Serum DBP levels were lower in patients with PHPT and parathyroidectomy restored DBP levels. We suggest that lower DBP levels is one of contributing mechanisms of low total 25(OH)D in PTHP patients and the total 25(OH)D levels might not reflect true vitamin D status in PHPT patients.
Osteomalacia is a bone disease more commonly seen and with greater clinical 'implications in North China than elsewhere (1, 2, 3). The principal cause of the skeletal demineralization resides in vitamin D deficiency, a combination of its lack in the diet and exclusion of sunlight. By reason of such deficiency, calcium given by mouth fails to be absorbed. Poor intestinal absorption rather than excessive elimination is incriminated because it has been demonstrated by the studies of Hannon et al. (4) that the endogenous calcium metabolism in patients with osteomalacia on low intake is within normal limits and that calcium administered parenterally is largely retained. Under such circumstances while the endogenous destructive activity in the bones may not be excessive, the reparative process is very much interfered with through defective intestinal absorption so that skeletal decalcification inevitably ensues. The limited intake of calcium in common Chinese dietaries (5), and periods of mineral stress incident to pregnancy and lactation are some of the contributing factors that enter into the pathogenesis of osteomalacia.Studies of the effect of vitamin D in the treatment of osteomalacia (4, 6) demonstrate the remarkable'conserving action of vitamin D on calcium and phosphorus metabolism. As a result of its administration, intestinal absorption is promoted and endogenous elimination is decreased so that large quantities of calcium and phosphorus are available for deposition in the bones. The actual amount of calcium and phosphorus retained depends upon the level and ratio of intake of these elements. It has been shown in two patients with osteomalacia undergoing reparation initiated by vitamin D (7) that calcium retention varied directly with calcium intake while phosphorus retention was limited by both calcium and phosphorus intake. Fecal calcium likewise varied directly with calcium intake while fecal phosphorus was parallel with both calcium and phosphorus intake. When calcium supply is limited in relation to phosphorus (low Ca: P ratio) practically all the calcium absorbed is deposited, none appearing in the urine. On the other hand, when phosphorus supply is short compared with calcium (high Ca: P ratio), all the available phosphorus is retained and urinary phosphorus vanishes. Conservation of excretion through the urinary tract and efficient absorption through the intestinal canal account for the markedly positive balances in osteomalacia when reparation is brought about under the influence of vitamin D.Similar observations on the effects of variations of the levels and ratios of calcium to phosphorus intake on their serum levels, paths of excretion and balances have been made on another patient with healing osteomalacia. But in contrast to the previous patients who received vitamin D only prior to the observations, the present subject was given vitamin D throughout the entire study so as to obviate any uncertainty in ascribing the metabolic results obtained to vitamin D action. Moreover, attempt was made in ...
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