The effects of calcium supplementation to patients with primary hyperparathyroidism and a low calcium intake

Summary.

Background: In patients with primary hyperparathyroidism (PHPT) a low calcium intake might cause increased bone loss and thus aggravate osteoporosis, and a high intake might increase serum calcium level and the risk of nephrolithiasis. Aim of the study: Generally, guidelines recommend a normal calcium intake, and accordingly, those with a low intake might benefit from a modest calcium supplementation. This hypothesis was tested in the present study. Methods: Thirty-one patients with asymptomatic PHPT were recruited from an epidemiological study (The Tromsø study 1994/95). Those with a daily calcium intake below 450 mg were given calcium supplementation (500 mg Ca²⁺), and those with an intake above 450 mg were followed without supplementation. The study was open and lasted 1 year. Serum levels of calcium, PTH, 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D, urinary calcium excretion, blood pressure, and bone mineral density (BMD) were measured. Results: Three subjects dropped out without reason, 1 developed abdominal discomfort from the calcium supplementation, and 3 had an increase in serum calcium of more than 0.2 mmol/L and were therefore excluded. The latter three did not differ from the rest of the group at baseline. Of the remaining 24 that completed the study, 17 were given calcium. In this group there was a non-significant increase in serum calcium and urinary calcium excretion, a significant decrease in PTH after 4 weeks (13.2 (6.0) vs 9.4 (3.0) pmol/L, P < 0.05), and a significant increase in BMD at the femoral neck at the end of the study (0.849 (0.139) vs 0.870 (0.153) g/cm², P < 0.05). The blood pressure was not significantly affected. Conclusions: Most patients with mild PHPT and a low calcium intake tolerate a moderate calcium supplement. This may have beneficial effects on the bones, but the patients must be followed carefully.