Clinical significance of vitamin D deficiency in primary hyperparathyroidism, and safety of vitamin D therapy.

Vitamin D deficiency occurs more frequently in patients with primary hyperparathyroidism (PHPT) compared with the general population, and is usually associated with an aggravated form of the disease. Current guidelines recommend measurement of serum levels of 25-hydroxy vitamin D (25-OHD) in all patients with PHPT, and their repletion if the levels are less than 50 mmol/L (20 ng/mL). Limited data suggest that vitamin D treatment is generally safe in subjects with mild PHPT and coexisting vitamin D deficiency. Adverse effects include hypercalcuria and, less commonly, exacerbation of hypercalcemia. Well-designed trials are needed to evaluate the safety of vitamin D replacement therapy in a wide spectrum of patients with concomitant PHPT and vitamin D deficiency. These trials should address the impact of such therapy on the complications and course of PHPT.