Epidemiological studies suggest that hypovitaminosis D is common in patients with primary hyperparathyroidism (PHPT). They have higher levels of serum parathyroid hormone (PTH) and markers of bone turnover, and more frequent fractures than vitamin D replete patients. There are concerns that vitamin D repletion in these patients might exacerbate pre-existent hypercalcaemia, although recent literature suggests this is uncommon.
We aimed to determine the effects of vitamin D replacement on biochemical indices of calcium metabolism in patients with combined PHPT and hypovitaminosis D in a predominantly Asian cohort.
Twenty-three patients with PHPT and hypovitaminosis D were studied: Asian:Caucasian 19:4; M:F 2:21; age (range) 59 (3185) years; basal calcium (mean±S.D.) 2.62±0.12 mmol/l, 25-OH vitamin D 14.8±7 nmol/l. Each received oral 20 000 IU cholecalciferol per week for 12 weeks.
Mean baseline serum calcium, phosphate, alkaline phosphatase and PTH were measured at week 4, 8 and 12 weeks. Mean 25-OH vitamin D levels before and after 12 weeks were compared and the relationship between 25-OH vitamin D and PTH was analysed.
A significant increase in 25-OH vitamin D was observed at 12 weeks: 14.8±7 vs 75.8±21 nmol/l, P=0.0001. A reduction in PTH was found at week 8; 21.9±11 vs 15.3±6, P=0.05, and at week 12; 21.9±11 vs 14.7±5, P=0.02. There was no significant change in calcium (P=0.85), phosphate (P=0.37) or alkaline phosphatase (P=0.94). PTH and 25-OH vitamin D levels were inversely correlated (r=−0.46; P=0.002).
Conclusion: We conclude that weekly vitamin D supplementation with 20 000 IU for a three month period corrects hypovitaminosis D in patients with mild PHPT without causing significant increases in calcium.