Plasma 25-hydroxyvitamin D and not 1,25-dihydroxyvitamin D is associated with parathyroid adenoma secretion in primary hyperparathyroidism: a cross-sectional study.

BACKGROUND: Primary hyperparathyroidism (PHPT) is associated with reduced plasma 25-hydroxyvitamin D (P-25OHD) and usually increased plasma 1alpha,25-dihydroxyvitamin D (P-1,25(OH)2D). Parathyroid tissue expresses the vitamin D receptor and it is thought that circulating 1,25(OH)2D participate in the regulation of parathyroid cell proliferation, differentiation and secretion. AIM: To investigate the relations between circulating levels of 1,25(OH)2D and 25OHD respectively and parathyroid adenoma weight (AW), plasma-parathyroid hormone (P-PTH) and PTH secretion expressed as P-PTH/AW.
DESIGN: Cross-sectional study. MATERIAL: One hundred and seventy-one consecutive hypercalcaemic caucasian patients aged 19-87 years (median 63, 84% females) with surgically proven parathyroid adenoma.
RESULTS: A weak positive correlation was found between P-25OHD and P-1,25(OH)2D (r=0.24, P<0.005). AW depended on sex and body mass index. Following adjustment, it was correlated positively to P-PTH, calcium (Ca) and alkaline phosphatase (AP) and inversely to plasma phosphate in a multiple regression model. AW was not associated with vitamin D metabolites. Preoperative P-PTH correlated positively to plasma levels of Ca and AP, but inversely to phosphate and 25OHD (P<0.001) levels. P-PTH was not associated with P-1,25(OH)2D (P=0.65). The P-PTH:AW ratio correlated inversely to P-25OHD (P<0.05), but showed no relations to plasma levels of Ca, phosphate or 1,25(OH)2D (P=0.22).
CONCLUSION: In this material, low levels of 25OHD were related to higher levels of P-PTH and higher PTH:AW ratios in patients with PHPT suggesting that vitamin D deficiency increase PTH secretion activity. Neither PTH secretion nor AW was associated with circulating levels of 1,25(OH)2D.