Is There Any Threshold for Vitamin D That Elevates Parathyroid Hormone

Abstract

Objective: To evaluate vitamin D status in relation to serum levels for parathyroid hormone (PTH) and corrected calcium among endocrine outpatients. Methods: A total of 760 patients (mean(SD) age: 40.0(12.6) years, 94.6% were females) admitted to our endocrinology outpatient clinic were included and evaluated with respect to patient demographics, serum levels for 25-hydroxyvitamin D (25(OH) D, ng/mL), PTH (pg/mL) and corrected calcium (mg/dL) as well as the vitamin D status. Results: Vitamin D deficiency was determined in 65.0% and elevated PTH levels in 20.3% of patients. iPTH levels were significantly higher in females than in males (58.9(40.4) vs. 45.1(26.2) pg/mL, p = 0.031) and in summer than in winter cases (63.9(47.7) vs. 54.2(32.8) pg/mL, p = 0.002), whereas no difference was found in serum levels for 25(OH) D, corrected calcium and phosphate with respect to gender and season. Significantly higher levels for iPTH were noted in vitamin D deficient patients (60.7(43.9) pg/mL) than in normal (51.1(33.4) pg/mL) and vitamin D insufficient (57.1(26.0) pg/mL) cases (p = 0.03). iPTH levels were correlated positively with age (r = 0.116, p = 0.001) and negatively with corrected calcium (r = −0.097, p = 0.008), P (r = −0.224, p = 0.000) and 25(OH) D (r = −0.134, p = 0.000), whereas no correlation was noted between 25(OH) D and corrected calcium levels. Conclusion: Our findings indicated that vitamin D deficiency in 65.0%, whereas PTH elevation only in 20.3% of endocrine outpatients, despite the significantly negative correlation of PTH to 25(OH) D and significantly higher levels of PTH among vitamin D deficient cases than in vitamin D insufficient and sufficient cases. Gender’s and seasonal differences had influence on serum levels for PTH but not on either 25(OH) D or corrected calcium, and no correlation was evident between 25(OH) D and corrected calcium levels.