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Objective: Normocalcemic primary hyperparathyroidism (NPHPT) is characterized by elevated parathyroid hormone (PTH) levels with persistently normal calcium levels. The diagnosis of NPHPT assumes the absence of secondary causes of elevated PTH levels. The objective of the current study was to examine levels of free 25-hydroxyvitamin D (25[OH]D) in NPHPT subjects and healthy controls. Methods: Ten NPHPT subjects and 20 controls who were age, sex, race, and body mass index (BMI) matched were examined. The diagnosis of NPHPT was made if subjects had (1) a serum calcium level of 8.6 to 10.4 mg/dL, total 25(OH)D 30 to 40 ng/mL, and intact PTH (iPTH) ≥66 pg/mL; and (2) normal renal and liver function. Serum total 25(OH)D levels were measured by radioimmunoassay, and free 25(OH)D levels were determined using an enzyme-linked immunoassay. Results: Mean age of NPHPT subjects was 59.9 ± 5.4 years, and mean BMI was 28.4 ± 2.3 kg/m2, which was not significantly different from the mean age and BMI of the control subjects. Mean total 25(OH)D level was 31.9 ± 1.7 ng/mL in NPHPT subjects and did not differ from that of the controls (32.7 ± 3.3 ng/mL; P = .52). However, mean free 25(OH)D was 5.0 ± 0.9 pg/mL in NPHPT subjects, which was 20% lower compared to the mean of the controls (6.2 ± 1.3 pg/mL; P = .013). Serum iPTH levels were inversely correlated with levels of measured free 25(OH)D (r = -0.42; P .10). Conclusion: Measured free 25(OH)D levels are lower in NPHPT subjects than in healthy control subjects. We suggest that some NPHPT subjects may actually have secondary hyperparathyroidism based on their free 25(OH) D levels. Abbreviations: 25(OH)D = 25-hydroxyvitamin D; BMI = body mass index; CV = coefficient of variation; DBP = vitamin D-binding protein; iPTH = intact parathyroid hormone; NPHPT = normocalcemic primary hyperparathyroidism.

To examine the relationship between endogenous serum estradiol and vitamin D-binding protein (DBP) and total, free, and bioavailable 25-hydroxyvitamin D (25OHD) concentrations in pre- and postmenopausal women.In 165 healthy women (ages, 26 to 75 years) not taking any form of exogenous estrogen, the serum concentrations of estradiol, 25OHD, DBP, parathyroid hormone, and albumin were measured. Free and bioavailable 25OHD (free + albumin-bound) levels were calculated from total 25OHD, DBP, and serum albumin levels.Premenopausal women had higher serum 25OHD (31.5 ± 7.9 ng/mL), DBP (45.3 ± 6.2 mg/dL), and estradiol (52.8 ± 35.0 pg/mL) levels than postmenopausal women (26.5 ± 4.9 ng/mL, 41.7 ± 5.7 mg/dL, and 12.9 ± 4.9 pg/mL), respectively. In addition, the calculated free and bioavailable 25OHD levels were higher in pre- than postmenopausal women (P.05). Serum estradiol correlated with DBP (r = 0.22; P.01) and total 25OHD (r = 0.27; P.01). In multivariate regression models (with or without serum 25OHD), estradiol was independently associated with DBP (P.05).Lower estradiol level is one of the factors that contribute to lower DBP levels in older women. Our data indicate that besides well-known factors such as age, gender, and race, serum estradiol concentrations are also a physiologic predictor of DBP concentration.

Objective: To determine whether low levels of vitamin D-binding protein (DBP) are related to 25-hydroxyvitamin D (25[OH]D) deficiency in female patients with primary hyperparathyroidism (PHPT). Methods: Twenty-five female patients with PHPT (serum calcium level >10.2 mg/dL and intact parathyroid hormone (iPTH) level >66 pg/mL) and 25 healthy age- and body mass index-matched female control subjects were enrolled. Serum calcium and iPTH levels were determined by commercial laboratories. Levels of 25(OH)D and 1,25-dihydroxyvitamin D (1,25[OH] 2 D) were determined by radioimmunoassay, and DBP level was determined by enzyme-linked immunosorbent assay. Results: Serum iPTH and calcium levels were higher in PHPT patients than control subjects (P

Objective To review the current literature investigating the association of plasma parathyroid hormone (PTH) with the prevalence of metabolic syndrome and the risk for cardiovascular disease (CVD). Methods We conducted a search of PubMed and Medline database using the terms hyperparathyroidism, metabolic syndrome, hypertension, hyperlipidemia, hyper-glycemia, and CVD. We reviewed relevant studies from 2004 to 2012. Results The current literature assessing the association of plasma PTH levels with metabolic syndrome and CVD is inconsistent; however, positive associations among hyperparathyroidism, metabolic syndrome, and CVD were found in a majority of the studies. The differences in the study populations may partly explain the mixed results. Conclusion In the general population, a high serum PTH level predisposes patients to CVD mortality. Further research is needed to determine the role of PTH in the etiology of metabolic syndrome and CVD. (Endocr Pract. 2013;19:712-717)