Effect of Low Vitamin D on Volumetric Bone Mineral Density, Bone Microarchitecture and Stiffness in Primary Hyperparathyroidism.

Context: Patients with 25-hydroxyvitamin D deficiency (25OHD <20 ng/ml) and primary hyperparathyroidism (PHPT) have more severe disease reflected by higher serum PTH levels compared to those with vitamin D levels in the insufficient (20-29 ng/ml) or replete range (>= 30 ng/ml). Objective: To study the effect of low vitamin D in PHPT on volumetric bone mineral density (vBMD), bone microarchitecture, and bone strength. Design, Setting, and Participants: This is a cross-sectional analysis of 99 PHPT patients with and without 25OHD insufficiency and deficiency from a university hospital. Outcome Measures: Bone microarchitecture and strength were assessed with high-resolution peripheral quantitative computed tomography (HRpQCT), microfinite element analysis, and individual trabecula segmentation. Results: In this cohort, 25OHD levels were deficient in 18.1%, insufficient in 35.4% and replete in 46.5%. Those with lower 25OHD levels had higher PTH (P < .0001), were younger (P = .001) and tended to weigh more (P = .053). There were no age-, weight- and sex-adjusted between-group differences (< 20 vs 20-29 vs >= 30 ng/ml) in any HRpQCT, microfinite element analysis, or individual trabecula segmentation indices. Because few participants had 25OHD below 20 ng/ml, we also compared those with 25OHD below 30 vs at least 30 ng/ml and found only a trend toward lower adjusted cortical vBMD(3.1%, P = .08) and higher cortical porosity (least squares mean +/- SEM7.5 +/- 0.3 vs 6.6 +/- 0.3%, P = .07) at the tibia but not the radius. Stiffness did not differ at either site. In multiple regression analysis, 25OHD accounted for only three of the 49.2% known variance in cortical vBMD; 25OHD was not significant in the model for cortical porosity at the tibia. Conclusion: Low 25OHD levels are associated with higher PTH levels in PHPT, but contrary to our hypothesis, these differences did not significantly affect vBMD or microarchitecture, nor did they result in lower stiffness. Low vitamin D in PHPT using current 25OHD thresholds for insufficiency and deficiency did not significantly affect skeletal integrity as assessed by HRpQCT.