Vitamin D deficiency influences histomorphometric features of bone in primary hyperparathyroidism

Vitamin D deficiency is common in patients with primary hyperparathyroidism (PHPT). The presence of low levels of vitamin D may affect the skeletal consequences of PHPT.

In this cross-sectional study, transiliac crest bone biopsies were performed after double tetracycline labeling in patients with mild PHPT and analyzed according to serum levels of 25 hydroxyvitamin D (25OHD).

We studied 30 patients with mild PHPT (age 53 ± 11 years; 67% women; calcium 11.1 ± 1.0 mg/dl; PTH 149 ± 129 pg/ml). Serum 25OHD levels were low in the majority of subjects (mean 21 ± 11 ng/ml) and inversely associated with PTH (r = -0.69; p < 0.01). 25OHD levels were directly associated with cortical width (Ct.Wi; r = 0.46, p < 0.03) and trabecular separation (Tb.Sp; r = 0.41; p < 0.04), but inversely associated with cancellous bone volume (BV/TV; r = -0.39, p < 0.04). Subjects with 25OHD levels < 20 ng/ml (n = 14) and ≥ 20 ng/ml (n = 16) were compared. Groups did not differ by age, sex, menopausal status, serum calcium, creatinine, or 1,25(OH)₂D. PTH was 1.8-fold higher in subjects with 25OHD < 20 (265 ± 166 pg/ml vs. 95 ± 50 pg/ml; p < 0.01). On histomorphometric analysis, those with low 25OHD had lower Ct.Wi (541 ± 167 microm vs. 712 ± 200 microm; p < 0.03). Conversely, measures of trabecular microarchitecture were better in those with lower 25OHD, with higher BV/TV (26.1 ± 6.1% vs. 20.4 ± 6.4%; p < 0.03), greater trabecular number (Tb.N: 2.0 ± 0.4 mm⁻¹ vs. 1.8 ± 0.4 mm⁻¹; p < 0.04) and lower Tb.Sp (371 ± 90 microm vs. 472 ± 137 microm; p < 0.04). There were no differences between the groups in bone remodeling indices.

Low levels of 25OHD in patients with PHPT are associated with higher concentrations of PTH, greater catabolic effects in cortical bone and greater anabolic effects in trabecular bone.