Hypovitaminosis D and Bone Mineral Metabolism and Bone Density in Hyperthyroidism

Abstract 

Little is known about the impact of concomitant vitamin D deficiency on bone mineral density in hyperthyroidism. Therefore, we evaluated bone mineral measures in vitamin D–deficient and sufficient patients with hyperthyroidism. Thirty newly diagnosed consecutive patients with hyperthyroidism were included. Blood samples were used for measurement of calcium, phosphate, alkaline phosphatase, 25-hydroxy vitamin D [25(OH) D], and parathyroid hormone (PTH). Bone mineral density (BMD) was measured at the hip, spine, and forearm. The patients were divided into vitamin D–deficient (<25nmol/L) and vitamin D–sufficient groups (≥25nmol/L). Eight (26.6%) patients had 25(OH) D levels less than 25nmol/L, with mean±standard deviation (SD) level of 16.5±3.2 (vitamin D–deficient group 1), and the remainder had a mean±SD of 46.0±13.5nmol/L (vitamin D–sufficient group 2). Serum-intact PTH levels were significantly higher in group 1 compared with those in group 2 (31.2±16.3 vs 18.0±13.1pg/mL; p=0.041). In the vitamin D–deficient group, the mean BMD T-scores were in the osteoporotic range at hip and forearm (−2.65±1.13 and −3.04±1.3) and in the osteopenia range at lumbar spine (−1.83±1.71). However, in vitamin D–sufficient group, the mean BMD T-scores were in the osteopenia range (−1.64±1.0, −1.27±1.6, and −1.60±0.7) at hip, forearm, and lumbar spine, respectively. The mean BMD Z-scores were also significantly lower in vitamin D–deficient group compared with those in vitamin D–sufficient group. Finally, BMD values (gm/cm²) at the hip and forearm were significantly lower in the vitamin D–deficient group compared with those in the vitamin D–sufficient group. In conclusion, hyperthyroid patients with concomitant vitamin D deficiency had lower BMD compared with vitamin D–sufficient patients.

Key Words: Bone mineral density, hyperthyroidism, hypovitaminosis D, thyrotoxicosis, vitamin D deficiency