Secondary hyperparathyroidism and lower hip bone mineral density in very old hospitalized adults: a real-world endocrine bone study.

BACKGROUND: Population ageing is associated with increasing rates of osteoporosis, frailty, and functional decline. Vitamin D deficiency and disturbances in calcium-parathyroid hormone (PTH) homeostasis are common in older adults and may contribute to bone loss. However, real-world data describing the frequency and skeletal relevance of these endocrine abnormalities in very old hospitalized populations remain limited. MATERIALS AND METHODS: We conducted a retrospective cross-sectional study including 1,202 hospitalized patients aged ≥70 years (mean age 85.0 ± 7.1 years) who underwent dual-energy X-ray absorptiometry at a tertiary endocrine and geriatric centre in Germany. Serum 25-hydroxyvitamin D, calcium, parathyroid hormone (PTH), thyroid-stimulating hormone (TSH), and renal function parameters were extracted from electronic medical records. Hip bone mineral density (BMD) served as the primary skeletal outcome. Multivariable linear regression models were used to assess associations between endocrine parameters and BMD after adjustment for age, sex, body mass index, and living setting. RESULTS: Vitamin D deficiency was highly prevalent in this very old cohort. Vitamin D levels <20 ng/mL were present in 68.6% of participants with available vitamin D measurements, and levels <10 ng/mL in 45.5%. Hypocalcaemia was observed in 39.1% of participants, while elevated PTH levels occurred in 29.9%. The combination of hypocalcaemia and elevated PTH-consistent with secondary hyperparathyroidism-was identified in 13.7% of patients. Participants with elevated PTH had significantly lower hip BMD compared with those without PTH elevation (median -2.3 vs -1.9, p = 0.004). This association remained significant after adjustment for age and sex (β -0.23, 95% CI: -0.45 to -0.01; p = 0.042). In multivariable models, increasing age (β -0.046 per year, 95% CI: -0.063 to -0.029; p < 0.001) and higher PTH levels (β -0.006 per unit, 95% CI: -0.010 to -0.002; p = 0.002) were independently associated with lower hip BMD. In contrast, vitamin D supplementation (β = -0.113, 95% CI -0.493 to 0.266; p = 0.56) and calcium supplementation (β = 0.101, 95% CI -0.556 to 0.758; p = 0.76) were not independently associated with BMD. Living setting was also not independently associated with hip BMD after adjustment (β -0.326, 95% CI: -0.858 to 0.207; p = 0.23). Exploratory analyses suggested a U-shaped relationship between TSH and hip BMD, with both suppressed and elevated TSH levels associated with lower BMD compared with the euthyroid range. CONCLUSION: Severe vitamin D deficiency is common in very old hospitalized patients and frequently coexists with hypocalcaemia and secondary hyperparathyroidism. Elevated PTH levels are independently associated with lower hip bone mineral density, highlighting the importance of evaluating the calcium-vitamin D-PTH axis. Both suppressed and elevated TSH levels were associated with lower BMD. These findings underscore the need for comprehensive endocrine assessment of bone health in geriatric patients.