Hypovitaminosis D and parathyroid hormone response in the elderly: effects on bone turnover and mortality

Abstract

Objective: To investigate whether absence of secondary hyperparathyroidism in the presence of hypovitaminosis D has altered bone turnover, fracture risk and mortality.

Design: A prospective cohort study.

Patients: A total of 1280 older men and women living in residential care facilities.

Measurements: We measured baseline serum 25-hydroxyvitamin D (25OHD), serum intact PTH, serum amino-terminal propeptide of type I collagen (PINP) and serum carboxy-terminal telopeptide of type I collagen (CTX-I). Deaths and fractures were recorded prospectively.

Results: Hypovitaminosis D (25OHD < 39 nmol/l) and absence of secondary hyperparathyroidism (PTH > 7.0 pmol/l) in the presence of hypovitaminosis D were common in this sample with a prevalence of 77.5% and 53.3%, respectively. In the presence of hypovitaminosis D, residents showing a hyperparathyroid response (n = 406) had significantly higher serum bone turnover markers than individuals with serum PTH levels < or = 7.0 pmol/l (termed 'low vitamin D, normal PTH', n = 463). After adjusting for risk factors, mortality was significantly higher in the secondary hyperparathyroidism group than in the 'low vitamin D, normal PTH' group [hazard ratio (HR) = 1.35, 95% confidence interval (CI) 1.12-1.64; P = 0.002]. All residents with serum PTH levels < or = 7.0 pmol/l (n = 603) were similar with regard to both bone turnover and mortality, independent of their actual vitamin D status.

Conclusion: Absence of secondary hyperparathyroidism in the presence of hypovitaminosis D appears to be common in the frail elderly and is associated with longer survival, similar to that observed in vitamin D-replete elderly subjects.