Vitamin D status affects serum parathyroid hormone concentrations during winter in female adolescents: associations with forearm bone mineral density

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Abstract
Background: Vitamin D deficiency leads to secondary hyperparathyroidism, which has a negative effect on bone metabolism in the elderly. Puberty is an important time of bone metabolism and growth. The effect of serum 25-hydroxyvitamin D [25(OH)D] concentrations on parathyroid hormone concentrations and bone mineral density (BMD) has not been well studied cross-sectionally in adolescents. Objective: We studied the effect of vitamin D status on serum intact parathyroid hormone (iPTH) concentrations and bone metabolism in adolescents. Design: One hundred seventy-eight healthy female adolescents (aged 14–16 y) volunteered for this study, which was conducted in Finland (Helsinki, 60°N) during the winter. Forearm BMD at radial and ulnar sites was measured by dual energy X-ray absorptiometry. The determinants of different variables were studied by use of regression models. Results: On the basis of the relation between serum 25(OH)D and iPTH concentrations, serum 25(OH)D concentrations >≈40 nmol/L were needed to keep serum iPTH concentrations low. One hundred ten subjects (61.8%) had serum 25(OH)D concentrations ≤40 nmol/L. Twenty-four subjects (13.5%) were considered vitamin D deficient when the serum 25(OH)D concentration of 25 nmol/L was used as a cutoff. Subjects with serum 25(OH)D concentrations ≤40 nmol/L had low mean forearm BMD values at both the radial (P = 0.04) and ulnar (P = 0.08) sites. Conclusion: A large percentage of adolescent females have low vitamin D status during the winter in Finland, which seems to have negative effects on bone health.