Low serum vitamin D is associated with higher cortical porosity in elderly men

Background: Bone loss at peripheral sites in the elderly is mainly cortical and involves increased cortical porosity. However, an association between bone loss at these sites and 25‐hydroxyvitamin D has not been reported. Objective: To investigate the association between serum levels of 25‐hydroxyvitamin D, bone microstructure and areal bone mineral density (BMD) in elderly men. Methods: A population‐based cohort of 444 elderly men (mean ± SD age 80.2 ± 3.5 years) was investigated. Bone microstructure was measured by high‐resolution peripheral quantitative computed tomography, areal BMD by dual‐energy X‐ray absorptiometry and serum 25‐hydroxyvitamin D and parathyroid hormone levels by immunoassay. Results: Mean cortical porosity at the distal tibia was 14.7% higher (12.5 ± 4.3% vs. 10.9 ± 4.1%, P < 0.05) whilst cortical volumetric BMD, area, trabecular bone volume fraction and femoral neck areal BMD were lower in men in the lowest quartile of vitamin D levels compared to the highest. In men with vitamin D deficiency (<25 nmol L−1) or insufficiency [25–49 nmol L−1, in combination with an elevated serum level of parathyroid hormone (>6.8 pmol L−1)], cortical porosity was 17.2% higher than in vitamin D‐sufficient men (P < 0.01). A linear regression model including age, weight, height, daily calcium intake, physical activity, smoking vitamin D supplementation and parathyroid hormone showed that 25‐hydroxyvitamin D independently predicted cortical porosity (standardized β = −0.110, R2 = 1.1%, P = 0.024), area (β = 0.123, R2 = 1.4%, P = 0.007) and cortical volumetric BMD (β = 0.125, R2 = 1.4%, P = 0.007) of the tibia as well as areal BMD of the femoral neck (β = 0.102, R2 = 0.9%, P = 0.04). Conclusion: Serum vitamin D is associated with cortical porosity, area and density, indicating that bone fragility as a result of low vitamin D could be due to changes in cortical bone microstructure and geometry.