Lower serum 25-hydroxyvitamin D is associated with increased bone resorption markers and lower bone density at the proximal femur in normal females: a population-based study.

Subclinical vitamin D deficiency is considered to be a risk factor for osteoporosis. Therefore, we studied vitamin D status and bone mineral density (BMD) in an age- and sex-stratified population based sample (209 males and 206 females aged between 50 and 80 years). In addition, urinary excretion of pyridinium crosslinks of collagen was determined in order to monitor bone resorption. We found a seasonal variation of serum 25-hydroxyvitamin D (25(OH)D) levels with higher values detected in the summer (27 +/ - 10 ng/ml) and lower values measured in the winter (17 +/- 9 ng/ml). Further analyses were performed separately for winter and summer, respectively. We also excluded subjects taking osteotropic medication. In men, we found no significant relationship between vitamin D status and bone density or pyridinium crosslinks. In women, we found significant positive correlations between 25(OH)D and proximal femur BMD in winter (r = 0.21, p < 0.05) and in summer (r = 0.36, p < 0.01). The association between 25(OH)D and proximal femur BMD persisted after correction for age and body mass index. Serum 25(OH)D and urinary pyridinium crosslinks were inversely correlated in females in winter (r = -0.24, p < 0.02) and in summer (r = -0.32, p < 0.02). Our data support the hypothesis that already moderately low serum levels of 25(OH)D within the "normal" range lead to osteopenia via increased bone resorption.