The goal of this study was to evaluate the relationship of 25-hydroxyvitamin D concentration with the incidence of major clinical disease events that are pathophysiologically relevant to vitamin D. Participants were 1621 white older adults.  The authors found that the threshold concentrations of 25-(OH)D associated with increased risk for relevant clinical disease events center near 50 nmol/L (20 ng/mL).

http://www.annals.org/content/156/9/627.long

Thickening of the femoral shaft cortical bone has been mentioned in reports of atypical subtrochanteric and diaphyseal (S/D) femur fractures.  These authors examine the relationship of cortical thickness to S/D fracture risk in a large cohort of older women.  However they found no evidence that thick femoral cortices placed women at higher risk for low-energy S/D femur fractures; in fact, the opposite was true. Women with thin cortices were at a higher risk for femoral neck and intertrochanteric fractures.

http://www.ncbi.nlm.nih.gov/pubmed/22547423