Laboratory assays
Chemiluminescent immunoassays (CLIA) was used to determine bone turnover markers and other bone specific parameters (based on fasting blood samples). Each immunoassay had an inter-assay coefficient of variation, iCV, of 10%. Specifically, we measured levels of intact parathyroid hormone (iPTH) (Siemens), bone alkaline phosphatase (Roche Diagnostics), amino propeptide of type I collagen (P1NP, Roche Diagnostics), collagen type I C-telopeptide (CTX, Roche Diagnostics), serum 25-hydroxyvitamin D