CYP27A1 and osteoporosis: Exposure to high-altitude hypoxia also resulted in lower values in bone formation bio-markers, including bone alkaline phosphatase (BALP), propeptide of type I procollagen (PINP), and bone gla-protein (BGP) in mice, while the bone resorption bio-marker cross-linked with C-telopeptide of type I collagen (CTX) was higher, leading to the occurrence of osteoporosis.