Effects of a functional milk powder supplemented with rhizoma drynariae extracts on bone health in growing and ovariectomized rats: More effective for lumbar vertebrae?

Bone health is vital through all life stages and has become a growing public health concern. The role of rhizoma drynariae (RD) as a traditional Chinese medicine for bone injury recovery has been widely investigated. Still, there is little research related to RD as a functional component in food to improve calcium bioavailability and bone health. Milk powder is a daily vital food source of dietary calcium. The present study aimed to investigate and compare the effects of a functional milk powder reinforced with RD extracts (RDE) or vitamin D, vitamin K, and calcium, or both, using Sprague-Dawley rats, with both low calcium growing rat model and low calcium ovariectomized (OVX) rat model. For growing rats, RDE increased bone mineral density (BMD) and improved the microstructure of bone trabecula in the femur and lumbar vertebrae. The levels of serum bone turnover markers C-telopeptide of type Ⅰ collagen (CTX-I), procollagen type Ⅰ amino-terminal peptide (PINP), and osteocalcin (BGP) were increased with RDE supplementation. The tartrate-resistant acid phosphatase staining suggested a decrease in the number of osteoclasts in the femur. Immunohistochemistry showed that the osteoclast-related protein RANKL was downregulated, and the osteogenic-associated proteins RUNX2 and OSX significantly increased in the lumbar vertebrae. Similarly, in OVX rats, RDE improved BMD and microstructure in lumbar vertebrae, and the levels of CTX-I, PINP, and BGP were also increased. In conclusion, the novel functional milk powder supplemented with RDE facilitated osteogenesis and inhibited osteoclast in rats at both stages, especially with lumbar vertebrae in growing rats. Our findings provide new prospects and a more precise target for enhancing bone health by incorporating RDE as a functional component in milk powder.