CYP27B1 and periodontitis: Reasons for the higher expression of CYP27B1 in the periodontitis group might be as follows: (1) 25OHD3 is an up-regulator of CYP27B1 in hGFs (Gao, Liu & Meng, 2018), and 25OHD3 levels in gingival crevicular fluids of patients with periodontitis before initial periodontal therapy were significantly higher than those after therapy (Liu et al., 2010); (2) Periodontal inflammation results in higher concentrations of IL-1 β and butyric acid in gingival crevicular fluids (Liu et al., 2010; Lu et al., 2014), which also induces the expression of CYP27B1 in hGFs (Liu, Meng & Hou, 2012b).