CYP27A1 and osteoporosis: Compared to the lowest quartile of serum β-CTX, after multiple adjustments, the third and fourth quartiles of serum β-CTX had an increased risk of low SMI (the third quartile: OR = 5.84, 95%CI = 1.21–28.34, P = 0.028; the fourth quartile: OR = 6.80, 95%CI = 1.38–33.60, P = 0.019) and the fourth quartile of serum β-CTX had an increased risk of osteoporosis (OR = 3.39, 95%CI = 1.20–9.55, P = 0.021) (Table 4).