The restricted cubic splines revealed significant linear associations of serum FGF23 levels and FGF23/α-klotho ratio with T2DM combined with CIMT (P for overall < 0.01; Fig. 2b and h), but no significant association was found between serum α-klotho levels and T2DM combined with CIMT (Fig. 2e). Here, FGF23 is linked to type 2 diabetes mellitus.