Multiple linear regression (stepwise regression) analysis showed that compared with stage I/II periodontitis, serum α-Klotho levels were significantly negatively associated with stage III periodontitis (B ± SE = -37.28 ± 16.00, 95% CI: -68.66 to -25.91, P = 0.020) and stage IV periodontitis (B ± SE = -69.37 ± 16.11, 95% CI: -100.97 to -37.77, P < 0.001) (Table 2). Here, KL is linked to periodontitis.