Circulating α-Klotho and Multidimensional Aging and Frailty Outcomes: A Systematic Review and Meta-Analysis from the European Renal Association CKD-MBD Working Group.

= 100%). Lower circulating α-Klotho levels were observed in individuals with osteoporosis compared with those with normal BMD (95% CI: - 114.98, - 25.49; p = 0.002) and in individuals with osteopenia compared with those with normal BMD (95% CI: - 123.22, - 0.74; p = 0.05), and were associated with fractures. Based on qualitative synthesis, circulating α-Klotho levels were positively associated with multiple physical function outcomes, including grip strength, short physical performance battery scores, and sit-to-stand performance, with mixed findings for gait speed and the 6-min walk test. Circulating α-Klotho appears to be a promising biomarker for frailty, physical function, and bone health in aging; however, evidence for cognitive outcomes remains limited and inconsistent. Substantial heterogeneity and the observational nature of most studies highlight the need for more standardized and longitudinal research.