Low Plasma Klotho Concentrations and Decline of Knee Strength in Older Adults.

BACKGROUND: Although the "anti-aging hormone" klotho is associated with sarcopenia in mice, the relationship between klotho and muscle strength in older adults is not well known. METHODS: Plasma klotho concentrations were measured in 2,734 older adults, aged 71-80 years, who participated in the Health, Aging and Body Composition Study, a prospective observational cohort study conducted in Memphis, TN and Pittsburgh, PA. Knee extension strength was measured using isokinetic dynamometry at baseline and follow-up 2 and 4 years later. Knee extension strength was normalized for weight. RESULTS: At baseline, participants in the highest tertile of plasma klotho had higher knee extension strength (β = .72, standard error [SE] = .018, p < .0001) compared with those in the lowest tertile in a multivariable linear regression model adjusting for age, sex, race, smoking, study site, C-reactive protein, interleukin-6, and diabetes. Participants in the highest tertile of plasma klotho at baseline had less of a decline in knee strength over 4 years of follow-up (β = -.025, SE = .011, p = .02) compared with those in the lowest tertile in a multivariable linear regression model adjusting for the same covariates above. CONCLUSIONS: Plasma klotho concentrations were an independent predictor of changes in knee strength over time in older adults. Further studies are needed to identify the biological mechanisms by which circulating klotho could modify skeletal muscle strength.