Abstract
BACKGROUND: The aging-suppressor gene klotho encodes a single-pass transmembrane protein that in mice is known to extend life span when overexpressed and resemble accelerated aging when expression is disrupted. It is not known whether there is a relationship between plasma levels of secreted klotho protein and longevity in humans. METHODS: We measured plasma klotho in 804 adults, greater than or equal to 65 years, in the InCHIANTI study, a longitudinal population-based study of aging in Tuscany, Italy. RESULTS: During 6 years of follow-up, 194 (24.1%) of the participants died. In a multivariate Cox proportional hazards model, adjusting for age, sex, education, body mass index, physical activity, total cholesterol, high-density lipoprotein cholesterol, cognition, 25-hydroxyvitamin D, parathyroid hormone, serum calcium, mean arterial pressure, and chronic diseases, participants in the lowest tertile of plasma klotho (<575 pg/mL) had an increased risk of death compared with participants in the highest tertile of plasma klotho (>763 pg/mL; hazards ratio 1.78, 95% confidence interval 1.20-2.63). CONCLUSIONS: In older community-dwelling adults, plasma klotho is an independent predictor of all-cause mortality. Further studies are needed to elucidate the potential biological mechanisms by which circulating klotho could affect longevity in humans.