Cu to Zn ratio, physical function, disability, and mortality risk in older elderly (ilSIRENTE study)

Associations between copper to zinc ratio (CZr) and mortality have suggested CZr as a biomarker of aging. Nevertheless, very limited data exist on the association between serum CZr and physical or functional status of very old people. We examined the relationship between serum CZr and physical performance, muscle strength, functional status, and survival from the ilSIRENTE Study: a longitudinal study of persons aged 80 years or older (n = 346). An adjusted linear regression model was subsequently performed to calculate the regression coefficients of the associations between baseline physical and functional measures (dependent variable) with CZr or "Cu and Zn" alone taking also into account the influence of other relevant factors, including hematological (albumin, cholesterol, and urea) and inflammatory biomarkers (IL-6 and CRP) that were significantly different across CZr tertiles. CZr showed significant and stronger relationships than Cu or Zn alone with all baseline physical and functional measures in models that did not include adjustments for inflammatory parameters. CZr was also associated with physical decline, measured as "SPPB% decline" at 2 years of follow-up and mortality at 4 years of follow-up. Subjects in the high CZr tertile had a higher risk of death with an adjusted hazard ratio of 1.92 (95% CI, 1.12-3.29; p = 0.02). In conclusion, we have confirmed the role of CZr as a predictor of mortality, whereas the role of CZr as a biomarker or predictor of physical or functional performance seems to be the consequence of its strict relationships with inflammatory parameters. In this context, further investigations need to be carried out.