Response to Vidal and colleagues.

Abstract

To the Editor: We thank Vidal and colleagues for their comments on our recent article on frailty and oxidative stress.1 We agree that oxidative stress correlates with biological age and not with chronological age. Frailty has become a highly interesting area of geriatrics and is related to biological aging. We agree with Vidal and colleagues that it is advisable to start thinking about aging in terms of biological rather than chronological age, but the free radical theory of aging in its strict formulation (as we stated in our paper) relates chronological aging to the damage associated with free radicals. Let us underpin the critical importance of the work of Denham Harman2 in formulating the free radical theory of aging. We recently reviewed theories of aging3 and formulated a modified free radical theory of aging.4 In spite of all this, we agree with Vidal and colleagues that our findings do not contradict the free radical theory of aging insofar as frailty can be considered a biomarker of aging. Regarding their interest in the variables included in the multivariate linear regression models we used to analyze the relationship between oxidative stress and frailty, we used different models for lipid peroxidation (determined as malondialdehyde formation from these peroxides) and protein carbonylation. For malondialdehyde levels, the included variables were age, sex, frailty status, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol, and triglycerides in the first model, with the addition of aspartate amino transferase, alanine amino transferase, gamma-glutamyl transferase, alkaline phosphatase, and lactate dehydrogenase in the second model. For protein carbonylation, the variables included were age, sex, frailty status, albumin, and serum total protein. Finally, we want to thank Vidal and colleagues again for their interest in our work and for highlighting the importance of biological aging and its relationship with good physical and mental health. Oxidative stress is directly related to frailty, eventually leading to dependence, a condition that we must try to prevent by all means. This work was supported by Grants SAF2010–19498, from the Spanish Ministry of Education and Science (MEC); ISCIII2006-RED13–027 and ISCIII 2012-RED-43–029 from the Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad; PROMETEO2010/074 from Conselleria d'Educació, Cultura i Esport de la Generalitat Valenciana; 35NEURO Gentx Gent from Fundació Gent Per Gent de la Comunitat Valenciana; Intramural Grant RS2012–609 from the Fundación Investigación Clínico de Valencia and CM1001; and FRAILOMIC-HEALTH.2012.2.1.1–2 from the European Union. This study was co-financed with European Fund for Economic and Regional Development funds from the European Union. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Viña, Inglés and Borrás: writing the manuscript. Sponsor's Role: The sponsor had no role in the design, methods, subject recruitment, data collections, analysis, or preparation of the manuscript.