The systematic review by Mello et al. (p. 1143) provides evidence of the consistency of the association between physical frailty and major socioeconomic factors such as income and degree of schooling. Their work is an important reminder of how social determinants influence the way populations age. Only recently delegates of several professional and scientific societies dedicated to the study of aging arrived at a consensus over the concept of physical frailty in older people as “a medical syndrome with multiple causes and contributors that is characterized by diminished strength, endurance, and reduced physiologic function that increases an individual’s vulnerability for developing increased dependency and/or death” (Morley et al. J Am Med Dir Assoc 2013; 14:392-7).

But what is the importance of the concept for Public Health? My perspective is that the idea of physical frailty helps us to think of the process of biological aging more clearly and beyond simple chronological aging. Aging is heterogeneity. No other age group displays such high variability among its members regarding functional status, burden of comorbidities and other characteristics, as do older adults. Prior to the emergency of the concept of frailty that heterogeneity was mostly understood in terms of functional status, degrees of dependency versus independency and comorbidities. It was almost as if the whole underwater part of the iceberg of aging had been disregarded – where subclinical physiological changes that decrease the ability to maintain homeostasis when facing different stressors hide. Indeed the very decline of physiological reserves is the hallmark of biological aging. As a corollary we can conceptualize frailty as a clinical marker of biological age and aging. This point of view unveils several new possibilities for research and action. First, it assuages the inexorability of chronological aging and shares, at least partially, with individuals and society the reins of biological aging. To prevent or reverse the development of frailty through the practice of exercise and the adoption of a healthy lifestyle would be analogous to keeping young biologically. This idea is consistent with the results of a recent study that showed that comprehensive lifestyle changes are able to increase the size of telomeres (Ornish et al. Lancet Oncol 2013; 14:1112-20) – another marker of biological age. This would be comparable to “rewinding” the biological clock of individuals. Second, it could turn out to be a potent means of influencing positive changes in lifestyle within populations. For instance, there is evidence that telling smokers about their “lung age” can double the proportion of smokers that quit (Parkes et al. BMJ 2008; 336:598-600). Lastly, the notion of physical frailty broadens the possibilities to develop preventive health strategies towards the goal of “compression of morbidity”, where the increases in longevity of populations is followed by decreases in the frequency or a delay in the occurrence of functional dependence (Fries et al. J Aging Res 2011; 2011:261702).

To consider physical frailty in terms of its social determinants, as indicated by the work of Mello et al., strengthens the case for public policies aimed at decreasing social inequities as a means to promote healthy and active aging across populations. Future systematic reviews concerning the social determinants of physical frailty in the elderly should provide quantitative syntheses about the strength of the associations found and encompass other diagnostic criteria for frailty. Finally, it must be emphasized that the concepts of psychological and social frailty remain unconcluded, leaving major knowledge gaps and fertile soil for future approaches and investigations in the field of Public Health.

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