Frailty, fitness and late-life mortality in relation to chronological and biological age.

Arnold B Mitnitski,Janice E Graham,Alexander J Mogilner,Kenneth Rockwood

doi:10.1186/1471-2318-2-1

Arnold B Mitnitski, Janice E Graham + Show 2 more

Open Access

https://doi.org/10.1186/1471-2318-2-1

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Abstract

BackgroundPeople age at remarkably different rates, but how to estimate trajectories of senescence is controversial.MethodsIn a secondary analysis of a representative cohort of Canadians aged 65 and over (n = 2914) we estimated a frailty index based on the proportion of 20 deficits observed in a structured clinical examination. The construct validity of the index was examined through its relationship to chronological age (CA). The criterion validity was examined in its ability to predict mortality, and in relation to other predictions about aging. From the frailty index, relative (to CA) fitness and frailty were estimated, as was an individual's biological age.ResultsThe average value of the frailty index increased with age in a log-linear relationship (r = 0.91; p < 0.001). In a Cox regression analysis, biological age was significantly more highly associated with death than chronological age. The average increase in the frailty index (i.e. the average accumulation of deficits) amongst those with no cognitive impairment was 3 per cent per year.ConclusionsThe frailty index is a sensitive predictor of survival. As the index includes items not traditionally related to adverse health outcomes, the finding is compatible with a view of frailty as the failure to integrate the complex responses required to maintain function.

Highlights

People age at remarkably different rates, but how to estimate trajectories of senescence is controversial
The logarithm of the ratio ln(f) may be considered as an appropriate index of relative frailty/fitness; a positive value of the logarithm indicates frailty, whereas a negative value indicates fitness. (When relative fitness/frailty is to be measured as a dichotomous variable, the mean case is taken as fit; i.e. f < 1.) Figure 3 presents the proportion of fit and frail people who survive, averaged by 5-years intervals
We have extended an earlier conceptualization of functional age [10] to present a method of estimating personal biological age, and from that, to estimate relative fitness and frailty

Summary

Introduction

People age at remarkably different rates, but how to estimate trajectories of senescence is controversial. How best to summarize this variability in impairments is not clear. While functional disabilities tend to follow a hierarchical pattern, [2,3,4] summarizing disabilities without reference to the associated illnesses omits important information. With a more rigorous theoretical base, such as frailty [1] and allostatic load [5], have been proposed as a better means of assessing the heterogeneity of health status amongst elderly people, but none has yet proved entirely satisfactory [6,7,8,9]. We recently proposed that the concept of functional age can be derived from a representative database which includes information on a range of variables [10]. We identified a constellation of signs and symptoms from (page number not for citation purposes)

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