Physiological redundancy in older adults in relation to the change with age in the slope of a frailty index

Objectives: To test the proposition, using routinely available clinical data, that deficit accumulation results in loss of redundancy. In keeping with the reliability theory of aging, this would be quantitated by attenuation in the slope of a Frailty Index (FI) with age. The more deficits, the less steep the slope and the less redundancy. Design: Cross-sectional analysis of a prospective cohort study, with 5-year mortality data. Setting: The clinical sample of the second wave of the Canadian Study of Health and Aging. Participants: Two thousand three hundred five people aged 70 and older at baseline. Measurements: A FI based on data used for a Comprehensive Geriatric Assessment (CGA), the slope of the relationship between age and the FI-CGA, the limit value of the FI-CGA, mortality. Results: An age-invariant limit to deficit accumulation was demonstrated; the observed 99% limit was 0.66. At the 25th percentile of deficit accumulation (FI-CGA ∼0.18), the slope of the FI-CGA in relation to age was 0.044 (range 0.038-0.049). When deficits had increased to 75% of the maximum value (FI-CGA ∼0.52), the slope fell to 0.021 (range 0.016-0.027). By the 85th percentile (FI-CGA ∼0.6), the slope had become statistically indistinguishable from 0. Conclusion: As predicted by the reliability theory of aging, the rate of deficit accumulation slows with increasing frailty. A FI derived from data routinely collected as part of a CGA can in this way quantify loss of redundancy in older adults. Quantifying loss of redundancy can aid clinical decision-making; its application to individual prognostication in clinical samples warrants further evaluation.