  How long people live depends on their health, and how it changes with age.
Individual health can be tracked by the accumulation of age-related health
deficits. The fraction of age-related deficits is a simple quantitative measure
of human aging. This quantitative frailty index (F) is as good as chronological
age in predicting mortality. In this paper, we use a dynamical network model of
deficits to explore the effects of interactions between deficits, deficit
damage and repair processes, and the connection between the F and mortality.
With our model, we qualitatively reproduce Gompertz's law of increasing human
mortality with age, the broadening of the F distribution with age, the
characteristic non-linear increase of the F with age, and the increased
mortality of high-frailty individuals. No explicit time-dependence in damage or
repair rates is needed in our model. Instead, implicit time-dependence arises
through deficit interactions -- so that the average deficit damage rates
increases, and deficit repair rates decreases, with age . We use a simple
mortality criterion, where mortality occurs when the most connected node is
damaged.
