Functional Impairment in Aging Correlates with Mortality Risk
Aging is an accumulation of cell and tissue damage, combined with the dysfunctions resulting from that damage. Damaged systems lose function in a haphazard, random fashion that, averaged out over time and across many systems, tends to be proportional to the burden of damage. This is the case whether the system is a simple mechanical device, an organ, or a human. In aging humans and animals one thus observes correlations between most different examples of lost and degraded function, including those that cause mortality.
We assessed the population distribution of age-related functional impairments (ARFIs) and their associations with mortality and life expectancy (LE). We included 12,906 participants (mean age: 62.6 years) from the China Health and Retirement Longitudinal Study. Visual impairment, hearing impairment, cognitive impairment, sleep disorder, depressive symptoms, and disability in activities of daily living (ADL) were assessed. Cox proportional hazards models were used to estimate the associations of ARFIs with all-cause mortality. Life expectancy at age 50 was estimated by the presence and number of key ARFIs.
The six ARFIs exhibit distinct distributions by ages and provinces across China. During the 9-year follow-up, ADL disability, cognitive impairment, and depressive symptoms are independently associated with 64%, 41%, and 20% higher risks of mortality, corresponding to LE losses of 4.45, 3.08, and 1.59 years at the age of 50 years. A greater number of key ARFIs is associated with higher mortality risk in a dose-response manner (hazard ratios: 1.23 for one, 1.42 for two, and 1.86 for three) and greater LE loss (1.63 years for one, 3.37 for two, and 4.96 for three).