group working part time or in flexible arrangements as a response to the later onset of social security benefits and increased workforce demands.
Recent research, reviewed in some detail in this chapter, indicates that rates of significant functional impairment for older (aged 65+) persons have been generally constant over the past decade after a two-decade period of progressive decline. Results for the “near elderly” are conflicting, probably for methodologic reasons, but there is clear evidence of the deleterious effects of increasing obesity on physical function as well as the well-documented beneficial effects of education and stopping smoking.
Disability, generally defined as a limitation in the capacity to perform a given function, is traditionally considered in the framework of a process of disablement in which specific physiologic and pathophysiologic processes advance over time, resulting ultimately in a disability (Nagi, 1965; Verbrugge and Jette, 1994; Martin, Schoeni and Andreski, 2010). Various points along this spectrum may be identified. For instance the earliest stage is marked by the presence of preclinical markers, such as measures of inflammation or altered physiologic control such as high weight, blood pressure, or cholesterol. These risk factors may be followed by the presence of an identifiable disease, such as arthritis, hypertension, diabetes, heart disease, or peripheral vascular disease, which can progress.
In arthritis, for instance, the earliest clinical signs may be very subtle, though biomarkers can be identified as demonstrating risk. As the disease progresses, one advances from joint stiffness and pain to actual difficulty performing tasks and ultimately to disability.
Reasoning that the same underlying secular changes in lifestyle (smoking cessation, more exercise, public health advances, etc.) and advances in the detection and treatment of disease and physiologic risk factors such as hypercholesterolemia that led to increases in life expectancy would also naturally delay the onset of functional impairment, many expected that increases in life expectancy would be yoked to stasis or reductions in late-life disability, leading to the “compression of morbidity” concept popularized by Fries (1980). The result would be an absolute increase in active life expectancy and a progressively shorter portion of the life span spent disabled. On the other hand, some have argued that technological advances in the treatment of disease might convert some once-fatal illnesses to chronic illnesses, increasing the duration of disability as life expectancy increases.