Defining successful aging: the need to distinguish pathways from outcomes

Motivated by a vision for a new gerontology that focuses on optimal functioning rather than losses and declines, Rowe and Kahn (1987) argued that many of the age-related declines that define usual aging are due to modifiable factors such as diet, exercise, personal habits such as smoking, and psychosocial factors. Thus, individuals may engage in lifestyle modifications to avoid diseases and, consequently, enhance their chance of aging well. Three domains of outcomes were said to jointly define successful aging: (a) low probability of disease and disease-related disability, (b) high cognitive and physical functioning, and (c) engagement with life (namely in the form of social connectedness and productive activities; Rowe and Kahn, 1997). All three criteria are meant to be relative (i.e. without absolute thresholds), although subsequent studies tend to adopt a threshold approach (see Depp and Jeste, 2006). The three criteria are somewhat hierarchical, in that avoiding diseases (and associated risk factors) makes high physical and cognitive functioning possible, which in turn enables the individual to engage in social and productive activities (Rowe and Kahn, 1997). However, remaining free of disease/disability and maintaining high physical and cognitive functioning are less likely as one ages, whereas participation in social and even productive activities may not be affected until significant physical and cognitive declines have occurred (McLaughlin et al., 2010; Yaffe et al., 2010; Hsu and Jones, 2012).