Almost all approaches to conceptualising successful or positive ageing place considerable emphasis on the importance of health, and the research literature broadly supports this emphasis. In particular, worse functional health and worse self-rated health, have been consistently found to be associated with lower life satisfaction or quality of life (Bowling, Farquhar, & Grundy, 1996; Diener et al., 1999; George, 2010; Pinquart & Sorensen, 2000; J. Smith, Borchelt, Maier, & Jopp, 2002). In addition, disability is predictive of greater depressive symptoms (Ormel & Rijsdijk, 2002; Stegenga et al., 2012).
However, findings in relation to chronic disease are less consistent (Gwozdz & Sousa-Poza, 2009), particularly for the oldest-old (Berg, Hassing, McClearn, & Johansson, 2006). It has been argued that diagnoses may not be a good predictor of wellbeing because of the heterogeneity of health status even across individuals with the same condition (Berg, Hassing, Thorvaldsson, & Johansson, 2011). This was supported by recent evidence from TILDA that suggests that chronic conditions only have a negative effect on emotional wellbeing and quality of life if they are associated with impaired body function (e.g. weaker muscle strength) or activity limitations (e.g. reduced ability to carry out basic activities of daily living) (Sexton, King-Kallimanis, Layte, & Hickey, 2014). This highlights the importance of measuring functional deficits and perceived health as indicators of health, in addition to specific diseases or diagnoses.
In recent years, there has been increasing research interest in the concept of frailty. Frailty is a state of increased vulnerability to stressors, which is brought on by age-related decline across physiological systems (Clegg, Young, Iliffe, Rikkert, & Rockwood, 2013). Frail older adults are more likely to suffer major health effects as a result of a relatively minor health problem, such as a minor infection. Current evidence suggests that approximately one in 10 adults aged 65 and over are physically frail (Collard, Boter, Schoevers, & Oude Voshaar, 2012) , and that these adults are at a higher risk for falls, disability, hospitalisation, nursing home admission and death (Clegg et al., 2013).
Cognitive decline is strongly associated with increasing age, and maintaining cognitive function is also considered a critical part of healthy ageing. Cognitive function and dementia have been identified as key risk factors for the onset of disability and reduced physical function in later life (Spiers et al., 2005). However, evidence for the association between cognitive function and wellbeing outcomes is mixed. A number of studies found that cognitive decline was not associated with lower life satisfaction or higher risk of depression (Gerstorf, Lövdén, Röcke, Smith, & Lindenberger, 2007; Gow et al., 2005). However, there is some evidence that cognitive decline, particularly in the area of executive function, has a negative effect on dimensions of wellbeing related to purpose and personal growth (Allerhand, Gale, & Deary, 2014; Wilson et al., 2013).
There is also evidence that older adults can adapt to disability, maintaining their subjective wellbeing as physical health declines. Oswald & Powdthavee (2008) found evidence that people adapt to disability, with the negative impact of the disability on life satisfaction reducing over time. However, life satisfaction did not fully recover to the same level as before disability onset (Oswald & Powdthavee, 2008). The extent to which someone adapts to disability may depend on a person’s level of resilience, which can depend on factors specific to the person and their contextual circumstances (Smith & Hayslip, 2012). Resilience is an important characteristic for all people but can be particularly so for older people as the ability to recover from negative life events (such as ill-health or death of friends or partner) becomes more necessary.