This is the first study to examine the use of a health assets index in a hospital population. Hospitalisation is a critical juncture for older adults and as frailty does not explain all variation in outcomes, improving prognostication could have great benefits to individuals and hospital systems. This study demonstrates a significant interaction between health assets and frailty and provides insights into both the development and management of frailty. Among these older inpatients, a higher score on the HAI was associated with an improved baseline health status, as evidenced by the lower likelihood of frailty. The HAI alone was not predictive of mortality or functional decline, but in a model that accounted for the interaction with frailty it had differing effects for more robust compared to more frail older adults. This suggest that health assets are likely to moderate the development of frailty and to mitigate adverse outcomes for more robust older adults.
In studies of older adults, frailty alone is a better predictor of mortality than age alone.13 As not all older adults become frail at the same rate, with population ageing, it is important to develop a better understanding of factors that influence the development of frailty.14 The inverse proportional relationship between a higher number of health assets and frailty is in keeping with other studies indicating that psychosocial factors through life affect health status in older age.15 This highlights the importance of taking a life course approach to understanding ageing.
One of the strengths of the frailty index is that it utilizes a multidimensional approach to frailty, which incorporates physical, cognitive and functional components, which are all components of a comprehensive geriatric assessment.16
The concept of health assets was first developed and explored in the community setting in longitudinal studies.5,7 The lack of impact of protective factors for those who were already frail is consistent with findings in the community and supports that once an individual is frail, protective factors do not improve survival. 8 The Canadian Study of Health and Aging has also demonstrated that for adults aged 65 and older who were fit, a higher level of self-rated health, which is a Health Asset, protected against mortality.17 The different effect of Health Assets for those who are robust and frail is likely related to the underlying physiological differences between these groups. It may be that when someone is extremely frail, the allostatic load leads to a critical loss of physiological reserve, so that any biological impact of protective factors is negated.17
It is not clear why the higher number of health assets would be associated with a higher mortality for people who are very frail. Those with a higher number of health assets may be better supported in the community, and only present to hospital with a more significant illness. Conversely it is also possible that this frail group are particularly dependent on their assets, such as carers and emotional support, and are at greater risk when they cannot access these.
The lack of a clear proportional relationship between health assets and mortality contrasts with other studies in the hospital setting.9 Although many studies have identified an association between individual assets and improved outcomes, most of these studies did not include a measure of frailty. Multiple studies investigated mortality and functional decline up to a year after discharge from hospital, and so it may be that health assets have more impact over the months following discharge.18
This differing effect of health assets on older adults depending on frailty status indicates a challenge with measuring health assets. Although individual assets may have varying effects for individuals, the advantage of measuring multiple assets is that it the higher overall score is associated is associated with a lower level of frailty, somewhat mitigating individual variation.
Although frailty is mostly defined in physiological terms as a loss of homeostatic reserve, and is characterized by a stochastic accumulation of subcellular deficits, the impact of psychosocial factors on biology needs to be considered as part of the pathogenesis. In longitudinal community studies, a higher number of social supports are protective for older adults, when accounting for frailty and co-morbidity.6,19 Mechanistically there is evidence that negative psychosocial factors are associated with higher levels of inflammation, which is a proposed mechanism of accelerated biological ageing and the development of frailty.20,21 It may be that a higher number of Health Assets can buffer these changes, which is why it is associated with a better health status.
In this cohort, frailty was not predictive of mortality, functional decline or length of stay, which contrasts with previous studies in the hospital setting.1,22 A recent review identified that 25% of studies in the hospital setting, increasing frailty is not predictive of mortality.23 This is in contrast studies where frailty is measured in the community setting.13,24 This highlights the need for further implementation work in the clinical setting to better determine how this score improves risk prediction for individuals. It also highlights the importance of utilizing data that has been collected in the community setting for hospital based risk prognostication.
Sarcopenia is a loss of muscle strength and function. This is highly prevalent in populations of older adults admitted to hospital, with prevalence at around 35%.25 Sarcopenia is strongly associated with frailty and limitation in ADLs.25 Sarcopenia was not measured in this cohort, but it is likely to provide an important contribution to limitations in ADLs identified.
This study also highlights one of the difficulties in measurement of health assets. When a biological measure, such as optimal creatinine, is identified, a laboratory cut off range is chosen by identifying a range that will cover most of the population. For items like social connection, it is not only the frequency, but also the quality of connections that impact health. It may be more appropriate to take a subjective and individualised approach to these items.
The study has certain strengths: very few patients refused participation, and due to the use of routine data, there was a high rate of follow-up for the primary outcomes. There were also important limitations: the relationship between frailty and health assets was only measured at one point in time, so causation cannot be inferred. It is possible that mortality was under-reported as hospital record data was used, along with phone calls to individuals who had returned home, although not all could be contacted. The small sample size meant that there may have been insufficient power to detect a statistically significant result. Due to limited numbers of research personnel, not all possible participants could be approached. The statistical model that utilised an interaction was not pre-specified, so this should be interpreted with caution. People who did not speak English were not included due to the lack of resources for interpreters, which limits generalizability in a multicultural setting. The follow-up was limited to a maximum of 30 days after hospital discharge, but it is possible that over a longer duration of time after discharge, health assets may have an impact on survival. The study took place in an Australian setting, so the HAI may not be valid in other countries.
Further qualitative research specific to older adults could help determine which factors this age group think are desirable and have an immediate impact on their own wellbeing.