Frailty: The Broad View

Frailty

To better appreciate the heterogeneous health status of the older persons, the frailty concept was introduced in geriatric and gerontology literature about 20 years ago. Frailty is now noncontroversially understood as the concept of increased vulnerability to adverse outcomes among people of the same chronologic age. It is the term used to indicate the geriatric syndrome or state characterized by a reduction of the organism's homeostatic reserves. The lower capacity of the organism to face entropic forces (coming from endogenous and exogenous sources) exposes an individual to an increased risk of negative health-related events, including falls, hospitalizations, worsening disability, institutionalization, and mortality. In a frail individual, a clinically irrelevant endogenous or exogenous stressor may become the trigger for the initiation of the burdening disabling cascade.

Frailty has been defined by an international consensus of experts as “a multidimensional syndrome characterized by decreased reserve and diminished resistance to stressors.” A widely accepted definition of frailty was provided in Orlando, Florida, by an international consensus group in 2012. It stated that frailty is “a medical syndrome with multiple causes and contributors that is characterized by diminished strength, endurance, and reduced physiologic function that increases an individual's vulnerability for developing increased dependency and/or death.”

In a recent review paper, Clegg and colleagues clearly depicted frailty not as a syndrome but as a state of vulnerability that challenges the maintenance of homeostasis in older persons. Similarly, the deficit accumulation approach sees frailty as a multidimensional risk state that can be measured by the quantity rather than by the nature of health problems. This approach proposes that frail older adults have many things wrong with them; the more things they have wrong, the higher the likelihood that they will be frail and the greater their risk of adverse health outcomes. Based on this definition, frailty arises from a multisystem decline, which compromises the body's ability to repair damage that arises externally or as the byproduct of internal processes, (e.g., metabolic, respiratory, inflammatory), including genetically induced damage.

However, frailty is not all or none; grades of frailty make a difference. Still, many studies classify people simply as frail or nonfrail. In some settings, such as comparing frailty prevalence in different samples, this can be useful; however, even in this case, important information gets lost. Many clinical decisions require greater precision than a nonfrail-frail status. In addition, frailty is a dynamic process where transitions across states of frailty are common. On average, health tends to decline with age, and the population-based trajectories of frailty are consistent, showing acceleration in deficit accumulation. The frailty index increases, on average, tenfold between 20 and 90 years. Even so, individual trajectories of the frailty index are generally irregular, showing that frailty reflects a stochastic dynamic process. For an individual, most transitions are gradual, and the likelihood to change their frailty level is largely conditioned on their previous frailty level. Therefore, transitioning from a nonfrail state to a severely frail state (and vice versa) is not very common. In individuals, including older adults, frailty levels increase nonmonotonically over time; however, health status can improve, which will result in a transition from a higher to a lower frailty level state.

In a study conducted by Gill and associates, nondisabled subjects aged 70 years and older were followed over time to monitor changes in their frailty status. Among the 754 participants, more than half (57.5%) experienced at least one transition across any of the frailty states during the 54-month follow-up period. It was also reported that 44.3% of robust participants at the baseline transitioned to a prefrailty (40.1%) or frailty (4.2%) condition during the first 18 months of follow-up. Among participants presenting as frail at baseline, most (63.9%) remained frail, whereas 23.0% improved to a healthier condition, and 13.1% died. Consistent results showing the positive and negative changes of the frailty condition over time have also been reported in data collected as part of the Survey of Health, Ageing, and Retirement in Europe (SHARE). Recent studies have started exploring which conditions may be associated with improvement or worsening of the frailty condition. For example, Lee and coworkers reported the significant association of specific characteristics with negative modifications (e.g., older age, history of cancer, hospitalization events, chronic obstructive pulmonary disease, cerebrovascular disease, osteoarthritis) and positive modifications (e.g., higher cognitive function, absence of diabetes, higher socioeconomic status, no history of cerebrovascular disease) across frailty states. Even though these characteristics can accelerate frailty, typically frailty develops slowly, even insidiously, and can vary in important ways among individuals.

It is well established that although they frequently coexist in the older person, frailty, comorbidity (the concurrent presence of two or more medically diagnosed diseases), and disability (the difficulty or dependency in carrying out activities of daily life) are distinct conditions. For example, in the Cardiovascular Health Study, Fried and colleagues reported that comorbidity, disability, and the two together coexist in 67.7%, 27.2%, and 21.5% of frail participants, respectively. On the other hand, people who meet the criteria for the frailty might do so in the absence of comorbidity and disability, as reported in 26.6% of cases in the same study.

Recently, the concept of “resilience” (the individual's ability to adapt in the face of stresses and adversities) has become increasingly used in parallel with frailty. Although resilience is still is not adequately framed and defined, it is possible that it might be a field of promising research in the near future. Low versus high resilience may indeed make a difference and explain why individuals with the same frailty status follow opposite trajectories (i.e., toward disability and robustness, respectively). Although resilience is still only a briefly stated concept, its quantification may provide important insights in the assessment of the older person's risk profile. As with the frailty syndrome, resilience also results from the complex network of biologic, clinical, social, and environmental factors characterizing each individual. We also need to consider that some degree of variability in health outcomes is to be expected in relation to frailty. Some people who are severely frail can survive in highly protective environments, whereas some nonfrail people will die. This could be related to the degree of damage to which an individual is exposed or to the resources available to assist with the repair of that damage. Even in Canada, a higher income country with a universal health care system, among individuals who are considered the fittest (lowest level of frailty), 5-year mortality is doubled among those classified with high social vulnerability levels compared to those with the lowest social vulnerability levels.