INTRODUCTION
Frailty is defined as a significant decline in the functional reserve of multiple organ systems and the resultant extreme vulnerability of an individual to endogenous and exogenous stressors (such as infection, injury, surgery, or some medicines), leading to a higher risk of accelerated functional decline and adverse health-related outcomes.
1) The adverse health-related outcomes caused by frailty include falls, delirium, immobility, or disability, and, consequently, hospitalizations, institutionalization, or mortality.
1)
Over the past decade, resilience has increasingly become a focus of research in the behavioral and medical sciences. Frail older adults have a preexisting vulnerability to stressors, often resulting in poor outcomes. However, some people recover rapidly from stressors without such outcomes. These individuals are categorized as resilient. Resilience has been defined in various ways, including the ability to rapidly recover from various stressors.
2) The factors that promote resilience, including physical health, a sense of self, social belonging, self-belief, and altruism, overlap with those that reduce frailty.
3) Therefore, an understanding of resilience may help in the study of frailty. Furthermore, a deeper understanding of why some individuals maintain or regain function following stressors, while others do not, may help identify protective factors and strategies to promote lasting health.
4)
There are two types of resilience. The first is “psychological resilience,” which refers to a person’s ability to adapt well in the face of adversity, trauma, tragedy, threats, or significant sources of stress. The second is “physical resilience,” which focuses on the maintenance or recovery of functions after biomedical or pathological challenges. Physical resilience is presumed to reflect adaptive physiological responses at the level of organs, cells, and molecules of the musculoskeletal, neurological, and immunological systems that support homeostasis under changing conditions.
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Psychological resilience is measured with well-organized standard assessments such as the Brief Resilience Scale (BRS).
6) However, there is no gold standard test for measuring physical resilience.
We hypothesized that the time needed to recover from a common cold could be an indicator of physical resilience, as the immunologic response is one component of physical resilience.
5) A previous study showed that self-reported health was related to the duration of common cold.
7) Therefore, we investigated whether the day(s) required for recovery from common cold could represent physical resilience by comparing this number with BRS scores, physical frailty, and health variables to ensure validity.
RESULTS
The participants were divided into three groups according to the numbers of perceived days required for recovery from common cold (Group 1, 1–4 days; Group 2, 5–7 days; Group 3, ≥8 days) (
Table 1). The mean ages of the three groups did not differ significantly, and the mean age of all subjects was approximately 78 years. Participants in Group 3 (≥8 days for recovery) were more likely to be women (60.8%, p=0.004), sleep less, less physically active, fall more, and have a low EuroQol visual analogue scale (EQ-VAS) score. The BRS scores differed significantly among the three groups (Group 1, 13.29; Group 2, 14.32; Group 3, 15.22; p<0.001). The KFI-PC was higher in Group 3 than in other groups (Group 1, 0.15; Group 2, 0.16; Group 3, 0.17; p=0.034).
Tables 2–
4 show the results of ANCOVA. Model 1 was adjusted for sex, Model 2 was further adjusted for sleep time, Model 3 was additionally adjusted for IPAQ, and Model 4 was additionally adjusted for EQ-VAS scores.
Table 2 shows the differences in BRS scores among the three groups. Even after adjusting for the aforementioned factors, the difference between the three groups was significant in Model 4 (Group 1, 13.55; Group 2, 14.32; Group 3, 14.84; p<0.001).
Table 3 presents the relationships with the number of falls and shows no significant results.
Table 4 shows the results for KFI-PC, in which we observed no significant differences.
The Bonferroni method was used for post-hoc analysis in
Tables 2–
4. In
Table 2, which was related to the BRS score, the differences between Groups 1 and 2 in Models 1, 2, and 3 were significant. The difference between Groups 1 and 3 was also significant after adjusting for all confounding factors. In
Table 3, which represented the number of falls, we observed a significant difference between the groups only for Model 1. We observed no significant difference in KFI-PC.
DISCUSSION
The results of this study showed the association between increased days of recovery from a common cold and lower psychological resilience (BRS score), lower quality of life (EQ-VAS score), and lower physical activity level (IPAQ score). However, we observed no association between recovery days and frailty index and frailty outcomes, such as the number of falls.
It may be not surprising that the number of perceived days required for recovery from a cold was not related to frailty, as frailty refers to a “functionally declined and stressor-vulnerable state,” while physical resilience refers to the ability to recover from stressors. Moreover, several factors influence physical resilience, including both emotional and social as well as physical factors.
13) Previous studies have shown that an individual’s degree of frailty and resilience are not simply opposite concepts.
5) Although there is a conceptual overlap between frailty and resilience, frail individuals tend to have a lower resilience and resilience is a continuous spectrum that can change throughout life. In contrast, frailty often evolves near the end of life and manifests in only a small proportion of older adults.
5) The lack of association between recovery days from cold and frailty outcomes such as the number of falls may be owing to the cross-sectional study design. Thus, longitudinal studies are needed.
Resilience is a dynamic construct that can be ascertained through dynamic stimulation tests. As an alternative approach in an observational study, comparing two measurements—one before and one directly after the stressor—with an outcome is needed.
14) We could not present either way in this study, which can be a limitation of this study. Nonetheless, infection is known to be one of the stressors used to evaluate physical resilience, and recovery trajectories after a recent disease (e.g., influenza) is suggested to be one of the best available assessments of resilience.
14) In a similar approach, we surveyed the recovery time from common cold, and we believe that it could be an indirect marker for physical resilience, at least with respect to immunity. Dynamic resilience measurements (trajectories, stimulus-response tests) are not yet sufficiently robust, but recovery trajectories after a recent disease (e.g., influenza, cardiac decompensation, or chronic obstructive pulmonary disease exacerbation) may be one of the best available examples of resilience assessment.
14) However, the common cold is a milder disease than influenza, and therefore, the plausibility of recovery from common cold as a physical resilience marker needs to be studied further.
This study has some limitations. First, we retrospectively gathered information about recovery from cold; thus, participant recall errors were possible. However, individuals frequently catch the common cold, and self-awareness of days required to recover from a cold is a part of everyday culture. Adults are estimated to experience 2–5 cold events per year; thus, adults aged >25 years will have experienced over 100 episodes of common cold during their lives, making the common cold a familiar part of life.
15) In ideal circumstances, a clinical examination would also have been conducted; however, a more reasonable approach is the use of self-diagnosis in clinical research studies of common cold because of the familiarity of the subjects with common cold and the lack of a biological definition for common cold.
15) Therefore, data on the subjective days required for recovery from a cold are expected to be precise. Second, this study gathered information about colds using a self-report questionnaire; therefore, the answers regarding experiences with common cold might have referred to an illness other than it.
16) However, the self-report format is often used in research because people are generally familiar with colds.
7) Furthermore, the Food and Drug Administration encourages the use of patient-reported surveys that come directly from the patient because they are not biased by interpretations of physicians or others.
17) Third, the perceived time required to recover from common cold may be influenced by subjective health and mood. For instance, respondents with lower EQ-VAS scores recalled more days to recover from the cold, which could be a recall bias. However, the EQ-VAS score was adjusted in these multivariate analyses and the possibility of recall bias was low. We also analyzed its association with the BRS score while considering the EQ-VAS score for subjective health in the ANCOVA. However, the ANCOVA did not include mood or depression, which may have led to recall bias. Fourth, while the BRS has been validated for Korean college students,
10) it has not yet been validated for Korean older adults. Fifth, although we showed an association between days required for recovery from a cold and the psychological resilience scale score, quality of life score, and physical activity level, these relationships may not be enough evidence to represent physical resilience.
Almost all older adults experience common colds; thus, this common stressor may be useful for evaluating physical resilience. Moreover, patient-reported surveys of common colds are reliable. Therefore, our finding of the association between the average number of days required for recovery from common cold and psychological resilience supports its potential as a marker of physical resilience.
In conclusion, the average number of days required for recovery from common cold was strongly associated with psychological resilience. The number of days required to recover from common cold may be an indirect marker for physical resilience, at least with respect to immunity, as it may represent the recovery capacity after a stressor such as a viral infection. Although the recovery days were not related to the frailty index or number of falls in this cross-sectional study, a longitudinal study is needed to measure health outcomes immediately before and after encounter with a stressor.