This study revealed that the prevalence of physical frailty among subjects with heart disease was higher than those without heart disease, consistent with a previous study [9]; the physical frailty of older people with heart disease has a high prevalence (10–60%) and varies according to the instrument used for assessment. In our study, slow gait speed showed a high prevalence in the heart disease group but a significant difference was not found in grip strength. This may suggest that gait speed can be a surrogate marker of physical frailty to detect heart diseases in community-dwelling older populations in order to provide intervention to delay a negative outcome of physical frailty.
Heart diseases and social interaction are associated with physical frailty based on slow gait speed independently of age, sex, and, other risk factors of physical frailty in older populations. Heart disease subjects had a 1.5-times risk of slow gait speed than those without heart disease but this was not associated with the grip strength. Social interaction was independently associated with physical frailty based on the frequency of going outdoors and was negatively associated with all types of physical frailty, and the frequency of direct social contact was negatively associated with gait speed and physical frailty but not associated with grip strength. In heart disease subjects, the results indicate that living alone and direct social contact were independently associated with physical frailty. This finding indicates that heart diseases and social interaction such as going outdoors and direct social contact influence physical frailty in general community-dwelling older populations. For heart disease subjects, living alone and frequent direct social contact were associated with physical frailty, particularly slow gait speed. This result is in line with previous studies on the role of cardiovascular disease associated with physical frailty-related criteria, such as gait speed, grip strength, and fatigue [11,12, 31, 32]. Furthermore, this study has a novel that the associations between heart diseases and physical frailty that we found were interesting because this study also included the oldest old population while previous studies, a few studies specifically enrolling the oldest age people in community-dwelling. To the best of our knowledge, this is the first time found that in older people with heart diseases, some social factors: living alone and frequency of direct social contact significantly associated with physical frailty, especially slow gait speed.
The present findings of social interaction (frequency of going outdoors and frequency of direct social contact) being associated with physical frailty in older populations also support findings of a cross-sectional study involving 1,200 Koreans aged 70–85 whereby the frequency of social contact was strongly associated with frailty [33]. However, this study generated the new finding that the frequency of direct social contact is associated with physical frailty in older people with heart disease.
The potential mechanisms that could explain the association between heart diseases and slow gait speed can be divided into three different pathways. Firstly, heart diseases represent a chronic illness and have an impact on functional decline; as a by-product of the extra energy generated by mitochondria, they produce excessive amounts of free radicals. This is the oxidative stress pathway and it leads to inflammation due to the elevated level of inflammatory cytokines causing many cellular and tissue changes, including the mobilization of amino acids from muscle tissue to other organ systems resulting in muscle loss and sarcopenia, which has also been associated with physical frailty [34, 35]. Secondly, heart diseases are associated with slow gait speed occurrence due to atherosclerosis, as a state of chronic inflammation that is the major cause of heart diseases. Atherosclerosis refers to the accumulation of fatty and fibrous in the arterial wall, the cause of reduced blood flow at myocardial, which is an impact on end-organ reserve, and reduced physiological function, these reasons are leading cause of slow gait speed [31]. Because walking requires multiple organ functions such as heart, lung, brain function, and musculoskeletal muscles work together and require energy more than grip strength. Finally, the mechanism could explain by those with heart disease who had a low physical activity may be the result of symptoms of heart diseases such as fatigue, chest pain, dyspnea, loss of diet appetite, and so on, are leading cause loss of muscle mass and strength called sarcopenia. Sarcopenia is a major component of physical frailty [36]. On the other hand, physical frailty also could be a cause of physical inactivity, which is an important risk factor of heart diseases, a recent longitudinal study with 3,896 older adults in 60-year-old during a median 14 year of follow-up, revealed that frail participants were less physically active than a robust group and adequate physical activity was associated with lower risk of all-cause and CVD mortality in this population [32]. Another study found that sarcopenia was significantly correlated with left ventricular (LV) mass in a community-dwelling older population. Older people with sarcopenia had a lower ventricular mass and lower left atrium (LA) volume than those who without sarcopenia [37] being consistent with the Cardiovascular Health Study indicating that LV mass was associated with coronary heart disease in older participants [38].
These and our results suggest that heart diseases have linked to physical frailty by physical activity and sarcopenia. In part of social interaction, frequency of going outdoors and frequency to contact social directly were associated with physical frailty, could explain the association by those who had more often going outdoors and more often contact social directly can get benefit from increase a physical activity causal to improve muscle strength could prevent physical frailty [39]. Moreover, a recent study suggested that a lower frequency of going outdoors could be a cause of physical and mental frailty [40].
In older patients with heart diseases, social factors such as living alone associated with physical frailty could explain the association by a psychophysiology mechanism with those living alone being more likely to have lower physical activity levels than those living with others [41]. Physical inactivity is a cause of losing muscle mass and strength. Recent studies in the Japanese older population have revealed that older who live alone more likely poor social support and had a decline in dietary variety included difficulty to provide a healthy diet [42] and they had poor appetite more than those who not living alone [43]. Our study found that older people with heart disease had a significantly lower albumin level than those without heart disease (Table 1). These reasons may be the cause of muscle strength weakness due to malnutrition. This is the first study to find that living alone is significantly correlated with physical frailty in older patients with heart disease, but this result is in line with frailty and living alone in older populations which indicated that men living alone have a high risk of frailty [44]. The association between frequency of direct social contact and physical frailty could explain the association by those had more frequency of direct social contact have a more physical activity that will improve muscle strength. This result supports a previous study reporting that social frailty (including social role, social network, and social activity) is an important factor that is a leading cause of physical frailty, especially in those with a slow walking speed in the cohort study [45].
According to the results of the present and previous studies in older populations, heart diseases and social interaction were associations with physical frailty. Older people with heart disease, living alone and direct social contact were significant associations with physical frailty.
The study has important strengths. The study was based on older populations in the community including the oldest populations and used gait speed and grip strength as surrogate markers of physical frailty, which are simple tools and powerful predictors of a negative outcome in community-dwelling older populations. In addition, the covariates that are studied were common variables covering physical factors, biological factors, lifestyle-related factors, and socio-demographic factors.
This study has limitations, this is a cross-sectional study that is difficult to determine the causal direction and there are some variables that were not measured as confounding factors such as physical activity level or psychological factors that cannot be overlooked. Our study data were collected from community-dwelling older populations that have assessed the participants that visited at the community center, therefore the subjects with a moderate or severe symptom of physical frailty may not participate that could make the prevalence of physical frailty was underestimated. There was a small sample size of heart disease group that made we could not examine the association between a specific type of heart disease and physical frailty. The data of heart disease experience were obtained from self-report that could not be avoiding recall bias. The lack of data on cardiac examination such as echocardiography, ECGs, or other tests means that we could not confirm the diagnosis or explain the heart function.