Frailty is described as a loss of the ability to cope with external stressors due to diminished functional reserves and is closely related to clinical adverse outcomes including increased dependence, hospital admission, and mortality, thereby causing increased requirements for social resources that serve the aging population [1-3]. Frailty is measured with the Fried operationalized frailty with a phenotype model, which includes involuntary weight loss, exhaustion, slow gait, poor handgrip strength, and sedentary behavior [2]. The Rockwood and Mitnitski group defined frailty using the Frailty Index, which measures cumulative deficits in the areas of physical, cognitive, psychological, and social health. Many chronic diseases are included in the Frailty Index [4].

Although frailty is understood to be promoted by physiological and biochemical changes due to aging together with malnutrition and a lack of physical activity, research has shown that frailty is highly associated with chronic diseases including hypertension, congestive heart failure (CHF), diabetes mellitus (DM), stroke, chronic lung disease, and cancer [5-8].

As a simple screening method for frailty, Morley et al. [9] proposed the Fatigue, Resistance, Ambulation, Illness, and Loss of Weight (FRAIL) questionnaire, with frailty being positive when five out of 11 designated illnesses are present (i.e., hypertension, DM, cancer [other than minor skin cancers], chronic lung disease, heart attack, CHF, angina, asthma, arthritis, stroke, and kidney disease). However, only 2.1% to 2.9% of community-dwelling older adults had five or more illnesses in previous studies per this questionnaire [10]. Also, asthma and chronic obstructive pulmonary disease (COPD) cannot be easily distinguished by laypersons. Indeed, studies showed that community-dwelling older adults in Korea are less aware of their illness status [11,12]. These observations suggest that the “illness items” used to identify high-risk frailty groups or to screen for frailty in community-dwelling older adults must be different.

Therefore, the aim of this study was to identify current illnesses related to frailty in community-dwelling older adults.

The results of this study revealed that current hypertension, DM, chronic lung disease (i.e., COPD, chronic bronchitis, emphysema, and asthma), arthritis, urinary incontinence, and osteoporosis were significantly related to frailty in Korean community-dwelling older adults.

Several studies have assessed the association of frailty with hypertension. Frailty is common in people with hypertension, as both conditions are associated with an unhealthy lifestyle including high BMI, large waist circumference, high smoking rate, and low physical activity rate [26-28]. In addition, cardiovascular diseases (CVDs) associated with hypertension can accelerate frailty, and frailty increases the risk of adverse outcomes in patients with CVD. This may be because frailty and CVD share pathobiology, particularly inflammatory biomarkers such as interleukin-6 and C-reactive protein. These factors, like immune cells and cytokines, promote atherosclerosis and damage arterial walls, affecting cellular aging and promoting frailty [29]. Through this process, frailty may manifest as clinical heart disease in response to stressors such as coronary ischemia or pressure or volume overload [30], suggesting relevance of frailty in terms of development, manifestation, and progression of heart failure. Several studies indicate that patients with CHF who were frail had high risks of mortality, hospitalization, and impaired quality of life [31-33]. In older patients with acute coronary syndromes, frailty is associated with a significant increase in mortality [34,35].

DM may increase the risk of both CVD and frailty [36]. DM often causes functional impairments in muscles and nerves, thus leading to a deterioration in physical function. Insulin resistance or insulin depletion may be an important factor in the development of frailty in diabetes patients, since insulin is well-known as an anabolic hormone in muscle [37].

Frailty is an independent risk factor for the development of COPD, and COPD can lead to frailty [38]. Frailty is increased in the presence of chronic respiratory disease overall, ranging from 5% to 65%. This variation is likely due to differences in the criteria used or settings studied. Physical inactivity due to breathlessness and increasing comorbidity burden in chronic respiratory disease patients increase the prevalence of frailty [39].

Chronic kidney disease (CKD) is known to be associated with frailty [5-8]. The inflammatory state related to CKD not only causes skeletal muscle resistance to insulin but is also associated with an increase in resting energy expenditure that may contribute to an imbalance in muscle protein homeostasis and, in turn, frailty syndrome [40,41].

Similarly, stroke is known to be related to frailty. Previous studies have shown that markers of physical function were consistently associated with survival and recovery after ischemic stroke. Inflammation, kidney function, and frailty also seemed to be determinants of survival and recovery after an ischemic stroke [42].

In accordance with previously reported associations between arthritis, osteoporosis and disability, we found relationship between these skeletal problems and frailty spectrum in this study [30-32]. Similarly, functional limitation and disability are strongly associated with frailty, which affects 4% to 17% of older adults in the community [2,43].

We found that urinary incontinence is correlated with frailty. According to the results of previous studies, the frailty factors related to urinary incontinence were falls, poor grip strength, unintentional weight loss, and slow walking speed. Slow walking may contribute to diminished mobility and lower body strength that leads to pelvic floor muscle discoordination and urinary incontinence [44,45]. In addition, the presence of frailty indicates a diminished physiological homeostatic capacity that is strictly correlated with a diminished capacity to use energy and leads not only to sarcopenia and cognitive decline but also increased mortality [46-49].

In the Cardiovascular Health Study, only 9.7% of older adults with multiple morbidities were frail, while 67.7% of frail older adults had multiple morbidities [2]. Non-frail older adults had an average of 1.4 chronic diseases, whereas frail older adults had an average of 2.1 chronic diseases [50]. Therefore, identifying comorbid diseases might be a clinically relevant issue in approaching older adults with frailty.

However, community-dwelling older adults often have low awareness of their illnesses. In this study, participants indicated that their prevalence rates of COPD (1.1%), CHF (0.7%), and MI (2.2%) were lower than in previous studies [2,5,8,51]. These findings may be due to the participation of relatively healthy ambulatory people in the study or could have resulted from a low perception of these diseases in Korean older adults. Lee et al. [12] reported that the awareness of cardio-cerebrovascular disease was only 8.9% among the Korean population older than 70 years of age. The prevalence of COPD is reported to be approximately 11% to 17% in Korea, and only 1.7% of the national population is reported to receive treatments for COPD [52-54]. In the Chronic Disease Fact Book published in 2017, awareness and treatment rates for chronic diseases (especially DM, hypertension, dyslipidemia, asthma, and COPD) were very low in Koreans [55]. In addition, asthma and COPD frequently overlap, and angina, MI, and heart failure are not always easily differentiated [56].

Indeed, the results of the study showed a large gap between the level of awareness of illness and objective clinical data. For example, 453 (15.4%) patients in the study had an estimated glomerular filtration rate of less than 60 mL/min/1.73 m² according to the Modified Diet of Renal Disease equation, but only 46 participants (1.6%) answered that they had kidney disease. Also, while 76 participants (2.6%) reported they were diagnosed with depression, 651 participants (22.2%) were suspected to be depressive according to the short-form Geriatric Depression Scale using a cutoff value of six points or higher.

Chun et al. [57] demonstrated that a lack of access to information, knowledge, or health care services can lead to a lack of awareness or treatment of disease, and this may be more likely to occur in older people or in rural area residents. In addition, socioeconomic status is closely related to a lower rate of health information acquisition and may affect the perception accuracy of chronic diseases [58,59].

This study has limitations in that we could not confirm the accuracy of disease history. This may lead to a difference between actual disease findings and the results of the interviewed self-report. However, in one study conducted in Japan, there was a high degree of agreement with the actual medical history of chronic diseases [60]. The average number of comorbidities was 2.4 in this community study as confirmed by the questionnaire, and the prevalence rates of hypertension and DM were 58.0% and 22.2%, respectively among the elderly in the community, also confirmed by the questionnaire. The average is not so different from the results of the ‘Living profiles of older people surveys in Korea’ reported in 2014, in which the older adults had an average of 2.6 chronic diseases and prevalence rates of hypertension and DM of 56.7% and 22.6%, respectively [17]. However, self-reported disease prevalence can be underestimated compared with actual disease prevalence. COPD is a representative example. Also, MI or stroke within six months, uncontrolled hypertension, and cancer under treatment were excluded from this study and, therefore, the results of CVD prevalence and cancer can be lower than those in the actual conditions.

Unlike many studies, heart and lung disease, and cancer were not significantly related to frailty in this study. The reason for this may be that we excluded those who had experienced a cerebrovascular accident or MI within the past six months or who had an active malignancy currently under therapeutic treatment, and this may explain why heart disease and cancer were not associated with frailty in this study. It may also result from the cross-sectional study design. In particular, many chronic diseases such as CHF, MI, and angina may cause different results in longitudinal studies because they cause functional declines and accelerate frailty. However, the purpose of this study was to investigate illnesses associated with frailty and, based on the results, we can reasonably suspect the presence of frailty in older adults with theses illnesses. Further follow-up studies on the effects of diseases on frailty will be needed in the near future.

Nevertheless, the strength of this study is that the sample size was comparatively large (2,936 participants) and the participants represent typical community-dwelling people aged 70 to 84 years in Korea.

In conclusion, hypertension, DM, chronic lung disease (COPD, chronic bronchitis, emphysema, and asthma), arthritis, urinary incontinence, and osteoporosis were significantly related to frailty in Korean community-dwelling older adults. In particular, DM, and urinary incontinence were significantly associated with frailty even after adjusting for various factors.