Abstract
Background
With the rapid increase in population longevity, more clinical attention is being paid to the overall health of long-lived people, especially centenarians. Subjective health, which is the perception of one’s health status, predicts both mortality and declining physical function in older adults. The purpose of this study was to investigate the factors related to subjective health among centenarians and near-centenarians (ages ≥95) living in a rural area of South Korea.
Methods
A total of 101 participants were enrolled from four different regions (Gurye, Gokseong, Sunchang, and Damyang), known as the Longevity Belt in Korea. Variables assessing physical and mental health, including the results of blood tests, were examined. Factors associated with good subjective health were identified with logistic regression analysis.
Results
Fifty-six participants (59.6%) were subjectively healthy among the centenarians and near-centenarians. Logistic regression analysis revealed that depressive mood was the only factor associated with subjective health and was negatively correlated. The regression model explained 39% of the variance in subjective health.
Conclusions
These findings emphasize the importance of mental health at very advanced ages. Because depressive mood negatively correlates with subjective health, more attention is needed to prevent and manage mood symptoms of people of advanced ages, including centenarians.
Background
The subjective health issue in gerontology research has special value, because subjective health predicts mortality and declining physical function in older people [Citation1–4]. Interestingly, some research has shown that the best predictor of overall health is an individual’s subjective health perception [Citation5]. In a study of older adults, French et al. [Citation6] reported that when they compared age groups of late middle age (60–64 years), young-old (65–74 years), old-old (75–84 years), and oldest-old (85 years and older), subjective health declined with age. However, approximately two-thirds of oldest-old respondents reported that their health was at least good. This pattern was also found in two other cohort studies [Citation7,Citation8]. However, there is also evidence that subjective health declines until 85 years of age and improves in the late elderly. In the case of centenarians, a Chinese study of centenarians reported that centenarians were more likely than octogenarians or nonagenarians to report their health status positively [Citation9].
Centenarian and near-centenarian populations are growing rapidly and are estimated to number 25 million worldwide by 2100 [Citation10]. Consequently, more clinical attention is being paid to the overall health of these age groups. A systematic review reported that most centenarians are classified as pre-frail and frail with low physical activity, weakness, and slow walking speed [Citation11]. Approximately 50% of centenarians show clear symptoms of cognitive decline in cross-sectional studies [Citation11,Citation12]. In contrast with these physical findings, other studies revealed that 46.5% [Citation13], 73% [Citation14], 67% [Citation15], 66.8% [Citation16], and 54.3% [Citation9], of centenarians are subjectively healthy. Even centenarians with severe dependence and comorbid diseases showed reasonable to excellent subjective health [Citation13]. This discordance emphasizes the importance of subjective health, which is why we have become interested in the subjective health of adults of advanced old age.
To clarify the positive effect of subjective health, it is important to evaluate relevant factors that may influence subjective health. So far, only a few studies have carried out multinomial analysis to detect factors associated with subjectively healthy centenarians and near-centenarians. The Georgia Centenarian Study revealed that diseases, health problems (e.g. chest discomfort, numbness, arthritis), and disabilities [activities of daily living (ADL)] are negatively associated with subjective health, whereas albumin levels are positively associated [Citation17,Citation18]. In another study, Liu and Zhang [Citation9] reported that male gender, older age, living with family, ADL score, and chronic diseases are significantly associated with better subjective health. Tigani et al. [Citation16] investigated relationships between subjective health and sociodemographic and disease-related variables, lifestyle variables, and psychosocial variables, respectively. In that study, living alone, having no disease, having autonomy, being satisfied with sleep, not feeling only, and being highly optimistic were independently associated with good subjective health [Citation16]. However, among the four studies, two studies included all participants aged 60 or more (including centenarians) in their analysis, making the results less applicable to the advanced old age group [Citation9,Citation17]. In addition, no studies have evaluated all aspects of health, including general health, physical and cognitive functioning, mental health, and social functioning. Furthermore, the variance of the model predicting subjective health was relatively low, 17% [Citation18] and 22.4% [Citation16], respectively.
To address these limitations, we investigated the factors related to good subjective health through comprehensive evaluations of centenarians and near-centenarians.
Methods
Study outline and participants
Data were collected from the Korean Gugoksundam Centenarian Study in 2018. The Korean Gugoksundam Centenarian Study aims to investigate the biopsychosocial factors contributing to the longevity of Koreans by collecting data from four regions (Gurye, Gokseong, Sunchang, and Damyang) known as the Longevity Belt in Korea. This study enrolled 101 participants aged ≥95 years who were interviewable and had at least one caregiver in the family who could provide detailed information on the participant. Ninety-four centenarians and near-centenarians were included in the present study; the others were excluded because they could not complete the evaluation for subjective health. This study was approved by the Institutional Review Board (CNUH 2018-151). All participants provided written informed consent before participating.
Sociodemographic characteristics
We collected the following sociodemographic information: age (in years), gender (male, female), literacy [illiterate, semiliterate (i.e. can read but cannot write), and literate], living status (living alone, living with others), and family history of longevity (parents or siblings who lived 85 years or more).
General health and social functioning
Subjective health was assessed by the question, “How do you rate your health status in general?” Among the five possible answers (“very good,” “good,” “fair,” “poor,” and “very poor”), we used two categories to analyze “good” (very good/good) and three categories to analyze “poor” (fair/poor/very poor). The number of illnesses was reported in a yes/no format as to whether the participant had a specific disease in the list. The list included 11 diseases commonly found in older populations: diabetes, hypertension, osteoarthritis, osteoporosis, fracture, cardiovascular disease, cancer, renal disease, liver disease, asthma, and cerebrovascular disease. The total number from the list was used in the analysis. Systolic and diastolic blood pressure measures were obtained once with a brachial cuff, and pulse rate was also measured. Participants were asked about their total sleep time in hours. Chewing difficulty and hearing difficulty were assessed using a single-item question each, and when dentures or hearing aids were usually used, answers were given according to the wearing conditions. Daily physical activity (“30 min or more”/“less than 30 min”) and frequency of social contact (“high”/“low”) were assessed by use of the following questions: “How often do you do physical activities such as walking and cycling a day?” and “Do you often hang out with others?”
Mental health
Depressive symptoms were measured by use of the short version of the Geriatric Depression Scale (GDS), which is a 15-item, well-established scale used to evaluate depressive symptoms in older adults [Citation19]. The total score was calculated by counting the responses that suggest probable depression. Scores ranged from 0 (no depressive symptoms) to 15 (severe depressive symptoms).
Cognitive and physical functioning
Cognitive capacity was examined with the Mini-Mental State Examination (MMSE) [Citation20]. The MMSE is commonly used to evaluate cognitive function in centenarian studies. It is composed of five sections: orientation, registration, attention and calculation, recall, and language. A higher score indicates high cognitive capacity. Physical functioning was examined with the 7-item Korean Activities of Daily Living (K-ADL) and 10-item Korean Instrumental Activities of Daily Living (K-IADL) scales [Citation21]. The K-ADL scale includes items on getting dressed, washing one’s face and hands, bathing, eating meals, leaving a room, using the toilet, and urinating and/or defecating; the K-IADL scale includes items related to personal grooming, going out for short walks, using transportation, making/receiving phone calls, managing money, doing household chores, preparing meals and cooking, shopping, taking medications, and doing laundry. Whether participants are independent, partially dependent, or totally dependent for each item was checked. Items were scored as dependent (partially dependent or totally dependent, “1”) and independent (“0”). The sum of items of the K-ADL and K-IADL was used in the analysis. Hand grip strength was assessed in both hands using a hand dynamometer (GRIP-D TKK 5401, Takei Scientific Instruments, Tokyo, Japan). Analyses used the average peak value across both hands. Gait speed (m/s) was calculated based on the time participants took to walk 5 m at their normal speed.
Laboratory tests
Nonfasting blood samples were collected. Total cholesterol, HDL cholesterol, triglyceride, total protein, albumin, blood urea nitrogen (BUN), creatinine, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin, direct bilirubin, C-reactive protein (CRP), and uric acid were measured.
Statistical analysis
To describe the characteristics of the sample and identify the factors contributing to subjective health in near-centenarians and centenarians, we divided the participants into two groups according to subjective health. Characteristics, functioning, and laboratory test results were compared between the two groups using the independent t-test and chi-squared test, as appropriate. The significance tests were two-tailed with an accepted significance level of 0.05, chosen after consideration of the false discovery rate (FDR) associated with multiple testing. Independent variables that were significantly associated with good subjective health were selected for subsequent multivariable analysis. Finally, the distribution of subjective health according to the items of the GDS scale was compared using the chi-squared test or Fisher’s exact test. All data were analyzed using SPSS for Windows version 26.0. Statistical significance was defined as p < 0.05 (two-tailed).
Results
A total of 94 participants (61 near-centenarians and 33 centenarians) were included in the analysis. lists the sociodemographic and clinical characteristics of the participants, including laboratory data. The mean age of the participants was 97.9 years, and 81.9% were female. A total of 59.8% were illiterate, and 41.5% lived alone. About 60% of the sample reported they were subjectively healthy. The mean value of the number of diagnosed illnesses was 1.1. The mean score of the GDS (2.3) was in the normal range. Mean scores for the MMSE (13.8), hand grip strength (5.2 kg), and gait speed (0.23 m/s) indicated that the participants had reduced cognition and physical health. Most of the participants’ laboratory test results were in the normal range. In the comparison of participant characteristics according to gender, women were shown to be less educated and more compromised cognitively and physically than men (i.e. lower MMSE score, hand grip strength, and gait speed, all p < 0.05). By contrast, women had lower creatinine, AST, and ALT levels than men, indicating better renal and liver function (all p < 0.05).
Table 1. Sociodemographic, general health and social functioning, mental health, cognitive and physical functioning, and laboratory test results of centenarian and near-centenarian participants.
Relationships between the sociodemographic and clinical characteristics of the participants according to their subjective health status (i.e. good vs. poor) are summarized in . Having no hearing difficulty, having a lower GDS score, having a higher MMSE score, having a lower ADL score, and having higher hand grip strength were associated significantly with good subjective health in centenarian and near-centenarian participants (FDR-adjusted p < 0.05).
Table 2. Relationships between clinical characteristics and subjective health of centenarian and near-centenarian participants.
In the multivariable analysis, only a lower score on the GDS (adjusted odds ratio = 0.727, 95% confidence interval = 0.577–0.916) was independently associated with good subjective health in near-centenarians and centenarians (). The model explained 39% of the variance in the participant’s subjective health.
Table 3. Logistic regression models of factors predicting good subjective health in centenarian and near-centenarian participants.
We analyzed all items of the GDS according to subjective health, as shown in . Seven of 15 items were found to be associated with subjective health. Of those seven items, four were related to dysphoric mood, i.e. “Basically satisfied with life (reverse-scored),” “Often get bored,” “Happy most of the time (reverse-scored),” and “Wonderful to be alive (reverse-scored)” and three were withdrawal-apathy-vigor items, i.e. “Dropped activities and interest,” “Prefer to stay home,” and “Full of energy (reverse-scored).”
Table 4. Geriatric Depression Scale (GDS) single-item comparisons according to subjective health.
Discussion
The present study identified that depressive mood is negatively associated with one’s perception of health among Korean centenarians and near-centenarians. The result is reliable as it was derived through comprehensive evaluation including physical, functional, cognitive, and psychosocial factors. In addition, the regression model explained 39% of the variance in subjective health.
The participants in this study were born between 1911 and 1923 and lived in a rural area. The historical background of Korea at the time they were raised was nutritionally, hygienically, and educationally deprived due to war and poverty. Therefore, compared to the other centenarian studies, our participants showed lower MMSE scores, hand grip strength, and gait speed, indicating reduced cognitive and physical status [Citation15,Citation22,Citation23]. Interestingly, the participants were frail but had few chronic diseases. We assume that most of our participants lived without clinically demonstrable diseases, placing them in the “escapers” morbidity profile as defined by Evert et al. [Citation24]. More than 76% of participants were not clinically depressive, and over 60% reported feeling subjectively healthy. To sum up, centenarians and near-centenarians who participated in this study had few diseases and were relatively in a good mood. They were functionally and cognitively compromised, but most of them felt their health was good, very good, or excellent.
Previously, relatively good mental health of centenarians was reported, implying considerable resilience in the very old [Citation15,Citation25–29]. Our results appear consistent with the prior research. The mean GDS score of the total participants in our study was 2.3, which is in the normal range. One reason for this finding may be the sociocultural background of Korea, which regards longevity as a very special blessing. In addition, as seen in , most centenarians (over 90%) gave a positive answer to several items, which may also have contributed to the low total GDS score. Those items are questions comparing oneself to others (“Most people are better off”) and questions related to hopelessness (“Feel life is empty”). In Korea, centenarians are a group recognized as achieving great success in terms of longevity. Thus, they may feel better than others and may not have any further desires for the future.
The average GDS score of the participants was low, but GDS scores were divergent between the group with good subjective health and those without. Multivariate analysis revealed that low depressive mood was solely associated with good subjective health. Other factors that were related to subjective health (functional capacity, physical status, and literacy) did not show any significance in the multivariate analysis. This is inconsistent with previous results suggesting that objective health is independently related to subjective health [Citation9,Citation16–18]. However, there are other studies in which the association between subjective health and objective health decreased, and in which the association between subjective and mental health increased with age [Citation30]. Lau et al. also found that depressive mood aggravated poor health perceptions among frail centenarians [Citation31]. In line with previous study, our results reinforce the importance of mental health for subjective health at very advanced ages. This might be explained by the fact that depressive mood interferes with centenarians accepting their inevitable functional loss and decreased activity [Citation32]. Depression may disrupt the disregard of physical limitations in the evaluation of health, especially in those who are prone to physical frailty [Citation31]. Moreover, depressed individuals may be more pessimistic and perceive less control over their health problems, resulting in poor subjective health [Citation33,Citation34].
Although the association was not significant in the multivariate analysis, cognition was related to subjective health in the univariate analysis. Individuals with higher cognitive ability may better recognize the positive aspects of life and adapt to the aging process, which can improve life satisfaction—and may affect the perception of one’s health [Citation35]. In other centenarian studies, having an illness was a common factor influencing subjective health, but our present study revealed the contrary finding that despite illness, mood took priority in determining subjective health. This is probably due to the small number of participants with underlying diseases. However, the number of centenarians with chronic diseases will increase as health care advances. Then, managing illness might be an important factor in one’s subjective health in the near future.
In our study, many participants expressed a favorable self-assessment of their subjective health status. Chinese centenarian study also revealed a more positive self-rated health evaluation among centenarians than octogenarians [Citation9]. However, studies targeting other elderly populations indicate a decline in subjective health with age [Citation6,Citation36]. This signifies the distinctive nature of centenarians compared to other age groups. Furthermore, while various factors are associated with subjective health in other elderly populations [Citation3,Citation37], our study revealed a significant relationship only with depressive mood, thereby emphasizing the importance of mental health in the extremely advanced age group.
This study has several limitations. Firstly, recruitment was performed in a rural area, which may limit the study’s generalizability but adds strength in terms of consistency in evaluating participants. Findings were also drawn exclusively from a Korean population, and replication is required in other ethnic groups. Secondly, a bidirectional relationship needs to be considered in relation to subjective health and depression, as this study was designed to be cross-sectional. Thirdly, we did not assess potential factors that could impact both subjective health and depression, such as personality traits. Fourthly, centenarians with very poor cognition were not included in this study because we enrolled participants who could be interviewed. Accordingly, the depressive mood of the study sample might not represent the mood status of the whole centenarian population. Finally, the predominance of female participants makes the characteristics of male centenarians less prominent. However, the high representation of females is common in very advanced age groups and is considered indicative of centenarian attributes. Future research focusing on centenarian men is needed to provide a more comprehensive understanding of this age group.
The study, however, also has several strengths. Firstly, to our knowledge, this is the first study to investigate factors of subjective health among a large sample of centenarians and near-centenarians through thorough evaluations. Secondly, since the study participants were recruited from four different longevity areas, the bias of single-site recruitment could be excluded. Finally, the goodness of fit of a regression model in the subjective health was 0.39, which is rather low but the highest among other studies with the same design.
Conclusion
In conclusion, low depressive mood is associated with better subjective health among centenarians and near-centenarians. Comprehensive evaluations, including physical, functional, cognitive, and psychosocial factors, render the findings more likely to be robust. To improve subjective health that predicts mortality, clinical attention is needed to the mental health of people of advanced ages. Future longitudinal research is needed to clarify the causal relationship and factors potentially mediating the association between subjective health and depression. Moreover, these results foretell an urgency to design effective preventative interventions for better quality of life in the advanced aged group given that centenarians are rapidly increasing in number.
Author contributions
Access to data and data analysis: MJ, MHS, and KP had full access to all the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: KP and SCP. Acquisition of data: All authors. Interpretation of data: MJ and KP. Drafting of the manuscript: MJ was responsible for writing the original draft of the manuscript; KP and SCP supervised it. Critical revision of the manuscript for important intellectual content: All authors.
Ethics approval and patient consent statements
This study was approved by the Ethics Committee of Chonnam National University Hospital Institutional Review Board (CNUH 2018-151). Written informed consents were provided by all participants. The study was conducted according to the ethical principles for medical research involving human subjects detailed in the Declaration of Helsinki.
Consent for publication
Not applicable.
| Abbreviations | ||
| GDS | = | Geriatric Depression Scale |
| K-ADL | = | Korean Activities of Daily Living |
| K-IADL | = | Korean Instrumental Activities of Daily Living |
| MMSE | = | Mini-Mental State Examination |
| BUN | = | Blood urea nitrogen |
| AST | = | Aspartate aminotransferase |
| ALT | = | Alanine aminotransferase |
| CRP | = | C-reactive protein |
| FDR | = | False discovery rate |
Acknowledgments
The authors would like to thank all participants in this study.
Disclosure statement
The authors declare that there are no potential conflicts of interest relevant to the publication of these results.
Data availability statement
The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Additional information
Funding
References
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