The Mediating Effect of Chronic Pain on the Relationship between Falls and Frailty: A Cross-sectional Survey among Middle-aged and Older adults from Ethnic Minority Groups in Yunnan Province, China

doi:10.21203/rs.3.rs-3336089/v1

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Research Article

The Mediating Effect of Chronic Pain on the Relationship between Falls and Frailty: A Cross-sectional Survey among Middle-aged and Older adults from Ethnic Minority Groups in Yunnan Province, China

https://doi.org/10.21203/rs.3.rs-3336089/v1

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Background

Falls are associated with an increased risk of frailty in middle-aged and older adults; however, the mediating role between falls and frailty remains unclear. The primary objective of this study is to examine the relationship between falls and frailty in middle-aged and elderly individuals residing in Yunnan Province, China, with a specific emphasis on exploring the potential mediating effect of chronic pain across different ethnic groups.

Methods

Employing a cross-sectional design, data collection was conducted from July to December 2022 in five selected counties. Baron and Kenny’s causal steps method was used to explore the mediating effect of chronic pain on the relationship between falls and frailty. Spearman correlation analysis, multiple linear regression models, and bootstrap method were employed for data analysis.

Results

A total of 2,710 respondents participated in this study. The prevalence of falls among middle-aged and older individuals was 12.77%, while the prevalence of frailty in the same population was observed to be 21.62%. Spearman correlation analysis revealed significant positive association between chronic pain and both falls (r=0.135, P<0.05) as well as frailty (r=0.383, P<0.05). Frailty also exhibited a significant positive correlation with falls (r=0.162, P<0.05). After adjusting for all covariates, the total effect of falls on frailty was estimated to be 1.065 (95% bootstrap CI: 0.804~1.326), with a direct effect estimate of 0.797 (95% bootstrap CI: 0.511~1.083). The indirect effect of chronic pain on this association was found to be approximately one-quarter at 0.268 (95% bootstrap CI: 0.170~0.366). The subgroup analysis discovered differences in the mediating effects across different ethnic groups; specifically, the proportions mediated by chronic pain were found to be 28.2%, 18.4%, and 21.5% for Han majority group, Zhiguo ethnic minorities, and other ethnic minority groups, respectively.

Conclusion

This study provides valuable insights into the intricate association between frailty, falls, and chronic pain among middle-aged and older adults from diverse ethnic backgrounds in a western province of China. Effective management strategies targeting chronic pain and falls prevention could serve as crucial interventions to address frailty.

Frailty

Chronic pain

Falls

Mediation effect

Ethnic minorities

Middle-aged and older adults

Falls, one of the most common unintentional injuries, have been widely recognized a predominant challenge in geriatric nursing[1]. According to the Global Burden of Disease Study, the incidence, mortality, and disability-adjusted-life-years of falls in the Chinese population increased in rank from 27th in 1990 to 17th in 2017[2]. Statistics show that in 2019, falls contributed significantly to the burden of disease and ranked as the second leading cause of injury-related death in China[3]. In addition to the immediate threat to life, falling also leads to various other health issues. Older adults who experience falls often face long-lasting physical and psychological consequences, with frailty being among the most common[4, 5]. A cohort study indicating that seniors who experience falls are 1.92 times more likely to develop frailty[6]. Particularly noteworthy are the fall-induced consequences such as fractures, infections, and muscle injuries, which have independently been recognized as predictors of both the onset and progression of frailty[7, 8]. This correspondence between falls and an increased likelihood of frailty in older adults has been further substantiated through comprehensive meta-analyses[9, 10].

Chronic pain, presenting as a common outcome of falls[11], endures for extended durations, often spanning months or even years, thereby exerting a deleterious impact on an individual's quality of life and impeding their ability for movement[12], emotion management[13] and social contact[14, 15]. Cohort studies have shown that obvious injuries and fractures sustained by older adults after a fall, or even soft tissue injuries, sprains, muscle strains, all can contribute to the development of chronic pain[16]. Moreover, community-dwelling elderly people who have experienced falls are particularly susceptible to the development of persistent chronic pain, with a considerable proportion of this group reporting severe discomfort[17]. Chronic pain makes older adults more vulnerable to an increased risk of depression and social isolation, which further leads to the exacerbation of frailty[18, 19].

Extensive research has been conducted to investigate on the mediating function of chronic pain, with a primary focus on physical impairment[20], sleep quality[21], chronic diseases, and depression[22, 23]. Concurrently, certain investigators have also explored the potential mediating influences of social participation[24], activity engagement[25] as mediating variables for falls and frailty. However, the relationship among falls, chronic pain, and frailty has not been extensively studied, especially among middle-aged and older adults in ethnic minority regions.

Yunnan Province accommodates 26 of China's 55 ethnic minorities[26], with their settlements primarily situated in economically underdeveloped rural regions characterized by inadequate infrastructure, low productivity, and limited availability of resources[27]. Despite significant advancements during China's overall progress, these circumstances pose substantial challenges for improving the health of ethnic minorities. In recent years, as the aging population continues to grow, ensuring the health security of elderly individuals from different ethnic groups has become an integral part of China's pursuit towards achieving universal health coverage. This pressing need necessitates relevant research to investigate the factors influencing the health status of older people across diverse ethnicities.

The primary purpose of this study is to examine the correlation between falls and frailty in middle-aged and elderly people in Yunnan Province, China, with a particular focus on the potential mediating effect of chronic pain. To comprehensively understand the intricacies across various ethnicities, the study is designed with three main objectives: (1) to assess the association between chronic pain, falls and frailty among middle-aged and older adults in ethnic minority regions, (2) to investigate the mediating role of chronic pain on the relationship between falls and frailty, and (3) to explore potential disparities in the mediating effects among distinct ethnic groups, ultimately offering novel insights for elderly care strategies tailored to this vulnerable population.

Study design

A cross-sectional design was employed to collect data from July to December 2022 in Yunnan Province, China. The selection of study sites was based on geographical characteristics, economic development status, and the distribution of ethnic minority populations. Consequently, five counties representing diverse ethnic minority settlements and varying levels of economic development were chosen from the eastern, central and western regions of the province. Within each selected county, one township and two villages were randomly selected for respondents recruitment. The inclusion criteria for participants included individuals aged 45 years or older as of 2022 with a residency duration of at least three consecutive months in the local area and without significant intellectual or mental disorders. The recruitment of all potential participants from each village was conducted using cluster sampling. Participants were given the choice to either independently complete the survey or receive assistance from an interviewer. All participants were volunteers who had provided informed consent prior to face-to-face interviews using a structured questionnaire. Our interviewers, who possessed expertise in population-based surveys, underwent standardized training specifically tailored for this study.

A total of 2,730 individuals were invited to participate in the survey. However, upon careful examination of the collected data, 15 participants were excluded due to missing key variables and 5 participants were excluded as their age was below 45 years. As a result, the final sample size for analysis consisted of 2,710 participants, including 814 Han majority (30.04%), 1,036 Zhiguo ethnic groups (38.23%), and 860 other ethnic minorities (31.73%). Our study protocol underwent review and approval by the Ethics Review Committee of Kunming Medical University.

Measurements

Falls

Falls were operationally defined as unexpected incidents resulting in participants coming to rest on the ground, floor, or a lower level[28]. In our study, participants were asked the following question, "Have you experienced any falls within the preceding 12 months?" The response options provided were binary (Yes or No).

Frailty

The Tilburg Frailty Indicator (TFI), a standardized self-reported questionnaire with 15-item across three domains [29, 30], was utilized to assess frailty. The physical domain consists of eight items encompassing aspects such as physical health, unexplained weight loss, difficulty in walking, balance, hearing problems, vision problems, and weak strength in hand, and physical tiredness. Each item is scored on a scale ranging from 0 to 8 points. The psychological domain includes four items assessing cognition, depressive symptoms, anxiety levels and coping mechanisms. These items are also scored on a scale ranging from 0 to 4 points. Lastly, the social domain includes three items evaluating living arrangements, social relationships and social support with scores ranging from 0 to 3 points. The total TFI score ranges from 0 to 15. An individual with a score of ≥5 is considered frailty: higher scores indicate greater degrees of frailty. Previous studies have demonstrated the reliability and validity of the TFI among the Chinese population[31]. In this study, The Cronbach's alpha coefficient for the TFI was 0.735.

Chronic pain

Chronic pain was defined as persistent or recurrent bodily discomfort lasting for more than 3 months[32, 33]. In our survey, respondents were asked to indicate whether they frequently experienced discomfort due to pain over the past three months with binary options (Yes or No). To further evaluate the intensity of participants’ pain, we utilized a numerical rating scale (NRS) consisting of 10 points. Participants were instructed to select a score ranging from 0 to 10 to describe the severity of their pain[34]. The assigned values for pain points were interpreted as follows: 0 denoted no pain, while scores between 1 and 3 represented mild pain, scores between 4 and 6 indicated moderate pain, and scores between 7 and 10 signified severe pain[35, 36].

Covariates

The covariates consist of two aspects: demographic characteristics and health-related factors. Demographic characteristics encompass ethnicity, age (45-59, 60-69, and ≥70), sex, marital status (whether there is a partner), education level (illiterate, uncompleted primary school, completed primary school, middle school or above), occupation (farmers, non-farm workers), and monthly household income (<1000 RMB, 1000-2999 RMB, 3000-4999 RMB, ≥5000 RMB). To assess the disparities among ethnic minority groups, we categorized them into three groups: Han majority population, Zhiguo ethnic minorities, and other ethnic minorities. The Zhiguo ethnic minorities, also known as "ethnic minority groups directly entering-socialism", refer to those ethnic groups that existed in a primitive or slave society prior to the establishment of the People's Republic of China and transitioned directly into a socialist society without undergoing democratic reforms. Most Zhiguo ethnic minorities inhabit in Yunnan Province. Among the 11 officially recognized Zhiguo ethnic minorities, we have selected six as representatives for this study: Jino, Nu, Bulang, Lisu, Lahu and Wa. Other ethnic minorities included in this study consist of Dai, Bai, Zhuang, Miao, Hui, Yi, Hani, and Yao.

Covariates regarding health-related factors at the individual level included chronic diseases, smoking behavior, drinking habit, and activities of daily living (ADL) as they have been previously associated with frailty in older adults [4, 37, 38]. Respondents were asked to report if they had any of the following chronic conditions: diabetes mellitus, hypertension, dyslipidemia, heart disease, cerebrovascular disease, chronic gastritis, chronic lung disease, chronic nephritis, rheumatoid arthritis, intervertebral disc disease, osteoporosis, ventilation disorder, hyperthyroidism, hypothyroidism, cancer, leukemia, chronic anemia, or other chronic diseases. Chronic diseases were defined as having at least one chronic disease (Yes or No). Smoking status was determined by whether respondents currently smoked or had ever smoked (Yes or No). Alcohol consumption within the past week was also assessed (Yes or No). The Activity of Daily Living Scale[39] was employed to evaluate the ADL status encompassing two components: Physical Activities of Daily Living (PADL) and Instrumental Activities of Daily Living (IADL). PADL consists of six behavioral abilities, namely toileting, feeding, dressing, grooming, walking, and bathing; whereas IADL encompasses eight behavioral abilities including phone usage, shopping skills, meal preparation, housework competence, laundry management capability, transportation aptitude as well as medication and financial management. The total score ranges from 14 to 56 with higher scores indicating greater impairment in daily living functionality for the participant. A score of 14 indicates absence of disabilities while a range of 15-21 represents mild disabilities and a score above or equal to 22 signifies severe disabilities [40].

Statistical analyses

The demographic characteristics and health-related factors of the respondents were described using frequencies (percentages). Chi-square tests were used to compare differences between groups. Spearman correlation analysis was conducted to determine the correlation between chronic pain, falls and frailty were correlated. Baron and Kenny’s causal steps method was used to explore the mediating effect of chronic pain on the relationship between falls and frailty[41]. Following the proposed procedures of this method, a three-step estimation approach was applied to analyze the mediating variable. The mediation effect analysis needs to meet the following conditions: (1) falls was significantly associated with frailty (Total effect; Path c); (2) falls was significantly associated with chronic pain (Path a); (3) controlling for falls, chronic pain was significantly associated with frailty (Path b); (4) the relationship between falls and frailty was reduced (Direct effect, Path c’) when controlling for chronic pain (Indirect effect, a×b). Full mediation occurs when inclusion of the mediation variable reduces the observed relationship between independent variable and dependent variable to zero. Partial mediation occurs when inclusion of mediation effect weakens the observed relationship between independent and dependent variable. Recent studies have shown that bootstrap confidence interval is one of the most reliable tests for conducting a mediation analysis[42, 43]. We set bootstrap confidence interval (CI) at 95% with 5,000 bootstrap samples. If zero is not included in 95% CI, it indicates a significant mediating effect[44]. Liner regression models were used for multivariable regression analyses involving continuous outcomes such as chronic pain score and frailty score. All analyses were performed using Stata v.15 software with statistical significance considered at p-value < 0.05.

Demographic and health characteristics among middle-aged and elderly people

A total of 2,710 respondents participated in this study. The prevalence of falls among middle-aged and older individuals was 12.77%, while the prevalence of frailty in the same population was observed to be 21.62%. According to table 1, it is evident that that mild pain was experienced by 30.55% of respondents, moderate pain was reported by 24.91% a smaller proportion (1.88%) reported severe pain. Notably, statistically significant differences (P<0.05) were observed among ethnic groups with respect to age, education, occupation, monthly household income, prevalence of chronic diseases, drinking habits, and ADL. Furthermore, there were also ethnic-based disparities (P<0.05) noted in terms of the incidence of falls as well as the prevalence of chronic pain and frailty.

Table 1 Demographic characteristics and health status of middle-aged and elderly adults by ethnic groups [n (%)]

Variable	Total (n=2,710)	Ethnic groups			χ²	P
Variable	Total (n=2,710)	*Han* majority (n=814)	*Zhiguo* minorities (n=1,036)	Other minorities (n=860)	χ²	P
Demographics
Age
45-59	1,161(42.84)	298(36.61)	513(49.52)	350(40.70)	87.385	<0.001
60-69	863(31.85)	224(27.52)	342(33.01)	297(34.53)
≥70	686(25.31)	292(35.87)	181(17.47)	213(24.77)
Sex
Male	1,218(44.94)	353(43.37)	482(46.53)	383(44.53)	1.924	0.382
Female	1,492(55.06)	461(56.63)	554(53.47)	477(55.47)	1.924	0.382
Marital status
Married	2,054(75.79)	630(77.40)	769(74.23)	655(76.16)	2.587	0.274
Single	656(24.21)	184(22.60)	267(25.77)	205(23.84)	2.587	0.274
Education level
Illiterate (Never received an education)	1,098(40.52)	253(31.08)	459(44.30)	386(44.88)	71.904	<0.001
Uncompleted primary school	586(21.62)	176(21.62)	197(19.02)	213(24.77)
Completed primary school	468(17.27)	159(19.54)	174(16.80)	135(15.70)
Middle school or above	558(20.59)	226(27.76)	206(19.88)	126(14.65)
Occupation
Farmers	1,902(70.18)	398(48.89)	833(80.41)	671(78.02)	253.291	<0.001
Non-farm workers	808(29.82)	416(51.11)	203(19.59)	189(21.98)	253.291	<0.001
Monthly household income (Chinese yuan/RMB)
<1000	623(22.99)	165(20.27)	313(30.21)	145(16.86)	80.704	<0.001
1000-2999	848(31.29)	231(28.38)	338(32.63)	279(32.44)
3000-4999	722(26.64)	235(28.87)	207(19.98)	280(32.56)
≥5000	517(19.08)	183(22.48)	178(17.18)	156(18.14)
Health-related factors
Chronic diseases
Yes	1,572(58.01)	538(66.09)	594(57.34)	440(51.16)	38.581	<0.001
No	1,138(41.99)	276(33.91)	442(42.66)	420(48.84)	38.581	<0.001
Smoking
Yes	906(33.43)	262(32.19)	351(33.88)	293(34.07)	0.818	0.664
No	1,804(66.57)	552(67.81)	685(66.12)	567(65.93)	0.818	0.664
Drinking
Yes	711(26.24)	160(19.66)	313(30.21)	238(27.67)	27.595	<0.001
No	1,999(73.76)	654(80.34)	723(69.79)	622(72.33)	27.595	<0.001
ADL
No disability (Score 14)	1,611(59.45)	525(64.50)	579(55.89)	507(58.95)	15.963	<0.001
Mild disability (Score 15-21)	976(36.01)	253(31.08)	403(38.90)	320(37.21)
Severe disability (Score ≥22)	123(4.54)	36(4.42)	54(5.21)	33(3.84)
Falls
Yes	346(12.77)	127(15.60)	132(12.74)	87(10.12)	11.300	0.004
No	2,364(87.23)	687(84.40)	904(87.26)	773(89.88)	11.300	0.004
Chronic pain
No pain (Score 0)	1,156(42.66)	336(41.28)	392(37.84)	428(49.77)	46.988	<0.001
Mild pain (Score 1-3)	828(30.55)	239(29.36)	344(33.20)	245(28.49)
Moderate pain (Score 4-6)	675(24.91)	222(27.27)	268(25.87)	185(21.51)
Severe pain (Score 7-10)	51(1.88)	17(2.09)	32(3.09)	2(0.23)
Frailty
Yes	586(21.62)	191(23.46)	272(26.25)	123(14.30)	41.938	<0.001
No	2,124(78.38)	623(76.54)	764(73.75)	737(85.70)	41.938	<0.001

Correlation of chronic pain, falls and frailty

The Spearman correlations (r) between three variables, namely chronic pain, falls, and frailty are presented in table 2. For the entire population, a statistically significant positive correlation was observed between chronic pain and falls (r=0.135, p<0.05). Similarly, a significant positive correlation was found between chronic pain and frailty (r=0.383, p<0.05). Additionally, there was a significant positive correlation of 0.162 (p<0.05) between falls and frailty as well. In different ethnic groups, significant positive correlations were also observed among chronic pain, falls, and frailty.

Table 2 Correlations between chronic pain, falls and frailty ( r )

Variables	Whole sample	Han majority	Zhiguo minorities	Other minorities
Chronic pain - Falls	0.135^*	0.185^*	0.088^*	0.133^*
Chronic pain - Frailty	0.383^*	0.369^*	0.403^*	0.339^*
Falls - Frailty	0.162^*	0.197^*	0.138^*	0.142^*

Note: ^* P<0.05.

Mediating effect of chronic pain on the relationship between falls and frailty

The regression model results based on Baron and Kenny's causal steps method were presented in table 3 and Figure 1. After adjusting for all the covariates, the association between falls and chronic pain as found to be significant (β=0.689, 95%CI: 0.458~0.919) for path a. Similarly, controlling for falls, chronic pain showed a significant association with frailty (β=0.389, 95%CI: 0.349~0.429) for path b. Additionally, falls exhibited a significant association with frailty (β=1.065, 95%CI: 0.804~1.326) for path c. After introducing chronic pain into the model as a mediator (path c’), the β coefficient of falls on frailty decreased (β=0.797, 95% CI: 0.551~1.043), suggesting a potential mediating effect of chronic pain on the relationship between falls and frailty. Furthermore, this mediating effect was confirmed across different ethnic groups.

Table 3 Analysis of mediating effect of chronic pain

		Pathway	Whole sample (N=2710)	Han majority (N=814)	Zhiguo minorities (N=1036)	Other minorities (N=860)
		Pathway	β (95% CI)	β (95% CI)	β (95% CI)	β (95% CI)
Fall	Frailty	c	1.065^*(0.804~1.326)	1.185^*(0.737~1.633)	1.036^*(0.595~1.477)	0.791^*(0.336~1.246)
Fall	Chronic pain	a	0.689^*(0.458~0.919)	0.959^*(0.563~1.355)	0.437^*(0.043~0.831)	0.551^*(0.147~0.955)
Fall	Frailty	c’	0.797^*(0.551~1.043)	0.850^*(0.418~1.282)	0.846^*(0.438~1.253)	0.621^*(0.181~1.061)
Chronic pain	Frailty	b	0.389^*(0.349~0.429)	0.349^*(0.274~0.424)	0.435^*(0.372~0.499)	0.309^*(0.236~0.382)

Note: β Adjusted for age, sex, marriage, education level, occupation, monthly household income, chronic diseases, smoking, drinking, ADL. ^* P<0.05.

Bootstrap test results

We employed bootstrap testing to further validate the mediating role of chronic pain in the relationship between falls and frailty. For the entire population, the total effect of falls on frailty was 1.065 (95% bootstrap CI: 0.804~1.326), with a direct effect of 0.797 (95% bootstrap CI: 0.511~1.083) and an indirect effect of 0.268 (95% bootstrap CI: 0.170~0.366). Chronic pain partially mediated the effect of falls on frailty, explaining that approximately 25.2% of this effect can be attributed to mediating effects. In addition, we conducted separate analyses to examine the mediating effect of chronic pain on the relationship between falls and frailty across different ethnic groups, aiming to evaluate potential differences in this mediation among these groups. The results showed that within the Han population, chronic pain accounted for approximately 28.2% (indirect effect=0.335; 95% bootstrap CI: 0.171~0.499) of the total effect as a mediator between falls and frailty. In Zhiguo ethnic populations, chronic pain contributed to about 18.4% (indirect effect=0.190; 95% bootstrap CI: 0.008~0.372), of the total effect as mediator between falls and frailty. Among other minority populations, chronic pain explained approximately 21.5% (indirect effect=0.170; 95% bootstrap CI: 0.025~0.315) of the total effect as a mediator between falls and frailty. Detailed information is presented in Table 4.

Table 4. Bootstrap test results for different populations

Populations	Effect		SE	95% bootstrap CI	Mediation effect (%)
Whole sample (N=2710)	Total effect	1.065	0.133	0.804~1.326	-
	Direct effect	0.797	0.146	0.511~1.083	-
	Indirect effect	0.268	0.050	0.170~0.366	25.2%
Stratified by ethnic group
Han majority (N=814)	Total effect	1.185	0.228	0.737~1.633	-
	Direct effect	0.850	0.248	0.364~1.337	-
	Indirect effect	0.335	0.084	0.171~0.499	28.2%
Zhiguo minorities (N=1036)	Total effect	1.036	0.225	0.595~1.477	-
Zhiguo minorities (N=1036)	Direct effect	0.846	0.231	0.393~1.299	-
	Indirect effect	0.190	0.093	0.008~0.372	18.4%
Other minorities (N=860)	Total effect	0.791	0.232	0.336~1.246	-
	Direct effect	0.621	0.258	0.116~1.126	-
	Indirect effect	0.170	0.074	0.025~0.315	21.5%

Note: Effect, standardized regression coefficient. SE, standard error.

The primary objective of this study was to examine the mediating role of chronic pain in the association between falls and frailty among middle-aged and older adults residing in Yunnan Province, China. The findings revealed a high prevalence of falls, chronic pain, and frailty within this population, with a significant and noteworthy correlation observed between chronic pain, falls, and frailty. Specifically, it was found that chronic pain partially mediated the relationship between falls and frailty, exhibiting variations across diverse ethnic groups.

A striking revelation pertains to the higher prevalence of frailty symptoms (21.62%) among middle-aged and senior participants compared to a previous study conducted in the southwestern region, which reported a frailty prevalence of 12.7% among elderly individuals living in community settings[45]. Despite the disparate age ranges, this study highlights a considerably high occurrence of frailty among individuals aged 45 and above residing in ethnic minority areas. This discernment engenders a compelling proposition that frailty may manifest itself at an earlier chronological phase than hitherto believed and extend beyond the customary threshold of those aged 60 and above[46]. However, it should be noted that the higher prevalence observed in this study may be ascribed to a pronounced proportion of ethnic minorities inhabiting in rural areas, particularly among the Zhiguo ethnic minorities. This is where both the proportion of middle-aged inhabitants and the prevalence of frailty attain zenith. National census data indicates that Zhiguo ethnic minorities experienced shorter life expectancy than Han majority population, implying an increased likelihood of experiencing frailty at lower age groups within these ethnic groups[47]. Therefore, there exists a compelling rationale for further exploration into determinants influencing the onset, progression and deterioration of frailty among middle-aged and older adults from less developed areas.

Consistent with previous findings[48, 49], the present results suggest a significant association between falls and frailty among middle-aged and older adults irrespective of their ethnicity. In addition to physical injuries such as fractures and sprains resulting from falls, prolonged bed rest after a fall could negatively impact the daily activities and social interactions of fallers, thereby further exacerbating the occurrence of frailty[50, 51]. Hence, the imperative of fall prevention assumes paramount significance within the broader framework of frailty prevention. However, it is worth noting that participants in this study inhabited in rural areas and exhibited a low level of education. The determinants engendering their susceptibility to falls may differ from their urban or community-dwelling counterparts. Engaging in strenuous physical labor can lead to comparatively elevated levels of muscle quality and strength[52]. Nevertheless, as these individuals advance in age, they are susceptible to experiencing fatigue and muscle exhaustion due to the prolonged nature of their physical labor. This can be concomitant with the onset of pain in various regions of the body, thereby elevating their vulnerability to falls[53].

As suggested in previous study, the perception of falling among elderly individuals can substantively influence the incidence of falls[54]. Rural-dwelling elderly individuals tend to perceive falls as an inherent aspect of aging rather than a latent health peril. This perspective could engender a reluctance amongst older adults to seek assistance or adopt proactive preventive measures following a fall, consequently increasing their vulnerability to frailty[55].

Moreover, the accelerated process of urbanization over the preceding three decades in China has witnessed a substantial influx of large-scale migrant laborers into metropolises, coupled with a continuous upsurge in solitary living among elderly individuals nestled in rural areas or small towns[56]. This population often encounters heightened inconveniences, difficulties, and health risks compared to those residing with their adult children[57]. Consequently, they may exhibit an elevated proactivity for medical services, such as fall prevention and post-fall care, the facets that are currently insufficiently addressed by the prevailing healthcare system.

Our study unveils a crucial facet of the relationship between falls and frailty --- the mediating role of chronic pain. Specifically, we observed that chronic pain mediates 25.2% of the overall effect of falls on frailty, underscoring the significance of chronic pain in influencing frailty development. Previous research has shown that middle-aged and older adults who have experienced falls are more prone to developing chronic pain as a result of physical injury[17, 37]. Some older adults may even experience a post-injury pain syndrome characterized by prolonged discomfort at initially non-painful injury sites[58]. Furthermore, Chronic pain serves as a predictive indicator for frailty in middle-aged and elderly individuals, with higher pain intensity, chronic widespread pain, and greater pain interference associated with increased vulnerability to frailty[59-61].

Importantly, after accounting for the presence of chronic pain, the association between falls and frailty decreased from 1.065 (total effect) to 0.767 (direct effect), signifying a potential avenue for intervention. Integrating strategies for managing chronic pain into fall prevention approaches targeted at middle-aged and elderly individuals could play a pivotal role in mitigating frailty onset.

Subgroup analysis revealed variation in mediating effects among different ethnic groups. Within the Han majority subgroup, falls had a partially mediated impact on frailty through chronic pain, with a mediating effect of 28.2%. The subgroup comprising other minorities exhibited a second-level mediating effect of 21.5%, while the Zhiguo minority subgroup demonstrated the lowest mediating effect at 18.4%. These disparities can be attributed to several factors supported by existing literature. Firstly, differences in gene, physiology, and metabolism across racial and ethnic groups can influence pain sensitivity, tolerance, and reporting severity[62, 63]. Socio-cultural context and lifestyle also play significant roles; for instance, dietary patterns among seniors in ethnic minority areas may influence pain relief[64]. Additionally, diverse exercise habits and medication use within different ethnic groups could impact disease risks and chronic pain recovery differently[65]. Lastly, some ethnic groups prioritize family and community support more than others, leading to receive timely care when experiencing falls or pain[66, 67]. Notably, our study indicated a higher tendency for alcohol consumption among the Zhiguo ethnic minorities, which could potentially exert an analgesic effect on chronic pain, alleviating pain sensations[68].

While further research is essential to comprehensively elucidate the diverse impacts of chronic pain among different ethnic groups, our preliminary findings suggest that addressing chronic pain may hold varying degrees of importance in reducing frailty risk across these groups. This underscores the need for tailored interventions encompassing dietary therapy, medication management, physical therapy, and appropriate exercise regimens to effectively decelerate frailty progression[69, 70].

Limitations

Our study has certain limitations that should be acknowledged. Firstly, our study employed a face-to-face household survey method. Despite our best efforts to ensure the accuracy of the questionnaires, it is impossible to completely eliminate the potential for recall bias. Respondents were required to provide information on aspects such as chronic illnesses and household income, which may be susceptible to subjective memory and interpretation biases. Secondly, our study predominantly targeted an elderly population, potentially introducing language and communication barriers. To mitigate this issue, we enlisted assistance from family members of respondents for translation and communication purposes in order to optimize questionnaire quality. However, despite these measures being taken into account, we cannot entirely dismiss the potential impact of communication issues on data validity. Lastly, our study utilized cross-sectional data which limits establishing causal relationships between variables. Future longitudinal studies can further explore causal associations between these variables while considering additional potential confounding factors and temporal aspects.

The present study, conducted in a western province of China, involved a cohort of 2,710 middle-aged and older adults, representing a diversity of ethnic backgrounds. A noteworthy finding emerges from this study, revealing that approximately one-fifth of the participants exhibited frailty, while roughly one-tenth experienced falls within the preceding 12 months. Furthermore, half of respondents reported varying degrees of chronic pain. These findings highlight the interconnections between falls, chronic pain, and frailty among this specific population. Of particular significance, chronic pain emerged as a partial mediator in the relationship between falls and frailty with statistically significant effects observed across three subgroups by ethnic identity. In summary, this study provides valuable insights into the intricate nexus between frailty, falls, and chronic pain among middle-aged and older adults from diverse ethnic backgrounds in a western province of China. Consequently, this study underscores the potential utility of deploying effective management strategies targeting chronic pain and falls prevention as pivotal interventions to address frailty within this demographic.

TFI Tilburg Frailty Indicator

NRS Numerical Rating Scale

RMB Renminbi

ADL Activity of Daily Living

PADL Physical Activities of Daily Living

IADL Instrumental Activities of Daily Living

Acknowledgements

The authors thank all the participants of this study and generously shared their valuable opinions and feedback.

Authors’ contribution

XW and YH conceived the study. RD and YH supervised the data collection and managed the data, including quality control. XPW, CYD, XJL, YFZ and YC made their contributions to the acquisition, interpretation and analysis of the data. XW and RD drafted the original manuscript. YH made their contributions to revision of the work, and all authors reviewed, edited, and approved the final manuscript. YC and YH takes responsibility for the paper as a whole.

Funding

This study was supported by the Science and Technology Plan Project Science and Technology Department of Yunnan Province (202201AY070001-024); Yunnan High-level Talent Support Plan (YNQR-QNRC-2018-140) and Provincial Talent Program for Young Scholar and Technical Reserve Personnel (202305AC160046).

Availability of data and materials

The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.

Ethics approval and consent to participate

This study was approved by the ethics committee of the Kunming Medical University (NO. KMMU2021MEC095). At the beginning of the research, the researchers explained the project to the participants. The information included the aims of the study, potential advantages and disadvantages of participation, the expected benefits of carrying out the research, principles of privacy and confidentiality, and a declaration of voluntary participation. Participants were also informed that they could withdraw from the study at any time. The study was conducted in accordance with the Declaration of Helsinki, and all participants signed informed consent forms. For participants who cannot read and write, written informed consent was obtained from their legal guardians.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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No competing interests reported.

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The Mediating Effect of Chronic Pain on the Relationship between Falls and Frailty: A Cross-sectional Survey among Middle-aged and Older adults from Ethnic Minority Groups in Yunnan Province, China

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