This study represents the first attempt to evaluate the association between TDI and frailty in a large population (> 26,000 participants), demonstrating a significant relationship between TDI and frailty. The consistent and significant associations between TDI and frailty were observed across all subjects as well as within subgroups stratified by sex and age, Furthermore, Inflammation indicators and mental health mediated the associations between socioeconomic deprivation and frailty status. These findings collectively highlight the importance of socioeconomic deprivation as a risk factor for frailty among middle-aged and older adults.
Previous studies have reported that socioeconomic position, neighborhood deprivation were associated with frailty[11, 12]. However, these studies did not assess the association between TDI - a newly developed representative index for measuring socioeconomic deprivation - with frailty. Therefore, our study first reported the correlation between TDI and frailty. Our significant associations using TDI were consistent with those obtained using other indices, suggesting socioeconomic deprivation has import effect on frailty. underscoring the substantial impact of socioeconomic deprivation on frailty risk. Additionally, we identified a dose-response relationship indicating that higher levels of social deprivation are associated with an increased risk of pre-frailty and frailty development. Importantly, these findings remain robust even after adjusting for potential covariates such as body mass index.
We observed that socioeconomic deprivation has a greater impact on men's health than on women's. This finding on deprivation and the odds of frailty in females and males is consistent with data from the World Health Survey[13], which found that higher levels of household economic status were significantly associated with self-reported health for men. However, for women, this positive association was only significant in the fourth and fifth wealthiest quintiles.
Socioeconomic deprivation not only reflects the economic status of the population, but also objectively describes the unequal distribution of socioeconomic resources. High levels of socioeconomic deprivation are characterized by low healthcare resources, unhealthy lifestyles, and poor living and working environments[14]. Possible causes for the observed relationship between socioeconomic deprivation and frailty include both the physical environment (e.g., environmental degradation and proximity to major roads[15]) and the characteristics of the neighborhood (e.g., perceived safety[16]). These socioeconomic factors can cause the body to react in a way that triggers frailty.
Previous studies have consistently demonstrated that individuals experiencing high levels of socioeconomic deprivation are more prone to chronic inflammation, and the underlying pathways are likely to be intricate [17]. For instance, individuals with high levels of socioeconomic deprivation are more susceptible to be exposed from external triggers of inflammation, such as silica and asbestos particles, in their living and working environments. In vivo, when macrophages encounter foreign substances, it activates the NALP3 inflammasome leading to an inflammatory response[18]. Higher levels of inflammatory markers in the bloodstream have been associated with increased muscle mass and strength decline, accelerated loss of mobility, lower limb function, and physical activity impairment, as well as depression among older adults. All these factors constitute essential components for defining frailty based on commonly used criteria in literature[19]. Furthermore, inflammation contributes to accelerated aging in patients with multimorbidity[20]. Not surprisingly, a majority of frailty patients experience chronic inflammation. Previous research along with the findings presented herein suggest the existence of shared bio-behavioral pathways that may underlie variations in higher levels of inflammatory markers and frailty.
The mental indicators involved in this study show significancant mediation effects, indicating that they play a significant and partial role in mediating the associations. Wilson et al.[21] conducted a study of 5222 community residents, and their findings indicated that a high Townsend deprivation index was associated with an increase in the prevalence and incidence of depression. A Genome-wide Gene-by-Environment Interaction Analysis identified multiple candidate loci interacting with the TDI that were related to neural or brain development[22]. Socioeconomic deprivation has been demonstrated as a risk factor for poor mental health[17, 23, 24]. Furthermore, Mutz et al[25]. showed that higher levels of frailty in individuals with mental disorders. Individuals with a mental disorder have a higher risk of all-cause mortality compared to the comparison group without mental disorders. These studies, together with ours, suggest that the relationship between socioeconomic deprivation and frailty may be mediated by depressed, lonely mood states.
This finding has potentially significant implications for public health. Data from systematic review studies suggest that frailty is a strong predictor of hospitalization and mortality[26, 27]. For example, in a previous report, a 0.1 increase in frailty index score was associated with a 28% increase in the odds of dying. Targeting the most deprived segment of the population with interventions is the best chance of benefiting, for example, anti-inflammatory treatment and psychological interventions. This includes the need for governments to provide more socioeconomic and medical resources to the deprived populations.
Several limitations need to be considered. Firstly, the cross-sectional nature of the study precludes making causal inferences. Prospective studies are required to evaluate the association between socioeconomic deprivation and frailty. Secondly, most of the exposure and mediating information included in this study was self-reported, potentially introducing recall bias [28]. However, it is important to note that the questionnaires employed for data collection have been validated by numerous studies[8, 10, 29, 30]. Thirdly, the mediation technique utilized in this study imposes a constraint whereby only one mediator can be included at a time[31, 32], which may underestimate potential mediation effects and hinder comprehensive exploration of the relationship between socioeconomic deprivation and frailty (e.g., investigating combinations of mediator variables across different groups such as lifestyle factors, psychosocial aspects, and biological markers). Although examining individual mediators alone cannot fully elucidate the complex association between socioeconomic deprivation and frailty, it aids in identifying contributing factors within this intricate relationship. Moreover, it should be acknowledged that considering multiple mediators simultaneously increases the likelihood of Type 1 error[33]. Therefore, future research necessitates further investigation into alternative techniques to unravel mechanisms underlying this multifaceted association.
This study suggests that socioeconomic deprivation is associated with frailty in middle-aged and older individuals in the UK, and that this association can be mediated by chronic inflammation and mental health. The findings provide potential targets for prevention in patients with frailty. Community deprivation imbalances should be taken into account in policy development when endeavoring to reduce health inequalities in the aging population. More importantly, it contributes to the evidential framework for exploring the biological mechanisms of frailty in the elderly. We have identified the role of chronic inflammation and some of the psychiatric indicators, there may be many other biological mechanisms underlying the observed associations. These processes are not necessarily mutually exclusive and could be closely intertwined.