Our findings corroborate the well-established evidence about the role of social factors in shaping socioeconomic health inequities. Based on a nationally representative sample of older Mexican adults, we observed that SEP, gender, and ethnicity were associated with different IC trajectories. In summary, we found that older adults with higher wealth and education, being men or non-indigenous, were more likely to have better trajectories than individuals with lower levels of wealth and education, being women or indigenous people. To the best of our knowledge, this study is the first attempt to examine the contribution of SEP, gender, and ethnicity to the socioeconomic health inequities associated even with the most inherent component of healthy aging: intrinsic capacity.
Our results suggest that SEP, using wealth and education as proxies, is a significant contributor to the process of healthy aging, reinforcing existing literature’s findings that these socioeconomic factors play crucial roles in determining health outcomes in later life and influencing the overall process of healthy aging [18, 29, 30]. However, previous studies have mainly evaluated the impact on functional capacity as a measure of successful aging. In contrast, we found that these disparities are even observable in the more comprehensive construct of intrinsic capacity.
In this study, we have used the novel concept of intrinsic capacity proposed by the WHO to reorient clinical practice and public policies associated with aging, and we have identified some degree of heterogeneity in their trajectories. The application of this concept represents several advantages for research and health policies in aging. First, intrinsic capacity is a comprehensive measure of health, which can be monitored throughout the life course and advocates for maintaining functional capacity in older adults, regardless of the presence of diseases [31]. Second, it focuses on functional capacity and its preservation rather than on the deficiencies of old age or the deterioration of bodily functions [32]. Third, it emphasizes identifying individual attributes associated with functionality and the influence of the environment in which people live [33]. These characteristics favor comparisons between countries and cultures about healthy aging and identifying contextual attributes that affect intrinsic capacity [34]. In this latter sense, customary monitoring of intrinsic capacity through longitudinal trajectories, for example, could help in early warning about a decline in functionality and inform potential preventive interventions.
The results of this study must be framed in the context of a middle-income country such as Mexico. Aging in Mexico has occurred amid a fragile economy marked by high levels of poverty and limited access to health services and resources [35]. This situation is further aggravated by the high prevalence of chronic conditions such as hypertension, diabetes, and hypercholesterolemia, but also by the presence of health conditions that mainly affect older adults, such as frailty, sarcopenia, and functional dependence, combined with conditions related to nutritional status like overweight/obesity and anemia [36]. Additionally, evidence shows that Mexican older adults from the most disadvantaged socioeconomic groups have worse health and nutritional conditions [37]. Despite these circumstances, our data show that 33% of older adults in Mexico maintained or even improved their intrinsic capacity over an 8-year observation period (2009 to 2017). This fact could be partially explained because, during the last 40 years, Mexico has implemented programs at the national level to alleviate poverty through conditional transfers [38], increase the coverage of health services [39], reduce food insecurity [40], and improve older people’s income through non-contributory pensions [41]. All in all, the results of our study show that significant inequalities (economic, gender, and ethnicity) associated with intrinsic capacity persist.
The beneficial effects of wealth and education can be attributed to several socio-biological mechanisms. Higher levels of education are generally linked to better health literacy and healthier behaviors during the entire life [42, 43], with variable impacts throughout the life course [44], which jointly affect health outcomes in late life. In addition, higher wealth and income (both related to education) may enable older adults to access better healthcare services and maintain healthier lifestyles [45]. In contrast to previous studies, our study notably underscores the role of socioeconomic factors in shaping the inherent potential for healthy aging. Our findings suggest that disparities, when manifested as differences in resources and opportunities, could profoundly affect this potential for aging healthily.
Gender and ethnic disparities in IC trajectories observed in our study further highlight the presence of health inequities in older adults. Women and indigenous individuals were found to be more likely to follow a steeply declining IC trajectory. This finding could be due to several factors, including differential access to resources, cultural barriers to healthcare, and systemic discrimination. Evidence has shown that women around the globe have a lower power position, less wealth and property, a higher burden of work of informal caring, less education, are employed in lower-paid jobs, and have less access to retirement benefits. Indigenous people have been systematically marginalized and isolated; they are poorer, with fewer years of education, less access to healthcare services, and higher unemployment rates [46,47,48,49]. These findings echo other studies that have reported gender and ethnic disparities in health-related outcomes. For instance, women lose more Disability Adjusted Life Years (DALYs) than men in reproductive infections, HIV, cancers, migraine, mental health, eye disorders, dementias, nutritional disorders, and muscle and bone conditions. Indigenous peoples have a lower life expectancy, higher infant mortality rates, infectious diseases like tuberculosis, diabetes, cancer, malnutrition, and a higher risk of mental illness like post-traumatic stress disorder and social phobia [50,51,52,53]. Our results underscore the need for targeted interventions to address these health inequities in early life and emphasize the need to identify the determinants of these gender and ethnic inequities, which can be modifiable by reducing gender and ethnic discrimination, that affect participation in the overall structure of opportunities and access to resources (education, healthcare services, etc.) throughout life [54].
Aside from the mechanisms just described, it has recently been suggested that health inequities are manifested in worse health through intermediate biological processes. Specifically, socioeconomic disadvantages associated with SEP, gender, and ethnicity may be related to chronic stress that impacts chronic conditions modulated by physiological wear and tear due to inflammatory responses, impaired immune function, and epigenetic acceleration of aging [55]. Furthermore, research suggests that SEP could be associated with allostatic load (a composite measure of overall physiological strain), a significant result since it has been suggested that allostatic load could represent the biological substrate of intrinsic capacity [56].
This study has some limitations that warrant consideration when interpreting findings. First, we could not examine the trajectories of intrinsic capacity before the onset of old age. Future studies should investigate its behavior throughout the lifespan, identifying the effects of inequities at different stages of life. Second, our analysis did not consider other social determinants, such as occupation, geographical location, and access to healthcare services. Third, we focused on gender and ethnicity because we know that they do not change over time, and wealth captures the accumulation by the time individuals reach older adulthood. However, this social determinant would likely change over time. Forth, exploring the impact of other individual and collective social determinants on intrinsic capacity, and identifying their mechanisms, is a pending task that likely requires more prolonged periods of observation, considering cohorts from youth and conducting more measurements over time.
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