Introduction

According to estimates of the World Health Organization (WHO), adults over 60 years of age are the fastest growing age group, to the point that they currently outnumber all children under five and, by the year 2050, they are projected to outnumber people aged between 15 and 24 ¹. These data indicate significant changes in the distribution of population groups and in global demographic dynamics due to increased longevity ^1,2.

In 2015, the United Nations (UN) reported that, in Latin America and the Caribbean, 11 % of the population was over 60 years of age and that, within 35 years, one out of every four people will belong to that age group ³. Consequently, in Peru, the Instituto Nacional de Estadística e Informática del Perú (INEI - National Institute of Statistics and Informatics of Peru) has estimated an average annual growth rate of 4.9 % for the last 10 years so that, by 2050, one out of every five people will belong to the group of older adults ⁴.

Together with population aging, depressive disorder in old age is a serious risk of overburdening the health care system, social security and the economy, in addition to affecting individual well-being ^5-7, especially considering that depression is one of the most common mental illnesses in this age group and is related to the development and unfavorable prognosis of other chronic diseases ^8-10. This is why a better understanding of depressive disorder in old age is important from a clinical and public health perspective.

Current evidence demonstrates a relationship between disability and mental health, including an increased risk of depression ^9-12. However, not only pathophysiology and related mechanisms are not yet fully understood, but other factors may influence this relationship ^13-20, as established by the WHO Commission on Social Determinants of Health (CSDH) that addresses the reasons that may lead to avoidable health inequities ²¹. Several studies have related sociodemographic aspects to depressive disorder among older adults and found variations according to the distinctive features of each society ^15-19.

In Peru, the population aged 60 years and older accounted for the highest percentage of people with a disability between 2000 and 2019 ²², while the trend of depressive disorder increased after age 75 ²³. Moreover, Peru ranked third in the Americas in the classification of disability due to depression, with 8.6 %, which exceeds the regional average of 7.8 % ²⁴. These data indicate not only the potential impact of neglecting depressive disorder and its relationship with disability in the health system and the quality of life of Peruvians but also the importance of improving the understanding of the limitations of the older adult population for the eventual development of more efficient public health policies.

Given the evidence suggesting a variable influence of the sociodemographic factors of depressive disorder, according to the distinctive features of each population, as well as an association between physical disability, general comorbidities and depression in populations over 60 years of age, the present study aimed to identify the prevalence and factors associated with depressive disorder among

older adults based on data recorded in the 2019 Encuesta Demográfica y de Salud Familiar (ENDES - Demographic and Family Health Survey).

Materials and methods

Ethical considerations

The present research did not require the approval of an ethics committee, consents or additional permissions, since it analyzed a public domain database that does not allow the identification of the participants and is available on the INEI website (http://iinei.inei.gob.pe/microdatos/).

Figure 1 Flowchart of the screening of adults over 60 years of age included in the study. 2019 ENDES 

Results

The present study included a total of 4,174 older adults, out of whom 13.18 % had depressive disorder and 7.86 % suffered from a disability. Likewise, 53.33 % of the older adults were males, 74.79 % were in the 60-74 age group, 59.82 % had primary education, 83.87 % had health coverage, 41 % belonged to the geographic region of the highlands, 36.37 % were registered in "The poorest" wealth quintile and 60.57 % lived in the urban area. Moreover, a prevalence of 1.94 % was identified for smoking and 22.88 % for alcohol consumption (Table 1).

The analysis of the prevalence according to the study variables showed that depressive disorder was more frequent among female older adults (p = 0.000), those belonging to the age group over 85 years (p = 0.000), people with no education (p = 0.000), those having joined a health system (0.010 %), those belonging to the geographic region of the highlands (p = 0.000), those registered in the "The poorest" wealth quintile (p = 0.000), those living in rural areas (p = 0.000) and those suffering from a disability (p = 0.000). As for bad habits, alcohol consumption showed a statistically significant difference (p = 0.001), while smoking did not (p = 0.375) (Table 2).

Using the analysis for the calculation of prevalence ratios (PR), the crude model showed an association between depressive disorder and all variables, with the exception of belonging to the geographic region of the jungle (p = 0.076) and the rest of the coast (p = 0.726) with respect to Lima Metropolitan Area, as well as smoking (p = 0.386). However, in the adjusted model, there was no association between belonging to the 75-84 age group with respect to the 60-74 age group (p = 0.085), having joined a health insurance plan (p = 0.151), belonging to the geographic region of the highlands compared to Lima Metropolitan Area (p = 0.202), belonging to the "Poor" quintile with respect to "The poorest" quintile (p = 0.146), living in the urban area versus the rural area (p = 0.604) and no alcohol consumption (p = 0.435) (Table 3).

Older males were less likely to suffer from a depressive disorder (aPR = 0.602; 95 % CI: 0.513-0.706) than females, and the group over 85 years of age showed a higher risk than those from 60 to 74 years (aPR = 1.664; 95 % CI: 1.304-2.124). Besides, not presenting a disability behaved as a preventive factor (aPR = 0.542; 95 % CI: 0.440-0.668), while the variables educational level and wealth quintile, starting from the "Middle" quintile, were protective factors when taking the categories "No education" and "The poorest" as reference (p < 0.005), respectively (Table 3).

Discussion

According to the research results, the prevalence of depressive disorder among older adults accounted for 13.18 %, which suggests a reduction compared to previous years ^9,10. This decrease could be due to the implementation of mental health strategies, mainly the implementation of community mental health centers ⁶. Likewise, the distribution of the older adult population follows the parameters of the region, which shows an international demographic aging pattern ^1-4.

Similarly, the correlation between depressive disorder among older adults and gender is consistent with that of previous studies, in which female sex is a risk factor ^8-15. It is noteworthy that in studies carried out in the Peruvian older adult population ^9,10, as well as in other Latin American countries ⁸, depressive disorder is more correlated with females than with males. Likewise, Richardson, et al. ¹⁵ recorded the female sex as a risk factor for depressive disorder among older adults from 18 different countries in Asia, Europe and America. According to the available evidence, this susceptibility could be due not to biological factors but to determining factors derived from gender roles that predispose females to express and acknowledge their emotions more openly than males; to develop a lower capacity to accumulate wealth and receive education and an income than males; to have a more fragmented career path; to experience the loss of a spouse, loneliness, social isolation, disability and economic hardship. These factors would lead, toward the end of life, to live in environments where rates of psychological distress are high ^13,14. Even so, adjusted correlation models indicate that, beyond gender per se, there are sociodemographic aspects that may condition the prevalence of depressive disorder and act as protective factors for female older adults.

The risk factor for those over 85 years of age is an indicator likely to increase. Although this age group currently accounts for a minority percentage, given the demographic dynamics of aging in the country, it is possible that its number will increase exponentially each year ³. A total of 26.27 % of older adults in this age range had depressive disorder, which is more than double the percentage of the reference group and suggests that, in an eventual increase, the prevalence of depressive disorder will also increase, as recorded in other populations where life expectancy increased ¹².

On the other hand, the behavior of the educational level and wealth quintile as protective factors implies the influence of situations beyond the scope of health care on the state of mental health. Thus, although recent public health strategies have included with special emphasis the treatment and prevention of the most prevalent diseases in the framework of mental health ^6,7, the results of the

present research show that joining a health insurance plan is neither a significant factor nor a preventive factor for depressive disorder, even more if it is considered that 83.87 % of the older adults had health coverage. The magnitude of insured older adults shows that the care provided for the treatment and prevention of depressive disorder is not achieving the desired impact, although the multifactorial nature of the problem makes it difficult to predict the effect that mental health services, by themselves, can achieve ^15,27.

In this sense, an association between unfavorable socioeconomic conditions and 1.8 more probabilities of suffering from depression, compared to groups in better conditions, has been found. This same pattern is reflected in research studies conducted in different populations ^15-19. Even so, the various correlations may be due to cultural differences between countries. Freeman et al. ¹⁶ found an incidence of depressive disorder of 9 % in Spain in the context of a national financial crisis and an unemployment rate twice that of Poland and Finland, where the incidence of depressive disorder accounted for 4 %. Despite this, they found no association between income levels and depressive disorder in Spain, in contrast to Poland and Finland. Likewise, Ettman et al. ¹⁸ determined that the inverse relationship between income levels and depression will depend on macroeconomic events that condition the social dynamics in each country, so that a condition such as the increase in real estate prices will have a greater negative impact on the mental health of older adults living in cities where there is a greater lack of access to housing.

Concerning the Peruvian situation, the data reported by the INEI could offer an approach to the conditions of this age group. According to 2021 statistics, 83 % and 70 % of the female and male older adult population, respectively, have some chronic health problem; 53 % of older adults are economically active; 25.9 % of Peruvian households are headed by an older adult (out of whom 16.2 % have joined a social welfare program); and 92.2 %, 74.5 % and 95.2 % have access to public water supply, public sewage and electricity, respectively ⁴. These indicators cover the basic needs related to economic stability, which could explain why out of all the factors evaluated, the wealth quintile showed the highest correlation. Even when considering the high incidence of chronic diseases, the total percentage of depressive disorder was only 13.18 % (Table 1). A decreased risk of depression was found for older adults belonging to higher wealth quintiles; on the other hand, there was no correlation with factors such as bad habits, health coverage and area of residence (Table 3). This suggests that the socioeconomic factor has even a greater impact than chronic conditions; likewise, the educational level acts as a protective factor, which can be associated with a better understanding of the stage of life and a greater probability of increasing socioeconomic well-being ^17,19. These criteria highlight the importance of strengthening the indicators of economic well-being and education in the general Peruvian population.

It is also important to note that alcohol consumption and smoking were not risk factors for depressive disorder, unlike suffering a disability. This may be due to the constant global policies to break bad habits ^28-30 and the decreased general activity associated with older age ^5,13,19, which are reflected in the descriptive statistics of the present study, which recorded a prevalence of 1.94 % and 22.88 % for smoking and alcohol consumption, respectively. On the other hand, although not suffering a disability is a protective factor (aPR: 0.542; 95 % CI: 0.440-0.668), such result could be attributed to the fact that the prevalence of disability found among older adults was 7.86 %. Even so, there is sufficient evidence to establish a relationship between depression and disability. Disability itself is an independent determining factor of the severity of depressive symptoms in different health conditions, including hypertension and diabetes, and could play the role of a chronic stressful condition that in turn increases the risk of developing depression ^10,11. In addition, depression has been linked to high cortisol levels that physical exercise could modulate, which means that older adults with some disability would be prevented from receiving an adequate therapy ²⁰. Such conditions could explain the results of the present study and delve into the nature of the disability. Martina et al. ⁹ found that 12.7 % of the Peruvian population over 60 years of age with a disability had some degree of depression, as well as a correlation between both variables. Similarly, Barboza et al. ¹⁰ recorded a correlation when the depressive disorder was moderate or severe. This difference allows highlighting the importance of the degree of depressive disorder in the association with the disability. Given the reciprocal nature of disability and depression, it is possible that, in chronic conditions, extreme physical limitations may lead to depressive disorder or that, in severe depressive conditions, physical disability may be part of the symptoms of the disease ^11,20. The measurement instruments for depression and disability should also be considered, in addition to factors such as the sociocultural valuation given to physical capacity of the study population.

Among the limitations of the research it is worth mentioning that, since it was a secondary analysis, other variables of interest could not be included. Moreover, it was not possible to develop causal relationships due to the crosssectional design of the study. However, the representative quality of the data obtained from the ENDES makes it possible to establish the correlation between the incidence of depression and physical disability, general comorbidities and sociodemographic factors at the national level, using a methodology validated by the INEI.

It is concluded that there is a low percentage of depressive disorder among Peruvian older adults, as shown by a decrease registered since 2014. Likewise, belonging to the group over 85 years of age, being a female, suffering from a disability, belonging to lower wealth quintiles and having a lower educational level predispose older adults to have depressive disorder.

It is recommended to conduct studies to evaluate the incidence of depressive disorder among older adults, within their own demographics and social environment, in order to identify their specific limitations, as well as addressing mental health treatment through health strategies that are not implemented in isolation but in relation to policies aimed at modifying the sociodemographic factors of the population.