Depression, one of the most common mental disorders, affects more than 264 million people worldwide (1, 2) and leads to more than 50 million Years Lived with Disability from 1990 to 2017(3). Depressive disorder often results in cognitive impairment, sleep disorders, dementia, and even suicide, causing a serious burden to the individual, family, and society (4–6). Several epidemiological studies demonstrated that people who experience depressive symptoms might have an increased risk of a variety of illnesses, disabilities, and death, even without a formal diagnosis (1, 7). Moreover, without efficient intervention for existing depressive symptoms, undiagnosed depression symptoms might lead to progression and a more serious disease burden (8).

China has experienced an aging society since the end of the 20th century, with the aging trend taking a toll on public healthcare systems. According to the seventh National Census of China, people aged 65 years or above accounted for 13.50% of China's population in 2020. The proportion of the elderly population has increased by 4.63% in the last decade (9). A meta-analysis published in 2018 suggested that about 2.7% of elderly adults have suffered from a major depressive disorder (10). Moreover, middle-aged adults are rapidly entering the ranks of the elderly. The middle-aged population is also suffering from decreased mental health (11). For example, Choi et al. conducted a longitudinal study in Korea and found that 35.1% of middle-aged adults (aged from 45 to 54 years old) had depressive symptoms (12). Given the aging society and increasing mental health problems of middle-aged and older adults, identifying risk factors for depression is of great significance for mental health promotion in the middle-aged and elderly populations in China.

Mental health might be affected by a combination of individual, family, and environmental factors, and it is not easy to find a comprehensive indicator covering all aspects of those factors (13–15). Satisfaction is a comprehensive psychological index to evaluate the difference between expectation and perception. Several studies reported that many satisfaction aspects are associated with mental health. For example, a Canadian national survey suggested that life satisfaction was strongly associated with self-reported mental health (16). Marital relationships could also affect people's mental health. A study involving 728 women suggested that greater marital satisfaction was associated with fewer depression symptoms (17). The relationship between parents and their children may also affect the parents' mental health. For example, Chen et al. showed that parent-child relationship satisfaction was negatively associated with depressive symptoms and diagnosed depression (18). Finally, air quality and health conditions might be important factors for mental health. Although the associations between air quality satisfaction, health satisfaction, and depression may not have been examined, numerous studies suggested that people experiencing higher levels of air pollution (16–18) and worse health conditions (19, 20) are more likely to suffer from depression and other mental health problems. Based on the abovementioned studies, we proposed a hypothesis that satisfaction with life, health, marital status, parent-child relationship, and air quality might be associated with depressive status.

To the best of our knowledge, no study has comprehensively explored the effects of satisfaction with life, health, marital status, parent-child relationship, and air quality on depressive symptoms. To fill this gap, the present study aimed to explore the relationship between five dimensions of self-reported satisfaction and depressive symptoms. The research hypothesis of our study is shown in Figure 1. We focused on (1) the prevalence of depressive symptoms among the Chinese middle-aged and elderly populations; (2) the associations between each aspect of satisfaction and risk of depressive symptoms; and (3) whether these relationships differ among populations with different characteristics.

After excluding 5,791 participants with a missing depressive score or satisfaction assessment data, and 47 participants without vital demographic characteristics, a total of 13,978 middle-aged and elderly adults were included in our study. The sample range covered 126 county-level cities in 28 provinces of China, and the distribution of participants is presented in Figure 2. The mean age of participants was 60.48 ± 18.82 years. Among them, 7,012 (50.2%) participants were men. Most of the participants lived in rural areas (59.6%), reported low (elementary school or below) education levels (61.2%), were married and living with a spouse (89.0%), and were categorized as non-smokers (93.5%) and non-drinkers (63.3%). Moreover, 36.2% of the participants were recruited from East China, 38.8% were from Middle China, and 25.0% were from West China. A total of 4,986 participants scored 10 points and above, giving a prevalence of depressive symptoms of 35.7%. More detailed information regarding the participants is shown in Table 1.

Table 2 presents the average score of all five dimensions of self-reported satisfaction and depressive status. The mean levels of life, health, marital status, parent-child relationship, and air quality satisfaction were 3.28 ± 0.77, 2.97 ± 0.90, 3.43 ± 0.81, 3.64 ± 0.71, and 3.16 ± 0.82, respectively. In terms of depressive status, the mean CESD-10 score was 8.24 ± 6.39. Pearson's correlation test suggested that a high correlation existed among different satisfaction dimensions (Supplementary Table S3).

Figure 3 presents the associations between all five dimensions of satisfaction and the risk of depressive symptoms. Higher levels of life, health, marital status, parent-child relationship, and air quality satisfaction were all strongly related to a lower risk of depressive symptoms in model 1. When considering the potential confounders in the models, the results were still significant for these five dimensions of satisfaction (Model 2 and Model 3). After adjusting for sociodemographic factors, health behavior factors, and regional differences, we found that each 1-point increase in life, health, marital status, parent-child relationship, and air quality satisfaction was associated with 60.8% (OR = 0.392; 95% CI: 0.370, 0.414), 56.3% (OR = 0.437; 95% CI: 0.418, 0.458), 41.8% (OR = 0.582; 95% CI: 0.555, 0.610), 37.2% (OR = 0.628; 95% CI: 0.596, 0.662), and 25.6% (OR = 0.744; 95% CI: 0.711, 0.778) decrease in the risk of depressive symptoms, respectively (Figure 3).

Figure 4 and Supplementary Table S4 show the associations between self-reported satisfaction and depressive symptoms, stratified by age, sex, residence, education level, marital status, smoking status, drinking status, and regional categories. Participants younger than 60 might be more susceptible to depressive symptoms than the others, although there was mostly no statistical significance. For example, each 1-point increase in life satisfaction was associated with a 61.6% (OR = 0.384, 95% CI: 0.357, 0.413) decrease in depressive symptoms among people aged <60 years old, while this effect estimate was 59.7% (OR = 0.403, 95% CI: 0.375, 0.423) in people aged 60 years old or above. Moreover, our results suggested that participants with different residence, educational levels, marital status, and regional categories might have different effect estimates in some dimensions of satisfaction. For example, life satisfaction had a stronger effect on depressive symptoms among urban residents (OR = 0.356, 95% CI: 0.331, 0.384) than that of rural residents (OR = 0.414, 95% CI: 0.385, 0.445). Compared with participants with an elementary school or below educational level (OR = 0.408, 95% CI: 0.380, 0.438), people with a college degree and above were more sensitive to life satisfaction (OR = 0.253, 95% CI: 0.186, 0.326). Marital status might also modify the relationship between marital satisfaction and depressive symptom risk. Compared with participants who were married and living with a spouse (OR = 0.547, 95% CI: 0.514, 0.580), single people, divorced, or widowed were less susceptible to depression symptoms (OR = 0.583, 95%CI:0.533, 0.637). In addition, we found that the regional category might interact with life satisfaction and health satisfaction. For example, compared with people lived in East China (OR = 0.380, 95% CI: 0.356, 0.405), people living in Middle China (OR = 0.449, 95% CI: 0.422, 0.477) or West China (OR = 0.487, 95% CI: 0.457, 0.519) had a greater effect on people's health satisfaction.

This large-scale nationwide study suggested that the prevalence of depressive symptoms was 35.7% among Chinese middle-aged and elderly populations. Higher levels of life, health, marital status, parent-child relationship, and air quality satisfaction were related to a lower risk of depressive symptoms. For each 1-point increase in life, health, marital status, parent-child relationship, and air quality satisfaction, the risk of depressive symptoms would decrease by about 60.8, 56.3, 41.8, 37.2, and 25.6%, respectively. Additionally, we observed that participants who were aged <60 years old, were men, lived in an urban area, had higher-level education, were married and living with a spouse, did not smoke, drank alcohol, and were from East China might be more vulnerable to the risk of depressive symptoms than the others for several satisfaction dimensions.

Several epidemiological studies also examined the association between depressive status and individual satisfaction dimensions, mainly aimed at life satisfaction and marital satisfaction. As a composite measure of satisfaction, life satisfaction has been proven to have good psychometric properties and is associated with depressive status. For example, a cross-sectional study conducted in Poland showed that higher levels of life satisfaction were related to lower levels of depression in older adults (27). Similar results were observed among elderly Chinese. A cross-sectional study of 590 empty-nest and non-empty-nest Chinese elderly adults showed that depression was the strongest predictor of life satisfaction, even compared with physical health (28). Similar associations were reported in marital satisfaction research (29–31). A cross-sectional study investigating 141 infertile couples in Iran indicated that marital satisfaction was related to depression in both male and female participants (29). In terms of parent-child relationships, a cross-sectional study of middle-aged children and their fathers in the US, which used the data from the Family Exchanges Study (FES), found that lower satisfaction regarding their relationships with their children was associated with a higher risk of depressive symptoms (32). These associations between life, marital status, and parent-child relationship satisfaction might be explained by their associations with emotional support, family function, social capital, and primary care support (33–38).

Although we did not find any direct evidence for air quality and health satisfaction, numerous epidemiological studies suggested that people experiencing a higher level of air pollution exposure and worse health conditions were more likely to be depressed. For example, a meta-analysis conducted using five studies found that each 10-μg/m³ increase of PM_2.5 exposure (particulate matter with a diameter <2.5μm) was associated with a 10.2% increased risk of depression (OR = 1.102, 95% CI: 1.023, 1.189) (39). Similar results were observed for depressive symptoms. A cross-sectional study in middle-aged and elderly adults found that the incidence of depressive symptoms increased by 9% (OR = 1.09, 95% CI: 1.05, 1.14) for every 10-μg/m³ increase in PM_2.5 exposure (26). The mechanisms by which air quality affects depressive status might be that air pollutants would lead to oxidative stress, immune changes, dopamine depletion, and autonomic nervous disorders, resulting in depression (40, 41). In terms of health conditions, some studies showed that people with a disease suffer a higher risk of developing a depressive disorder. For example, a British study reported a positive association between depression and ischemic heart disease risk among male adults (42). On the one hand, a depressive disorder could lead to inflammation, changes to platelet pathways, and autonomic nervous dysfunction, causing an increased risk of other diseases (34, 43, 44). On the other hand, people with other diseases are also likely to smoke and drink alcohol and often do not cooperate with medical treatments, leading to a depressive disorder (43, 45).

In the stratified analysis, it is worth noting that all five dimensions of satisfaction had a consistent trend in depressive symptoms among people with different characteristics, even if there was no statistical significance. For example, we noticed that people younger than 60 years old were more sensitive to depressive symptoms than people aged 60 years old or above. We hypothesized that this might be because people aged <60 years old would take on more family responsibilities and have higher working pressure before retirement. Consistent with the results of our study, a meta-analysis that pooled 18 studies showed that the prevalence of depression was significantly higher among older urban adults than older rural adults (46). However, considerable heterogeneities existed among the included studies, and several suggested that people in rural areas suffer a higher risk of depression (47, 48). Further studies should be conducted to explore China's urban-rural differences in depressive status. In terms of the effect value, we noticed that participants with a higher education level have significantly higher effects in the associations between all five aspects of satisfaction and the risk of depressive symptoms. A potential explanation is that more educated people might have better medical care and financial support, which could attenuate the effects of satisfaction on the risk of depressive symptoms (49, 50). Moreover, we observed that the effects of participants from East, Middle, and West China decreased in sequence, which might be explained by the fact that people in more developed areas may suffer higher life and work pressures.

Living in a society, people's mental health might be affected by a combination of individual, family, and environmental factors. Our study explored the effects of five dimensions of satisfaction on depressive symptoms, which could be classified as one comprehensive dimension (life satisfaction), one individual dimension (health satisfaction), two household dimensions (marital status and parent-child relationship satisfaction), and one environmental dimension (air quality satisfaction). Our study might provide a more comprehensive understanding of depressive conditions and their risk factors. The results for participants enrolled from 126 county-level cities in 28 provinces of China could better reflect the real depressive condition of Chinese middle-aged and elderly adults. However, several limitations of this study should be mentioned. First, depressive status and satisfaction were assessed using self-reported data. Thus, the results only reflect mental health to some extent and are not equivalent to clinically diagnosed measures. However, the CESD-10 has been adopted widely in population-based depression status investigations, and the self-reported data allow the participants to answer survey questions according to their most contributed experiences to depressive status (49). Second, we examined the associations between five dimensions of satisfaction and depressive symptoms; however, other dimensions of satisfaction, such as security and job satisfaction, need further discussion. Third, demographic characteristics, smoking, and drinking behaviors of the participants were collected using a self-reported questionnaire; therefore, reporting bias, recall bias, and misclassification might exist in our study. Fourth, the cross-sectional design is inadequate to determine causal relationships between different dimensions of satisfaction and the risk of depressive symptoms. Longitudinal studies, such as cohort studies, would be expected to confirm our results. Finally, the findings of the stratified analysis need to be taken with caution because there was mostly no statistical significance. Further studies are needed to verify our findings.

This study demonstrated that more than a third of Chinese middle-aged and older adults had developed depressive symptoms. High levels of satisfaction with life, health, marital status, parent-child relationship, and air quality were associated with decreased risk of depressive symptoms in Chinese middle-aged and older adults. Given the aging society and increasing mental health problems of middle-aged and older adults, our findings provide a comprehensive basis for depression prevention and mental health improvement.

Publicly available datasets were analyzed in this study. This data can be found here: http://charls.pku.edu.cn.

The studies involving human participants were reviewed and approved by the Institutional Review Board at Peking University (Code: IRB00001052-11015). The patients/participants provided their written informed consent to participate in this study.

ZN, FZ, and ZD contributed to the conception and design of the study. ZN, FZ, SH, and FY conducted the experiments and organized the database. ZN, ZD, and XZ performed the statistical analysis. ZN and FZ wrote the first draft of the manuscript. WW, DH, KZ, ZD, and WQ revised the manuscript. All authors have approved the final version. All authors contributed to manuscript revision, read, and approved the submitted version.

This work was supported by grants from the National Natural Science Foundation of China (Nos. 81772734; 82102322) and the Innovation Capability Support Program of Shaanxi (No. 2020PT-021).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.