Our study population comprised 4,675 suburban-dwelling older individuals (aged 60 years old and above) from the Chongming, Pujiang, Jiading and Hongkou Districts of Shanghai, China who were participated in China’s national free physical examination program between 2020 and 2023. The inclusion criteria for participants were age ≥60 years, willingness to participate in this study, and completion of the relevant information. Exclusion criteria were as follows: (1) those with incomplete depression data; (2) those with incomplete living arrangements information; (3) those unable to perform the bone density test. The final analytic data consisted of 4,240 participants (Figure 1).

This study was approved by the ethical committee of the Shanghai University of Medicine and Health Sciences, and all participants gave full, informed written consent to take part in the study.

Living arrangements were assessed by a questionnaire item: “How many people are in your household, except yourself?.” Participants were defined as living alone if they are the only member in the household. Those who reported any co-resident were classified as living with others (25, 26).

The bone mineral density (BMD) was measured at the distal one-third radius of the non-stressed forearm by the portable dual-energy X-ray absorptiometry (EXA-3000; OsteoSys, Co., Ltd., 901-914, 9F, Jnk Digitaltower, 111 Digital-ro 26, Guro-gu, Seoul 152-848, Republic of Korea), which was calibrated by trained technicians every day. Based on World Health Organization (WHO) criteria (27), a T score ≤ − 2.5 was considered to indicate osteoporosis.

Depressive symptoms were diagnosed by an interview using the Chinese version of Geriatric Depressive symptoms Scale (GDS). GDS is a standardized self-reported questionnaire comprising 30 dichotomous questions, with a total score ranging 0–30. And greater values indicate increased severity. Participants with a GDS score 11 or above were defined as those with depressive symptoms (28).

In this study, we controlled for the following variables as covariates: sociodemographic characteristics, behavioral characteristics, condition of chronic diseases.

Demographic characteristics, including age, gender, social contact, monthly income, and education level were assessed. Behavioral characteristics included smoking and drinking habits. Current smoking habits were grouped into 2 categories: current smoker, non-smoker. Current drinking habits were grouped into 2 categories: current drinker, non-drinker. Social contact was assessed with the following question: “Do you regularly interact with family or friends in daily life?.” Participants were divided into 3 categories: none, irregular, and regular. Education level was grouped into 2 categories: illiterate and non-illiterate.

We used the short form of the International Physical Activity Questionnaire (IPAQ) to assess physical activity (29). The nutrition status was measured using the Mini Nutritional Assessment (MNA) (30). The history of medical conditions such as diabetes, hypertension, hyperlipidemia and stroke was established according to his or her response (yes or no) to questions, the physician’s diagnosis and medication or treatment.

Participants were divided into four groups to determine combined conditions of living alone and osteoporosis status. Four groups, respectively, are living with others and non-osteoporosis; living with others and osteoporosis; living alone and non-osteoporosis and living alone and osteoporosis groups.

Continuous variables were presented as the mean ± standard deviation (SD), whereas data with a non-normal distribution were expressed as the median (25–75% interquartile range). Categorical variables were summarized as an absolute number and proportion (%). Comparisons among four different groups were examined using analysis of variance, Kruskal-Wallis rank tests and Chi-square tests. Furthermore, a binary logistic regression analyses were performed to examine the association of living alone or osteoporosis with depressive symptoms in older adults. Analyses were conducted in crude (Model 1 and Model 2) and adjusted (Model 3, Model 4, and Model 5) models. All statistical analyses were performed with SPSS V25 and p values less than 0.05 were considered statistically significant.

Of the 4,240 (mean age, 71.75 ± 5.88 years; 58.0% women) in the final analysis, 515 (12.1%) were assessed to have depressive symptoms (7.9% in males and 15.2% in females). Table 1 displays the characteristics between participants with and without depression. Depressed individuals were older, females, more likely to live alone, and had lower BMI, lower MNA score and a higher prevalence of osteoporosis. Table 2 categorizes participants by living alone and osteoporosis status. Compared to the other three groups, participants in the living alone and osteoporosis group were older, predominantly female, had lower IPAQ scores, more often illiterate, and exhibited the highest frequency of depressive symptoms.

As shown in Figure 2, the prevalence of depression was highest in the living alone and osteoporosis group and lowest in the living with others and non-osteoporosis group; this pattern was consistent across both sexes.

The analyses were performed separately for males and females due to the known gender differences in depression (20). Tables 3, 4, respectively, showed the logistic regression analyses for living alone and osteoporosis with depression by gender. We found that living alone was significantly associated with depressive symptoms for the males and females in model 1 (all p < 0.05). Model 2 in females showed that osteoporosis was significantly associated with depressive symptoms (p < 0.001). After adjusting for potential confounders (age, BMI, IPAQ, MNA score, social contact, monthly income, education level, current smoking, current drinking, diabetes, hypertension, stroke), we observed that living alone (OR = 2.03, 95%CI = 1.20–3.41 in males; OR = 1.86, 95%CI = 1.37–2.54 in females) was significantly correlated with depressive symptoms. However, we did not find any statistically significant differences between osteoporosis and depressive symptoms both for males and females in model 4. Compared with the living with others and non-osteoporosis group, we found that only the living alone and osteoporosis group showed statistically significant association after adjusting for potential confounders in males (p < 0.001). However, in females, participants living alone, regardless of osteoporosis status, had greater adjusted risks of depression (all p < 0.05).

Our study found that after adjusting for potential confounders, osteoporosis had no association with depression both in males and females. This result was in accordance with a previous study (21). But some studies revealed contradictory results (15, 23). A cross-sectional study in Iran used the Persian version of the 13-item Beck Depression Inventory (BDI) (23), whereas the USA sample aged ≥50 years used the Patient Health Questionnaire-9 (PHQ-9) (15); both reported an association between osteoporosis and elevated depressive symptoms.

By contrast, our GDS-based research of Chinese community-dwelling older adults (≥60 years) did not show a significant association. The contradiction may result from the difference in the population characteristics; behavioral habits and the different assessment instruments used in the research. People with osteoporosis in our study were less likely to drink, while the Iranian population showed the opposite pattern (23). It is hoped that more future research will investigate the relationship between osteoporosis and depression.

Our study revealed a significant association between living alone and depressive symptoms in both sexes, which persisted after adjusting for confounding factors and was consistent with the previous studies (7, 9). The observed association between living alone and depressive symptoms may be partly explained by the absence of social and economic support from family members or friends, a factor previously linked to higher levels of depression (6). Mutual support and a sense of belonging are highly valued, especially in Chinese culture (11, 31). Consequently, Chinese older individuals living alone are more prone to feeling neglected, leading to unhealthy psychological outcomes (31). Moreover, we found that participants living alone tended to have fewer health-promoting behaviors and worse nutritional status (13). One possible explanation was the lack of support and guidance from friends and family, which influence physiology and psychological well-being (9, 32). Surprisingly, in our study, people who lived alone had lower smoking rates, a finding that appeared counter-intuitive but could reflected fewer social cues to smoke. So, further studies considering additional details of living alone need to be conducted in the future.

Our study suggested that the relationships between living alone, osteoporosis and depressive symptoms were different for females and males. However, what remains consistent is that the combination of living alone and osteoporosis was related to higher levels of depressive symptoms (20).

Surprisingly, osteoporosis was more strongly associated with elevated depressive symptoms in the male subjects living alone (OR = 3.61, p < 0.001) than female participants (OR = 2.21, p < 0.001). Due to the traditional gender roles, males might have less time to do the housework, and they might be more dependent on females for personal lives and social care, especially in East Asian countries such as China (33, 34). So, even living alone, males are more likely to adopt sedentary lifestyles and participate in less physical activity, especially those with osteoporosis, which increased greatly the ill effects of living alone on depression.

Living alone was associated with various adverse health outcomes—such as decreased physical activity, frailty, falls and higher all-cause mortality—and were also linked to an increased risk of osteoporosis (13, 35). In addition, engaging in outdoor physical activities can help individuals living alone maintain bone mass and reduce the risk of depression (7, 13, 19), partly because physical exercise may increase endocannabinoid concentrations that could ease symptoms of anxiety and depression (36). However, evidence has shown that these individuals are less likely to engage in physical activity and experience a profound decline in activity levels over a two-year follow-up (37). Therefore, maintaining a healthy lifestyle is very important for people living alone to protect bone and mental health.

We also found that living alone was independently associated with more severe depressive symptoms among women. This might be because women are more prone to stress than men (38). Once distressed, females tended to exhibit more anxiety and depression than males when experiencing stress (39). In males, neither living alone nor osteoporosis was significantly associated with depression; rather, the risk elevated only when both conditions were present (OR = 3.61). A possible explanation is the sex differences of stress exposure and stress susceptibility: women frequently develop depression after isolated social stress while men require multiple physical and social stressors (40, 41). On the other hand, older men living alone often enjoy solitude and are more inclined to engage in activities to achieve self-satisfaction and personal growth (42).

Moreover, we observed a pronounced link between socioeconomic inequalities and health. Among men, higher monthly household income attenuated the adverse effects of living alone and osteoporosis on the development of depressive symptoms. Among women, more frequent social participation exerted a stronger protective effect. We speculate that the observed association stems from the fact that adult children are the main source of most Chinese older people from a cultural perspective (31). However, financial independence enables older population to live independently and gain more privacy and autonomy because living alone is not perceived as stressful (9, 10, 39). Active social interactions have shown to improve health promotion and successful aging (43, 44), especially among females, who typically have more extensive social networks than males (31). So, our study suggested that it is necessary to take active aging interventions to help improve the life quality of the older people living alone and ensure their well-being.

The existing research on the separate and combined effects of living alone and osteoporosis on depression is limited. Our study supplemented this information in the Chinese community-dwelling older population. And these findings may provide new insights for clinical care. However, this study had several limitations. Firstly, as this was a cross-sectional study, the causal relationship cannot be determined. Secondly, the participants of this study were almost relatively healthy ones who were able to engage in the annual national physical examination. Thus, our sample may not be comprehensive and representative enough for other regions. Thirdly, we did not consider what effect the transition of living arrangements may have. In the future, further longitudinal follow-up studies are required.