Introduction

Suicide represents a critical global health threat, and since 2003, Korea has reported one of the highest suicide rates among OECD countries1. Globally, an individual dies from suicide every 40 s, highlighting the importance of identifying risk factors to prevent it2. Although suicidal ideation and depression are primary factors that directly lead to suicide attempts, many other demographic and physical activity factors also affect suicide rates3.

Various factors are associated with suicidal thoughts. In the general population, suicidal ideation is linked to depression, anger, a family history of psychiatric illness, and sleep duration4. Data from the national population of Denmark reveal that the risk of suicide substantially increases when the onset of physical and psychiatric illnesses occurs simultaneously5. The authors emphasize that physical illness is a crucial risk factor in suicide prevention, and this risk is further elevated when physical illnesses are accompanied by mental illnesses.

As aging societies have emerged as notable physical, mental, and socioeconomic health issues globally, including Korea, sarcopenia has gained considerable attention as a major mediator. Sarcopenia, characterized by decreased muscle mass and strength, along with reduced physical performance with aging, is closely associated with cardiometabolic diseases, frailty, falls, physical disability, hospitalization, and mortality6. Recently, sarcopenia has been reported to affect various mental illnesses, including depression7. However, although these data support a link between sarcopenia and suicidal ideation, research on this topic remains limited.

In this study, we analyzed nationwide, population-based survey data to examine the association between low muscle mass and suicidal ideation and to identify the factors that affect this association.

Results

Characteristics of participants

Of the 17,615 individuals, 2,902 (16.5%) considered suicide in the past year (suicidal ideation group). Table 1 summarizes the baseline characteristics of the participants in total and by sex. Household income level was significantly lower in the suicidal ideation group than in the non-suicidal ideation group (p < 0.001), a trend that persisted when assessed separately in males and females (both P < 0.001). Education level was also lower in the suicidal ideation group than in the non-suicidal ideation group, both overall and for each sex (all p < 0.001), whereas marital status showed no difference between the two groups. Participants who felt depressed were much more frequent in the suicidal ideation group, regardless of sex (both p < 0.001). A higher rate of low muscle mass was observed in the suicidal ideation group (10.8%) than in the non-suicidal ideation group (7.8%; p < 0.001). A significantly higher rate of low muscle mass in the suicidal ideation group was observed in females (P < 0.001), whereas no significant difference was found in males (p = 0.078).

Table 1 Baseline characteristics of the study participants.
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Impact of low muscle mass on suicidal ideation

Table 2 presents the effects of low muscle mass on suicidal ideation according to sex. Overall, after full adjustment by model 3, participants with low muscle mass exhibit significantly higher odds of suicidal ideation compared with those without, with an OR of 1.25 (95% CI: 1.02–1.52; p = 0.029). Specifically, in males, low muscle mass did not significantly affect suicidal ideation (OR, 1.14; 95% CI: 0.84–1.55; p = 0.384). However, in females, low muscle mass significantly increased the odds of suicidal ideation (OR, 1.31; 95% CI: 1.02–1.69; p = 0.036).

Table 2 Impact of low muscle mass on suicidal ideation.
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We also analyzed the effect of low muscle mass on suicidal ideation according to the age group (Fig. 1). Participants with low muscle mass between the ages of 50 and 79 years exhibited higher odds of suicidal ideation, with an OR of 1.33 (95% CI: 1.07–1.65; p = 0.009). However, for those aged < 50 or ≥ 80 years, the effect of low muscle mass on suicidal ideation was not significant.

Fig. 1
figure 1

Impact of low muscle mass on suicidal ideation by age group. Odds ratio is adjusted by sex, BMI, smoking, alcohol, exercise, DM, hypertension, household income, education level, marital status, depression, and stress level.

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Subgroup analysis

Figure 2 presents forest plots of the ORs for suicidal ideation in the sarcopenic group compared to the non-sarcopenic group based on prespecified subgroups established at baseline. These subgroups were categorized according to BMI (< 25 kg/m2 vs. ≥25 kg/m2), smoking (no vs. yes), alcohol intake (no vs. yes), regular exercise (no vs. yes), hypertension (no vs. yes), DM (no vs. yes), depression (no vs. yes), and stress levels (≥ moderate vs. ≤ low). The analysis revealed no differences across these subgroups, as indicated by the lack of statistically significant P-values for multiplicative interactions.

Fig. 2
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Subgroup analysis.

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Discussion

The current study demonstrated that suicidal ideation is substantially associated with low muscle mass, even after adjusting for various confounding factors such as depression and stress. These results were more pronounced in females and middle-aged individuals.

Suicide represents a crucial public health issue globally, accounting for more than 700,000 deaths annually8. Korea exhibits one of the highest suicide rates among OECD countries, prompting government actions to address this issue1. In the United States, the suicide rate among middle-aged adults has risen by more than 40% in the past 20 years, a contrast to the relatively stable suicide rates observed in other age groups9. Given the important roles played by middle-aged people in society, economy, and families, the rising suicide rate in this age group is a serious public health concern10.

The suicide process starts with suicidal ideation, progresses to suicide attempts, and ultimately culminates in suicide11. Therefore, it is important to identify and prevent the factors that induce suicidal thoughts at an early stage. Although the causes and mechanisms leading to suicide are not fully understood, they appear to involve various parameters. Depression is a notable risk factor for suicidal ideation as well as suicides. Kim et al. found that factors such as depression, lower quality of life, poor subjective health, or high stress were more probably to lead to suicidal ideation11. The authors concluded that suicidal thoughts are caused by multiple factors, not just one. Meanwhile, baseline depression may reduce physical activity and be an important risk factor for developing a sedentary lifestyle, which is linked to sarcopenia12. Our research showed that males with depression had lower skeletal muscle mass compared with those without depression, although this was not associated with central obesity13. A recent meta-analysis of 19 studies revealed an adjusted OR of 1.57 (95% CI: 1.32–1.86) between sarcopenia and depression7suggesting that depression may be a crucial link between sarcopenia and suicidal thoughts. In our study, the association between low muscle mass and suicidal ideation persisted, even after adjusting for depression.

Skeletal muscle substantially modulates systemic energy metabolism and communicates with other organs such as the liver, adipose tissue, and brain through the secretion of myokines. Myokines, which are cytokines or peptides released by muscle fibers, may mediate the beneficial effects of muscular exercise through autocrine, paracrine, or endocrine pathways14. Brain-derived neurotrophic factor (BDNF), a myokine/neurotrophin, plays a role in neural plasticity, neurogenesis, and synaptic transmission, affecting memory consolidation and cognitive function15. Kim et al. reported that BDNF concentrations were considerably lower in suicidal depressed patients than in non-suicidal depressed patients or controls16. Furthermore, Dwivedi et al. demonstrated a decrease in BDNF expression in the post-mortem brains of those who had committed suicide17. Recently, we found an association between BDNF levels and frailty in community-dwelling older adults using nationwide multicenter research data18. Both acute and regular exercise regulate skeletal muscle and circulating BDNF in sedentary older individuals19. Given the close relationship between sarcopenia and exercise, these data suggest that sarcopenia or exercise may affect suicidal thoughts and attempts by acting on the brain via myokines. Therefore, exercise has been suggested as a non-pharmacological intervention for sarcopenia and mental health. In fact, Ko et al. reported that regular walking exercise considerably lowered the OR for suicidal ideation and depressed mood in middle-aged adults20. Interestingly, the subgroup analysis of this study demonstrated that regular exercise did not show significant interaction on the results of this study, and prospective studies using exercise intervention are requested in the future.

Chronic low-grade inflammation, often referred to as inflammaging, is a key characteristic of ageing. This prolonged stimulation of the immune system can lead to sarcopenia21. Previous cross-sectional and longitudinal studies have shown that decreases in muscle mass and strength correlate with higher levels of proinflammatory cytokines, such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and C-reactive protein (CRP)21. Interestingly, researchers have observed increased IL-6 levels in the cerebrospinal fluid (CSF) of individuals who recently attempted suicide, and a relationship between IL-6 levels and the severity of depression22. Accumulated evidence supports the role of a dysregulated immune system in the pathophysiology of suicidal behavior22. Inflammation may affect suicide through altered effectors, including the hypothalamus-pituitary-adrenal (HPA) axis, the kynurenine pathway, and monoamine metabolism22. However, obesity and diabetes, which are representative disorders associated with chronic low-grade inflammation, did not show significant interaction in our subgroup analysis, so additional research through measurement of inflammatory markers is thought to be necessary.

Chronic diseases and physical disabilities are notable factors linking sarcopenia and suicidal ideation. A study of Koreans revealed that the number of chronic diseases was substantially associated with depression and suicidal thoughts in both males and females23. Sarcopenia and frailty, which lead to poor physical performance, disability, and chronic diseases, are critical concerns. Previous research, including our own, has shown the association of sarcopenia with diabetes and metabolic syndrome24,25. A meta-analysis found that diabetes notably increased the risk of suicide (relative risk (RR), 1.56; 95% CI: 1.29–1.89)26. A study using data from community-dwelling older adults found that physical frailty, such as lower gait speed and muscle weakness, was substantially associated with suicidal ideation, regardless of depression severity27. In our study, even after adjusting for confounding variables such as diabetes and hypertension, a remarkable relationship persisted between low muscle mass and suicidal ideation.

Age and sex are notable factors associated with suicidal ideation. A previous study reported a higher suicide risk in older males28. A sharp increase in suicide rates among the population aged 45–54 in 2015, at 32.1 per 100,000, contributing to the overall increase in suicides in Korea10. The suicide rate among Korean females decreased after 2011, but is now increasing again29. In this study, the association between sarcopenia and suicidal ideation was not clearly shown in the younger group (< 50 years old) or the older group (≥ 80 years old). It is difficult to determine the exact cause based on this study alone, but the younger group had not yet fully developed sarcopenia, and the older group with severe sarcopenia or clear suicidal ideation may have died early, which may have affected the results. Interestingly, pre-menopausal and post-menopausal females exhibit distinct factors influencing suicidal ideation, beyond common elements such as experiences of violence, stress, and depression30. For pre-menopausal females, religious beliefs, alcohol use, and chronic diseases are significant individual-level factors, whereas for post-menopausal females, perceived health status plays a crucial role. The current study supports a robust relationship between muscle loss and suicidal ideation, particularly in females and middle-aged individuals. Midlife is a life-period of high stress by facing both high familial and social expectations yet decreasing physical health31,32 leading to a rise in midlife suicide worldwide33,34. Moreover, middle-aged women go through the menopause transition in this period which makes them physically and mentally unstable driven by hormonal dysregulation and makes them vulnerable to suicide35,36,37. A recent study in Koreans reported that sarcopenia was more strongly associated with metabolic syndrome in women than in men38 and individuals with metabolic syndrome are more likely to have suicidal ideation39. A Swedish cohort study, which included more than one million participants, found that higher muscular strength in adolescence was associated with a 20–30% lower risk of death from suicide over a median follow-up of 24 years40. These findings highlight the importance of personalized interventions based on age, sex, and psychosocial and physical issues for suicide prevention.

This study has several limitations. First, this was a cross-sectional study; therefore, a causal relationship could not be established. Whether individuals with suicidal ideation have reduced physical activity, poor nutrition, or other behaviors leading to muscle loss could not be concluded from this study. In cross-sectional studies such as this one, the reverse causality hypothesis has important implication that should be considered. In a meta-analysis including 21 studies, higher physical activity levels were associated with lower suicidal ideation, but this needs to be confirmed in prospective or controlled trials41. Second, it included only Korean males and females, which means that the results cannot be generalized to populations of different ethnicities. Further research involving diverse races and populations is required. Third, despite extensive adjustment for potential confounding factors, we could not eliminate any residual effects. Fourth, subgroup analyses across BMI, lifestyle, and comorbidity showed the null interaction, which may be related to reduced statistical power due to limited sample size or measurement constraints. Future studies using larger or more strategically designed samples are needed to investigate these interactions. Finally, although muscle mass is a crucial element of sarcopenia, the absence of data on muscle strength and physical performance in this database calls for additional studies incorporating these components. However, this study also has notable strengths. It uses government-led, nationally representative data from Korea, and demonstrates a significant association between muscle mass and suicidal ideation in the general population, reflecting a real-world situation. The validity of the database is supported by its large sample size, standardized data collection by trained interviewers, and calibration with a wide range of associated variables. In a broad range of subgroup analyses, we observed consistent results, without significant interactions.

In conclusion, this study demonstrated a substantial association between skeletal muscle loss and suicidal ideation, and this result persisted even after extensive adjustments for confounding factors such as anthropometric, socioeconomic, physical, and psychological parameters. The recent increase in the threat of suicide and sarcopenia highlights the importance of screening for sarcopenia and implementing intervention efforts to reduce the risk of suicide in individuals diagnosed with sarcopenia, particularly middle-aged females.

Methods

Study population

This study used data from the Korea National Health and Nutrition Examination Survey (KNHANES) conducted from 2008 to 2011, during which participants underwent dual-energy X-ray absorptiometry (DXA). KNHANES is a nationwide cross-sectional survey performed by the Korea Centers for Disease Control and Prevention to provide national health, diet, and nutrition data representing non-institutionalized citizens residing in South Korea. Participants were selected using a two-stage stratified cluster sampling approach based on population and housing census data. Detailed information was collected through household interviews conducted by well-trained staff and standardized physical examinations. Each participant provided written informed consent before the survey, and secondary anonymized data were used for the analyses. The institutional review board of the Korea Centers for Disease Control and Prevention approved the protocol of the KNHANES (IRB approval number: 2008-04EXP-01-C, 2009-01CON-03–2 C, 2010-02CON-21-C, and 2011-02CON-06-C). Detailed information about the survey, sampling procedures, and the anonymized KNHANES database is publicly available at https://knhanes.kdca.go.kr/knhanes/eng/index.do.

Of the 37,753 participants in the KNHANES 2008–2011, we excluded those who lacked data on DXA (n = 16,914) or had incomplete information on suicidal ideation or baseline characteristics (n = 3,224). The final analysis included 17,615 participants, as shown in Fig. 3.

Fig. 3
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Flow chart.

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The study protocol was approved by the Institutional Review Board of Korea University (IRB number 2024GR0445) and was performed in accordance with relevant guidelines/regulations and the Declaration of Helsinki.

Mental health

The mental health section of KNHANES was used to assess suicidal ideation, depression, and stress. Participants who answered “yes” to the question, “Have you seriously considered suicide in the past year?” were categorized into the suicidal ideation group. Those who responded “yes” to “Have you had feelings of sadness or hopelessness that interfered with your daily life for over two consecutive weeks in the past year?” was classified as depressed. The degree of stress was categorized as high, moderate, low, and near none, based on responses to the question “How much do you feel stressed out in daily life?”

Appendicular skeletal muscle mass

Appendicular skeletal muscle mass (ASM), which represents the total lean mass of both the right and left arms and legs, was measured using DXA (QDR Discovery; Hologic, Inc., Bedford, MA, USA). Low muscle mass was defined according to the Foundation for the National Institutes of Health criteria, calculated as ASM divided by body mass index (BMI), with cutoff points of ≤ 0.789 in males and ≤ 0.512 in females.

Covariates

Baseline characteristics were categorized into age (< 50, 50–79, or ≥ 80 years), household income (low, middle-low, middle-high, or high), educational level (less than elementary school, middle school, high school, or college or higher), and marital status (married or single). Diabetes mellitus (DM) is defined as fasting blood glucose levels ≥ 126 mg/dL, use of antidiabetic medication, or a physician’s diagnosis of DM. Hypertension was defined as the use of antihypertensive medication or a physician’s diagnosis.

Statistical analysis

Data analysis was performed using R version 3.4.0 (R Foundation for Statistical Computing, Vienna, Austria; available at http://www.R-project.org). All statistical analyses were conducted using the sample weights assigned to the participants in the KNHANES to achieve unbiased estimates that represent the entire South Korean population. Continuous variables are presented as medians with interquartile ranges (IQRs) and were compared using Kruskal-Wallis tests. Categorical variables are shown as frequencies with weighted percentages and were compared using the chi-square test. We analyzed the association between low muscle mass and suicidal ideation using multivariable logistic regression models, adjusting for potential confounding factors such as age, sex, BMI, smoking, alcohol intake, exercise, DM, hypertension, household income, education level, marital status, depression, and stress level.