Main findings

In this study, we found that 44.8% of adolescents and young adults who died by suicide had at least one psychiatric diagnosis, whereas only 7.9% of the comparisons had psychiatric diagnoses. Overall, psychiatric disorders were attributable to 55.2% of the youth suicides. Major depressive disorder, dysthymia, and sleep disorder are the three major psychiatric disorders that contribute to youth suicides. In terms of subgroup analysis, we found that the PAF of overall psychiatric disorders for suicide among women (69.2%) was higher than that among men (45.5%). PAF among young adults (57.0%) was higher than that among adolescents (48.0%).

Our findings are in line with one cross-sectional study using coronial information in Australia, which reported that 40.9% of young people who died by suicide had a diagnosed mental disorder, and 15.7% had possible mental disorders (Hill et al., Reference Hill, Witt, Rajaram, McGorry and Robinson2021). A psychological autopsy study conducted in the United States showed that 59% of 120 subjects aged < 20 years who died by suicide had psychiatric diagnoses (Shaffer et al., Reference Shaffer, Gould, Fisher, Trautman, Moreau, Kleinman and Flory1996). Another study using the Demark Cause-of-Death Register and Psychiatric Center Register found that 38.7% of men and 57.1% of women aged ⩽ 35 years who died by suicide had a history of psychiatric admission (Qin, Reference Qin2011). Another case–control Australian study using coronial information for 84 youth suicides aged 18–34 years showed that the combined PAF for all psychiatric disorders was 48% in men and 52% in women (Page et al., Reference Page, Morrell, Hobbs, Carter, Dudley, Duflou and Taylor2014). All these studies demonstrate that the prevalence of psychiatric disorders among suicide cases is much higher than that of comparisons, suggesting that psychiatric disorders account for a substantial proportion of suicides.

The increasing trend in youth suicide is seen in Taiwan and many parts of the world, including the United Kingdom, the United States, Canada, and Australia (Chang et al., Reference Chang, Lin, Liao, Chen, Shaw, Hsu and Chang2022b; Padmanathan, Bould, Winstone, Moran, & Gunnell, Reference Padmanathan, Bould, Winstone, Moran and Gunnell2020). In Taiwan, elevated incident depressive disorders among adolescents and young adults (Wang et al., Reference Wang, Chang, Chang, Yang, Liu, Liao and Wu2022) might explain the increasing trend of youth suicide. Although the mental healthcare resource increased during the study periods (Wang et al., Reference Wang, Chang, Chang, Yang, Liu, Liao and Wu2022), the treatment rate was still low. We found that the prevalence of treated psychiatric disorders from this claims-based study was much lower than that of a nationwide survey, which showed the lifetime prevalence of psychiatric disorders among children and early adolescents was 31.6% (Chen et al., Reference Chen, Chen, Lin, Shen and Gau2020). In addition, income inequality, elevated parental divorce rates, increased prevalence of Internet use and poor sleep were also associated with the increasing suicide trends (Chang et al., Reference Chang, Lin, Liao, Chen, Shaw, Hsu and Chang2022b; Padmanathan et al., Reference Padmanathan, Bould, Winstone, Moran and Gunnell2020). The links between these social factors and suicide might be partially mediated by developing psychiatric disorders.

Depressive disorders and suicide

Depressive disorders, including major depressive disorder and dysthymia, contributed to the highest proportion of youth suicide in this study, mainly due to the high prevalence across sex and age groups. The underlying mechanism of the association between depression and suicide is complex, including the synergic effects of psychosocial stressors, genetics, monoaminergic neurotransmitters, and other neuromodulators (Orsolini et al., Reference Orsolini, Latini, Pompili, Serafini, Volpe, Vellante and Fraticelli2020). Many symptoms included in the diagnostic criteria of depressive disorders are associated with increased suicidal risks, including concentration deficit, poor sleep, low self-esteem, worthlessness, and negative inferential style (Burke et al., Reference Burke, Connolly, Hamilton, Stange, Abramson and Alloy2016; Nrugham, Larsson, & Sund, Reference Nrugham, Larsson and Sund2008). Anhedonia, also known as the inability to experience pleasure, is greater among adolescent suicide attempters than suicidal ideators or control (Auerbach, Millner, Stewart, & Esposito, Reference Auerbach, Millner, Stewart and Esposito2015), and is predictive of subsequent suicidal events (Yen et al., Reference Yen, Weinstock, Andover, Sheets, Selby and Spirito2013). Although the male gender is a risk factor for suicide among patients with depression; a recent meta-analysis study demonstrated that the suicidal risk of affective disorder was similar in both sexes (Li et al., Reference Li, Page, Martin and Taylor2011). In our study, the aORs of depressive disorders for suicide were similar between women and men. Given that the prevalence of depressive disorder was much higher among women than among men, the PAF of depressive disorder in women was 2-fold higher than that in men. Furthermore, we found the odds ratio of depressive disorder among adolescents was much higher than that among young adults. One Denmark study also showed that the incident rate ratios of depression for suicide were inversely associated with age (Qin, Reference Qin2011). These findings might partially explain the increased suicide risk of antidepressant treatment among the young population, especially adolescents (Esang & Ahmed, Reference Esang and Ahmed2018).

Schizophrenia and suicide

Patients with schizophrenia had the highest aOR among the overall study sample. In terms of subgroup analysis, we found that suicide risk among women was higher than that among men. One Demark study (Qin, Reference Qin2011) and one systematic review (Li et al., Reference Li, Page, Martin and Taylor2011) also demonstrated sex differences in the suicide risk associated with schizophrenia, with an increased risk for suicide in schizophrenia 10 times for males and 20 times for females. A possible explanation is that the symptom profile is different across sexes; men score higher in negative symptoms and disorganisation, and women have a higher prevalence of depressive symptoms (Morgan, Castle, & Jablensky, Reference Morgan, Castle and Jablensky2008). Depressive symptoms were the most important factor related to suicidality (Barbeito et al., Reference Barbeito, Vega, Sánchez-Gutiérrez, Becerra, Gonzalez-Pinto and Calvo2021). We also found that the suicide risk was higher among adolescents than young adults. A possible explanation is that suicide often occurs in the early course of schizophrenia, resulting in high suicide risk among adolescents (Moe et al., Reference Moe, Llamocca, Wastler, Steelesmith, Brock, Bridge and Fontanella2022).

Substance or alcohol use disorder and suicide

Substance or alcohol use disorder had the second-highest aOR for youth suicide. The association between suicide and substance or alcohol use disorder has been widely demonstrated (Esang & Ahmed, Reference Esang and Ahmed2018). Possible explanations include that substance or alcohol use would weaken impulse control and impair judgment, thereby increasing the risk of committing suicide (Albert, De Ronchi, Maina, & Pompili, Reference Albert, De Ronchi, Maina and Pompili2019). There was no overt sex difference in the association between substance or alcohol use disorders and suicide. We found that the risk of substance or alcohol use disorder for suicide is high among adolescents, which indicated that adolescents were vulnerable to substance and alcohol (Pompili et al., Reference Pompili, Serafini, Innamorati, Biondi, Siracusano, Di Giannantonio and Girardi2012). In addition, the legal alcohol drinking age ranges from 18 to 21 in most countries; thus, the prevalence of alcohol use disorder increased dramatically among young adults. Overall, the PAF of substance or alcohol use disorder among adolescents and young adults was similar.

Anxiety disorder and suicide

The suicide risk of anxiety disorder was relatively low compared to other psychiatric disorders, while its PAF was near 10%, owing to its high prevalence. The prevalence of anxiety disorder in women was almost twice that in men, which corresponds with a large Denmark population study of 21 169 suicides (Qin, Reference Qin2011). Previous studies have shown that anxiety disorder is associated with a higher risk of youth suicide (Page et al., Reference Page, Morrell, Hobbs, Carter, Dudley, Duflou and Taylor2014; Qin, Reference Qin2011), even after controlling for comorbid affective disorders and demographic characteristics. Possible explanations include difficulty maintaining interpersonal relationships when interpreting and coping with emotions.

Sleep disorder and suicide

Sleep disorders are prevalent in youth. It was the second most common psychiatric disorder in the comparison group and the third in the suicide group. Several studies have demonstrated that sleep disorders are associated with high suicidality among youth compared with that of other age groups (Liu et al., Reference Liu, Tu, Lai, Lee, Tsai, Chen and Chiu2019; Wong, Brower, & Craun, Reference Wong, Brower and Craun2016). Although sleep disorders might often be comorbid with other psychiatric disorders, it was a significant independent risk factor after controlling for covariates such as substance or alcohol use disorder or mood disorders (Goldstein, Bridge, & Brent, Reference Goldstein, Bridge and Brent2008; Liu et al., Reference Liu, Tu, Lai, Lee, Tsai, Chen and Chiu2019; Wong et al., Reference Wong, Brower and Craun2016). One possible explanation is that sleep disturbance worsens problem-solving abilities and increases impulsivity due to sleep deprivation and disrupted frontal lobe function (Goldstein et al., Reference Goldstein, Bridge and Brent2008; Perlis et al., Reference Perlis, Grandner, Chakravorty, Bernert, Brown and Thase2016). Another explanation is that sleep disturbance leads to low serotonin synthesis and postsynaptic serotonin receptor sensitisation in the prefrontal cortex (Liu et al., Reference Liu, Tu, Lai, Lee, Tsai, Chen and Chiu2019), finally resulting in poor judgment, increased impulsivity, and aggression.

Obsessive-compulsive disorder and suicide

Recent research had shown that OCD was significantly associated with suicidality, even after adjusting for socio-demographic variables and comorbidities (Albert et al., Reference Albert, De Ronchi, Maina and Pompili2019; Angelakis, Gooding, Tarrier, & Panagioti, Reference Angelakis, Gooding, Tarrier and Panagioti2015). However, there remained wide variation in prevalence and odds ratios between different studies (Albert et al., Reference Albert, De Ronchi, Maina and Pompili2019; Angelakis et al., Reference Angelakis, Gooding, Tarrier and Panagioti2015; Pellegrini et al., Reference Pellegrini, Maietti, Rucci, Casadei, Maina, Fineberg and Albert2020). It might be due to limitations, including high heterogeneity of study groups, high comorbidities with other psychiatric disorders, and different instruments used to assess suicidality (Pellegrini et al., Reference Pellegrini, Maietti, Rucci, Casadei, Maina, Fineberg and Albert2020). In addition, most studies were on suicidal ideation and attempts, except for two population-based studies from Sweden and Denmark, demonstrating that patients with OCD had an increased risk of suicide and unnatural death, respectively (Fernández de la Cruz et al., Reference Fernández de la Cruz, Rydell, Runeson, D'Onofrio, Brander, Rück and Mataix-Cols2017; Meier et al., Reference Meier, Mattheisen, Mors, Schendel, Mortensen and Plessen2016). In our study, only adolescents with OCD had a significantly increased risk of suicide. The association between OCD and suicide was not statistically significant among young adults. Whether there is an effect modification of age on the link between OCD and suicide needs future investigation.

Intellectual disability and suicide

The finding of reduced suicide risk in intellectual disability was consistent with studies in different nations. One retrospective cohort study from Denmark reported lower suicidal behaviours in intellectual disability (Erlangsen et al., Reference Erlangsen, Stenager, Conwell, Andersen, Hawton, Benros and Stenager2020). Another Finnish study demonstrated that men with intellectual disabilities have a lower suicide risk (Patja, Iivanainen, Raitasuo, & Lönnqvist, Reference Patja, Iivanainen, Raitasuo and Lönnqvist2001). People with intellectual disabilities might have limited skills in assessing high fatality suicide methods, thereby reducing suicide risk (Patja et al., Reference Patja, Iivanainen, Raitasuo and Lönnqvist2001). The severity of intellectual disability might also have a different influence on suicidality. Further research is needed to investigate the related mechanism or factors involved.

Psychiatric disorders with minor impact on suicide

Most psychiatric disorders were associated with a higher risk of youth suicide, except for tic disorders, autism, and acute stress disorder/post-traumatic stress disorder. The association between tic disorder and suicide was insignificant after controlling for other comorbid psychiatric disorders, indicating that tic disorders might not be an independent risk factor. The case number of acute stress disorder/post-traumatic stress disorder was relatively small, which might be because under-recognised in youth is common. Furthermore, ADHD and oppositional defiant disorder/conduct disorder were associated with an elevated risk of both OR and PAF in adolescents. The severity of these disorders generally subsided in adulthood; therefore, their association with suicide was not found in young adults. Notably, the prevalence of ADHD in our suicidal and non-suicidal groups was still much lower than those found in past Taiwanese epidemiological studies (Chen et al., Reference Chen, Chen, Lin, Shen and Gau2020). This result could be explained by the fact that ADHD is still underdiagnosed and undertreated in Taiwan. The impact of ADHD on suicide risk may have been underestimated in the present study.

Strengths and limitations

The strengths of this study are the use of the National Death Registry to identify all youth suicide and the comprehensive assessment of psychiatric disorders from the NHI outpatient and inpatient claims records. In addition, subgroup analyses were conducted to explore the modifying effects of age and sex. However, our study has several limitations. First, we assessed psychiatric diagnoses using the claims records. Individuals with psychiatric problems who did not seek help were not included. Previous epidemiological studies in Taiwan suggested that approximately 20–30% of individuals with depression sought medical treatment (Chang et al., Reference Chang, Liao, Chang, Wu, Huang, Hwang and Hsu2022a; Liao et al., Reference Liao, Chen, Lee, Lung, Lai, Liu and Chen2012). Therefore, the prevalence of psychiatric disorders has been underestimated. Generally, women are more likely to seek treatment than men; therefore, this might partly explain the sex difference in PAF of psychiatric disorders for suicide (Chang, Reference Chang2007; Miranda-Mendizabal et al., Reference Miranda-Mendizabal, Castellví, Parés-Badell, Alayo, Almenara, Alonso and Gili2019). In addition, individuals with lower incomes have more barriers to assessing mental healthcare services (Magaard, Seeralan, Schulz, & Brütt, Reference Magaard, Seeralan, Schulz and Brütt2017). Low income and other socioeconomic disadvantages were associated with poor mental health, such as a high risk of developing psychiatric disorders and high suicidality (Islam, Ormsby, Kabir, & Khanam, Reference Islam, Ormsby, Kabir and Khanam2021). Suicide group had significantly lower income than the comparison group; therefore, the odds ratios and PAF for suicide might be underestimated. Second, our database did not include several important confounding factors, such as childhood adversity, family support, family history of psychiatric disorders and suicide, and psychosocial stressors. Thus, the magnitude of the association between psychiatric disorders and suicide may be overestimated by not accounting for these factors. Third, we did not explore the odds ratio and PAF of specific psychiatric comorbidity for youth suicide because the possible combinations of psychiatric disorders are numerous, and the study sample size was limited. Therefore, we estimated the odds ratios and PAF of each psychiatric disorder for suicide with adjustment for other psychiatric disorders. The methods were consistent with previous studies (Chan et al., Reference Chan, Chiu, Chen, Chan, Wong D Psyc, Chan and Yip2009; Page et al., Reference Page, Morrell, Hobbs, Carter, Dudley, Duflou and Taylor2014). Fourth, we did not further distinguish early and late adolescents in subgroup analysis because the suicide number in early adolescence, aged between 10–14 years, was small (n = 62). Further investigations are needed to explore the role of psychiatric disorder on suicide among early adolescent. Finally, we calculated the PAFs of psychiatric disorders for suicide under the assumption that all psychiatric disorders could be treated completely. However, not all psychiatric disorders can be completely prevented or treated. Thus, the number of preventable cases may be lower than our estimates using PAFs.

Clinical implication

Our findings emphasise that early recognising and treating psychiatric disorders for youth suicide prevention, as more than half of youth suicide could be attributed to psychiatric disorders. School-based staff education and screening might help detect youth's psychiatric disorders and suicide risks early (Anderson et al., Reference Anderson, Ford, Soneson, Coon, Humphrey, Rogers and Howarth2019; Singer, Erbacher, & Rosen, Reference Singer, Erbacher and Rosen2019; Zalsman et al., Reference Zalsman, Hawton, Wasserman, van Heeringen, Arensman, Sarchiapone and Balazs2016). Evidence shows that psychotherapy and psychosocial intervention could treat psychiatric disorders and reduce suicide risk (Calear et al., Reference Calear, Christensen, Freeman, Fenton, Busby Grant, Van Spijker and Donker2016; Zalsman et al., Reference Zalsman, Hawton, Wasserman, van Heeringen, Arensman, Sarchiapone and Balazs2016). Although antidepressant agents effectively reduce depressive and anxiety symptoms, they were associated with increasing suicidality (Friedman & Leon, Reference Friedman and Leon2007) and should be used cautiously in the youth.

Public health resources are often limited, so focusing on disorders with higher PAF, including major depressive disorder, dysthymia, sleep disorder, and anxiety disorders, might be more efficient. Contrary to the common belief that men with schizophrenia had high suicidality, our study revealed that women with schizophrenia had higher suicide risks and required more assessment and management. Interestingly, sleep disorders are shown to have a significant role in youth suicide. This sheds light on the importance of evaluating sleep quality and quantity in youth. In primary care settings, youth with sleep disturbance should be assessed carefully, especially for the potential comorbid psychiatric conditions and suicide risk.

Although psychiatric disorders were the most important risk factor, other factors were still attributable to approximately half of the youth suicides. Restricting access to lethal means, establishing media guidelines for reporting suicide, gatekeeper training, follow-up contact for suicidal attempters, and other strategies should be combined to prevent youth suicide (Zalsman et al., Reference Zalsman, Hawton, Wasserman, van Heeringen, Arensman, Sarchiapone and Balazs2016).

Future research implication

As our data is generated from the NHI claims database, several important confounding factors are unavailable. Future studies should consider these factors, including childhood adversity, family support, and psychosocial stressors. In addition, a family history of suicide or psychiatric disorder could play an important role in youth suicide (Agerbo, Nordentoft, & Mortensen, Reference Agerbo, Nordentoft and Mortensen2002; Campos, Holden, Spínola, Marques, & Santos, Reference Campos, Holden, Spínola, Marques and Santos2020). Further investigations should address the impact of family history on the risk of youth suicide. Moreover, the treatment rate of psychiatric disorders in youth is still low. A proportion of non-diagnosed subjects who died by suicide may likely include those with undiscovered mental illness. Barriers to mental health service utilisation in youth should also be explored. Finally, the effectiveness of youth suicide prevention strategies is needed to be evaluated for the extent to which treatment can decrease youth suicide.