Main findings

Using data from GBD 2019, we investigated the association between sociodemographic development and the burden of mental disorders, substance use disorders and self-harm across four age groups (10–24, 24–49, 50–69 and ≥70 years) from 1990 to 2019. Although the burden of poor mental health remained fairly constant from 1990 to 2019, except in the case of self-harm, differential changes in the burden of poor mental health by sociodemographic development were observed across age groups. DALY rates for mental disorders, substance use disorders and self-harm were significantly correlated with sociodemographic development, although these associations were heterogeneous across age groups. Higher SDI at the country level was accompanied by higher DALY rates for poor mental health, particularly depressive disorder and substance use disorder among younger individuals. However, the opposite association was found among older age groups (e.g. ≥70 years), where increased sociodemographic development was associated with a decreased or less-increased disease burden. Furthermore, the association of sociodemographic development with the burden of poor mental health changed differentially across age groups. The burden of mental disorders and substance use disorders remained concentrated in countries with high SDI index scores, especially for youth and young adult groups.

Interpretation of findings

For three decades, regions with high SDI have had higher DALY rates for mental and substance use disorders than low SDI regions among younger age groups, although they had lower DALY rates among older groups. In line with our findings, previous studies^{Reference Castaldelli-Maia and Bhugra19,Reference Dückers, Reifels, De Beurs and Brewin21,Reference Dückers, Alisic and Brewin35,Reference Heim, Wegmann and Maercker38} have found that the disease burden of mental disorders, substance use disorders and self-harm is paradoxically greater in less vulnerable or more developed areas. This has been referred to as the ‘vulnerability paradox’^{Reference Dückers, Reifels, De Beurs and Brewin21,Reference Dückers, Alisic and Brewin35,Reference Dückers, Witteveen, Bisson and Olff36} and indicates a counterintuitive association between mental health and socioeconomic resources at the country level.^{Reference Dückers, Reifels, De Beurs and Brewin21} Specifically, our findings highlight that the vulnerability paradox is stronger among youth and young adults than older adults. People who experience mental disorders have lower subjective well-being,^{Reference Jorm and Ryan22} and previous studies have shown that children and adolescents in wealthier nations have lower subjective well-being,^{Reference Rudolf and Bethmann24,Reference Bălțătescu and Michalos39} whereas the adult population has higher subjective well-being compared with their counterparts in less developed countries, consistent with our findings. Although reasons may be multifactorial and related to individual-level factors, we posit that a key explanation for differential trends and patterns of sociodemographic disparities in the burden of poor mental health across age groups is a complex interplay of two major country-level factors: differences in economic and cultural backgrounds and mental health systems.

In most high SDI countries, highly developed or productive societies may have established social values, cultural traditions, and social networks^{Reference Adebisi40} that improve their monetary value of pleasure.^{Reference Barbalat and Liu20} Generally, these societies might be characterised by higher levels of competitive individualism and indulgence, with less satisfaction obtained by pursuing basic desires. These sociocultural factors may lead to increasing pressure to achieve success and sensitivity to social failure.^{Reference Dückers, Reifels, De Beurs and Brewin21} Accordingly, a systematic review found that economic crises such as recessions are associated with a risk of suicide, particularly in high-income countries.^{Reference Oyesanya, Lopez-Morinigo and Dutta41} Moreover, we observed that DALY rates for mental disorders, particularly depressive disorder, in younger groups were increasingly concentrated in countries with high SDI levels, in contrast to trends observed in older age groups. Previous studies have found that social relationships and material circumstances, such as standard of living, are highly associated with subjective well-being in adult groups, whereas perceived life satisfaction with freedom is a factor significantly associated with subjective well-being in youth.^{Reference Bradshaw and Rees42} Notably, in countries and societies whose sociocultural environments force tougher restrictions on sustained enjoyment of life than before, youth and young adults are more likely to have limited freedom and control over their lives because they are governed by social norms and their parents.^{Reference Minkov43} In particular, educational policies intended to improve school productivity among youth or college students result in increased intensity of learning and working.^{Reference Rudolf and Bethmann24} Higher learning and work intensities may be linked to national socioeconomic development and educational achievement. However, these factors could also adversely affect people's mental health in various ways, such as decreased well-being or increased cognitive overload.^{Reference Rudolf and Bethmann24,Reference Bălțătescu and Michalos39} Restriction of freedom and life control could be coupled to a low level of social support and integration because they are likely to be associated with autonomous activities such as using computers or mobile devices,^{Reference Rudolf and Bethmann24} including the rise in use of social media among young people. Previous research has suggested that internet use is more common in wealthy countries,^{Reference Poushter, Bishop and Chwe44} and social media use among young people has greatly increased, reaching higher levels in this group compared with other age groups.^{Reference Jackson, Janssen and Gabrielli45} Specifically, another study revealed that among 11 high-income countries, nearly all had experienced an increase in social media use; in some of the countries with the most significant increases, these were found to be associated with higher rates of youth suicide.^{Reference Padmanathan, Bould, Winstone, Moran and Gunnell46} Young people may be less likely to discuss emotional or personal problems or show help-seeking behaviour,^{Reference Dückers, Reifels, De Beurs and Brewin21,Reference Dückers, Alisic and Brewin35} which may lead to further deterioration of their mental health. Instead, they may turn to misuse of alcohol or drugs, which has an impact on the burden of substance use disorders. Our findings found that the increased burden of substance use disorders was highest among young people in high SDI countries. Previous studies have found that psychiatric disorders, particularly depressive disorder, coexist with substance use disorders owing to extreme alcohol or drug use and/or dependency.^{Reference McHugh and Weiss47,Reference Brook, Brook, Zhang, Cohen and Whiteman48} With recent advances in internet services, the availability of alcohol and drugs may have become higher owing to content and postings on social media.^{Reference Romer and Moreno49} Given the substantial increase in use of the internet and social media, as youth and young adults are the most active users,^{Reference Poushter, Bishop and Chwe44,Reference Jackson, Janssen and Gabrielli45,Reference Moreno and Whitehill50} they may be more susceptible to exposure to information on alcohol and drugs.^{Reference Jackson, Janssen and Gabrielli45} This exposure could potentially reduce negative perceptions of the consequences of alcohol and drug use and enhance normative perceptions,^{Reference Romer and Moreno49} which may lead to increased DALY for substance use disorders among young people, particularly in high SDI countries. Therefore, in recent years, within more competitive societies and education systems with higher material and social aspirations, these factors, including less interaction with family or friends and increased social medial use, could eventually lead to poorer mental health and explain how sociodemographic development could affect mental health among younger groups in countries with high levels of SDI. The youth mental health burden in high SDI countries is an emerging public health concern that should be addressed.

Although the DALY rates for mental health and substance use disorders were lower in lower SDI regions compared with high SDI regions, this should not lead to a belief that treatments for poor mental health conditions are priorities for only developed countries. A possible explanation is variations in mental health literacy and accessibility to professional psychiatry services among countries.^{Reference Dückers, Reifels, De Beurs and Brewin21,Reference Thornicroft, Chatterji, Evans-Lacko, Gruber, Sampson and Aguilar-Gaxiola51,Reference Saraceno, van Ommeren, Batniji, Cohen, Gureje and Mahoney52} These factors could influence recognition of mental distress and the probability of being diagnosed and treated for mental illness.^{Reference Renwick, Pedley, Johnson, Bell, Lovell and Bee53} They may also precipitate and perpetuate mental health symptoms if countries have low mental health literacy and low accessibility of professional psychiatry services.^{Reference Patel, Kieling, Maulik and Divan54} Compared with high SDI countries, where treatment uptake for poor mental health has increased since 1990,⁷ there has been a report of later onset or recognition and higher persistence of mental illness in low-income countries.^{Reference Ruscio, Hallion, Lim, Aguilar-Gaxiola, Al-Hamzawi and Alonso10} Although the supportive aspects of social capital, such as social support and community engagement, could substitute for low mental health literacy and availability of mental health services in less developed countries,^{Reference Dückers, Reifels, De Beurs and Brewin21,Reference Dückers, Witteveen, Bisson and Olff36} implementation of prevention and early diagnosis of mental illness is still essential for children and adolescents in low-income countries, because the youth population could buffer the long-term consequences of the mental health burden in those who need mental health treatments the most.⁷ Thus, there is a need to expand the delivery of effective prevention and treatment programmes with established efficacy to cover more of the population for the necessary duration in both high and low SDI countries.

Prevention and early intervention for mental health problems among youth and young adults are essential regardless of sociodemographic development to ensure a reduction in the mental health burden of young people and a socially and mentally healthy future adult population.

Methodological considerations

This study provides comprehensive information on global trends and patterns in the burden of poor mental health conditions by sociodemographic development across age groups from 1990 to 2019. However, it should also be noted that interpretation of our findings needs to be cautious, considering the following methodological considerations. First, this study was based on data from GBD 2019, in which the methodology of estimating the burden of mental disorders, substance use disorders and self-harm had limitations, as generally highlighted in previous studies.^{7,Reference Naghavi, Abajobir, Abbafati, Abbas, Abd-Allah and Abera26} Notably, there were variations in data quality among countries. Although estimates of GBD 2019 were calculated using a large amount of epidemiological survey data and rigorous statistical estimation methodology, estimates for some low- and middle-income countries may have been biased owing to sparsity of primary data.⁷ Cultural and religious ramifications such as social stigma may lead to underreporting of mental health problems. Although GBD 2019 used the DSM and ICD to ensure consistency in disease definitions across different epidemiological studies,⁷ these classifications might not reflect different cultural contexts in each country,^{Reference Marques, Robinaugh, LeBlanc and Hinton55,Reference Patel56} resulting in differential misclassification. Furthermore, the estimates from GBD 2019 were based solely on disease symptoms and did not take into account psychological indicators such as undiagnosed mental health symptoms or quality of life. Therefore, the cross-cultural applicability of criteria for mental-health-related case definitions and methodology for data collection need to be considered in further GBD studies.⁷ Besides, more high-quality epidemiological research from low- and middle-income countries with more standardised methods might be needed to address these limitations. Second, this study used aggregated country-level data, which may lead to ecological fallacy and should not be interpreted as findings at the individual level. Last, we investigated the associations of a broad spectrum of burden of poor mental health and sociodemographic development with mental health, but we could not clearly explain these relationships because other contextual factors, such as cultural and health-related factors affecting mental illness, could not be used for all countries throughout the study period owing to limited data. Thus, we were very cautious when drawing conclusions based on previous studies. However, it is necessary to better understand cross-national differences in mental health burden resulting from several other factors. Further research quantifying the contribution of other contextual factors would be meaningful for developing global and country-level mental health intervention strategies to reduce the burden of poor mental health.

Future implications

This study provides important insight into global and country-level mental health burdens across age groups by showing regional disparities in DALY rates of poor mental health, with higher SDI countries having higher DALY rates among younger groups and lower estimates among older groups than lower SDI countries. Based on our findings, three points deserve emphasis for future mental health policy and research. First, mental health strategies need to be considered within a broader sociocultural context to improve social well-being in high SDI countries. Second, in low SDI countries, mental health systems need to respond to the growing burden of poor mental health among the older population. These include improving early diagnosis and treatment for youth and reducing mental health stigma in a socially acceptable manner with further economic and social infrastructure developments. Last, more epidemiological studies should be conducted to advance our understanding of the global mental health gap and develop effective strategies in global and national contexts for decreasing disease burden.