Main findings
Previous investigations have shown that there are various conditions associated with mental disorders. The distribution of the risk burden among adolescents and young adults across areas requires more study. Compared with the previous GBD study, which looked at the prevalence of mental illness across all age groups, we provide a more extensive and in-depth analysis of bipolar disorder among adolescents and young adults aged 10–24 years. To our knowledge, this is the first study to describe the prevalence and rate of change of bipolar disorder among adolescents and young adults aged 10–24 years in 204 countries at global, regional and national levels from 1990 to 2019.
The incidence of bipolar disorder in adolescents and young adults has increased every year since 1990. In 2019, those aged 15–19 years accounted for 669 188 (42.3%) of 1 582 095 cases among adolescents. Among adolescents and young adults, the group aged 15–19 takes up the largest proportion of bipolar disorder cases and presents the highest incidence. Globally, however, the greatest increase in incidence and YLDs was seen in the 20–24 age group (AAPC 0.42 (95% CI: 0.38 to 0.47)). This may be linked to global population growth.23 Especially from 2010 to 2019, the growth rate of incidence is greater than that of the previous two decades (AAPC 0.38 (95% CI: 0.33 to 0.43)).
Prevalence, incidence and YLDs of bipolar disorder did not differ significantly between males and females over the past 30 years. However, the overall prevalence, incidence and YLDs in females were slightly higher than those in males. In the past, many studies have discussed whether there is a gender difference in the prevalence and incidence of bipolar disorder. One ‘received wisdom’ is that there is no significant gender difference in bipolar disorder. Most studies also found almost equal sex ratios for 12 months and lifetime prevalence of bipolar disorder.24 However, studies have found that females are more likely to have rapid cycling, more mixed states, greater severity of acute episodes and a more severe course of illness than males.25 In addition, although the prevalence is comparable, females are more likely to receive specialist services for bipolar disorder,26 which may contribute to the higher prevalence of bipolar disorder in females because it is more likely to be diagnosed.
The incidence and burden of bipolar disorder among adolescents and young adults varies considerably by region and country according to the SDI. At the regional level, Australasia was the region with the highest incidence and YLDs of bipolar disorder (219.97 per 100 000 population (95% UI: 163.06 to 280.24) and 315.08 per 100 000 population (95% UI: 180.38 to 501.78), respectively), while East Asia was the region with the lowest incidence and YLDs (27.14 per 100 000 population (95% UI: 19.89 to 35.60) and 38.33 per 100 000 population (95% UI: 21.33 to 60.67), respectively) and the largest increase in incidence between 1990 and 2019 was observed in Southern Latin America (AAPC 0.17 (95% CI: 0.15 to 0.18)). This may be because Australasia provides the most complete data on the prevalence of common mental disorders.27
Bipolar disorder is the third leading cause of the burden of mental disorders among adolescents and young adults aged 15–24 years, and the burden has continued to grow since 1990 with no evidence of a reduction.2 Without intervention, this burden is likely to keep increasing. Specifically, inadequate global mental capital and unmet treatment needs among many adolescents with bipolar disorder may worsen this burden.28 The current low global median spending on mental health (US$2.50 per person annually, less than 2% of total health spending) may be a major reason for the large gap between young people’s mental health needs and the availability of preventive interventions.28 Some northern European countries have seen decreasing disease burden over the past 30 years, but the burden remains high in most countries across Europe. Although there are more financial investments and evidence-based interventions in high-income Europe than in other regions, services still fall far short of adolescents’ vast needs.29 Southern Latin America, experiencing the fastest growth in YLD over the past three decades and comprising more low-income and middle-income countries, has even less mental health capital to cope with the growing burden.28 30 Resources for preventing adolescent bipolar disorder and promoting mental health are unequally distributed around the world, and access to mental health services is severely inadequate for adolescents, especially in low-income and middle-income countries. Therefore, greater investments and initiatives to stem the rising burden are urgently needed.
The trend of increasing incidence of AAPC was observed in all five differing levels of SDI areas during the three decades. Middle SDI countries had the largest increase in incidence among adolescents and young adults (AAPC 0.41 (95% CI: 0.38 to 0.43)). Although growing at a slower rate, the high SDI and low SDI countries had a considerable number of original morbidity cases, far exceeding the other countries. Middle SDI countries did not have high incidence rates, but over three decades of development, the highest growth rates were observed in these countries, most likely due to economic and social changes. Thus, mental illness is now the most critical health problem facing the young in both developing and developed countries.31
In many global mental health studies, an intriguing observation emerges: high-income countries tend to exhibit higher prevalence rates of mental disorders (similar to the results of this study), although this seems perverse.32 33 A high proportion of individuals residing in less developed or low-income countries are at risk of mental disorders due to extreme stress caused by poverty, violence and disasters. Conversely, in developed countries, most individuals are shielded from these adversities. Why do high-income or developed countries exhibit a higher prevalence of mental disorders? One explanation is based on the ‘hedonic treadmill’ theory, in which people’s expectations rise in parallel with their wealth, which can lead to stagnation of happiness and even depression.32 34Simultaneously, some scholars combine this theory and infer that societal context moderates the pathogenic effect of stressors.33 35 For example, the same traumatic event, such as a car accident, may cause less psychological trauma to individuals after it occurs in a war-torn country than in a developed country.
Furthermore, social inequality may play a prominent role in the high prevalence in developed countries. This contribution may be particularly pronounced among those who are least likely to experience the socioeconomic advantages enjoyed by their wealthier compatriots in developed countries.32 This subgroup could be more susceptible to psychological trauma, especially based on the ‘hedonism treadmill’ theory, where the gap between the expectations and the actual wealth may be even more pronounced among these marginalised groups in developed countries.
As the results demonstrate, the burden of bipolar disorder disease has been increasing among adolescents and young adults. Adolescents with bipolar disorder suffer long-term effects such as an increase in unpleasant life events and a resulting decline in quality of life.36 In the psychological aspect, these age groups with bipolar disorder typically have poorer self-esteem, more hopelessness, more traumatic life events and more trouble controlling their emotions in situations that can make them angry.37
With the transformation of the job market, the use of high technology means that education is very significant. Several adolescents and young people have interrupted their education or work as a result of their diseases. A family and society invest a great deal of time and money in the development of an adolescent. If an adolescent has bipolar disorder during adolescence, there is not only a loss of upfront investment but also a loss of potential for future realisation, resulting in a loss of productivity. Despite the obvious and significant economic costs of mental illness, sufficient funding for this field has been woefully underfunded globally, particularly in non‐WEIRD (western, educated, industrialized, rich and democratic) countries.10 This situation results from several causes, including the prevalence of infectious diseases, widespread poverty, a lack of political stability and will, and inadequate infrastructure.10
The enormous burden of mental health disorders has reminded many leaders and researchers that despite the actions that have been taken, measures may be inefficient in terms of outcomes.38 First, adolescence is a very unique time, which dictates that alleviating their disease burden must consider some of the adolescents’ individual conditions. Psychopharmacotherapy, in conjunction with psychosocial therapies, is advised for treating bipolar disorder in adolescents.39 Second, adolescents may choose not to seek health services because of stigma and embarrassment, poor mental health knowledge and a preference for self-reliance.40 Destigmatisation is, therefore, also an important means of improving mental health. In addition, it is also vital to raise the health awareness of caregivers because their perceptions of mental illness stigmatisation can also affect mental health service utilisation and health expenditures.41
Last but not least, mental health services in the regions need to undergo transformational reforms to better meet the needs of young people.31 At the same time, interventions should focus not only on students within the education system but also on those outside the education system. However, the insufficient number of psychiatric professionals may also be a significant factor leading to the current unmet need for services for adolescents and young adults with bipolar disorder.42 This, therefore, requires that we design different services and interventions for bipolar disorder that consider different regional contexts and the different needs of adolescents and young adults, as well as scaling up mental health funding.
