Natália GregoriniPsychiatric disturbances can manifest as early in life as from infancy, although they become more frequent during teenage years and in early adult life, when they can cause more economic and social impact. Based on data from 159 countries collated between 1990 and 2019, an international group of researchers led by Brazilian psychiatrist Christian Kieling, of the Federal University of Rio Grande do Sul (UFRGS), estimated the proportion of people around the globe who potentially presented at least one mental disorder in the early phases of life from 5 to 24 years—the period in which cases tend to occur more due to age.
The overall numbers are notable for their magnitude, although they do not surprise the specialists. In 2019, a total of 293 million people in this age group presented symptoms compatible with some of the 11 psychiatric disorders evaluated; from the most common anxiety and depression, to the rarer, such as dietary disorders or schizophrenia. Presented in an article published at the end of January in the medical journal JAMA Psychiatry, this number corresponds to 11.6% of the global population between 5 and 24 years, which at the time was 2.52 billion individuals.
Previous studies have already calculated the prevalence of these issues in childhood and youth. Generally, however, they were based on slightly more advanced ages, from 10 or 12 years, and included a shorter extension, to the end of the teenage years. According to Kieling, this sample could distort the numbers by not including the years in which such disorders start to manifest or are diagnosed, when the frequency is naturally lower—a previous evaluation of the 10–19 age group estimated the frequency of psychiatric issues at 13.1%. On addressing this interval as unique, other studies did not look at what the specialists call the journey of disorders, i.e., how their prevalence changes with age.
To obtain more comprehensive information Kieling and his collaborators, including researchers from São Paulo, Canada, and the US, decided to add people from a wider age range (mid-childhood to early adult life) and analyze the data for narrower age groups, in order up to gauge both the global and individual pathway of these disorders. “What concerned me was the lack of a more granular view of shorter age intervals in childhood and teenage years, when all the changes in organisms and social interactions happen a lot faster,” says Kieling.
The data obtained under the new strategy indicate that the overall prevalence of these issues varies significantly, primarily between childhood and the beginning of adolescence. From 5 to 9 years of age, 6.8% of children had at least one psychiatric disorder, with the number almost doubling to 12.4% between 10 and 14 years, and arriving close to 14% in the ranges 15–19 and 20–24, remaining stable in subsequent years. “We ran the calculations for older age groups, and saw that the frequency plateaus out,” reports the UFRGS researcher.
According to the study authors, this increase in prevalence has made it very clear that childhood and adolescence are a crucial period for interventions aimed at preventing the development of psychiatric disorders or, once they manifest, at reducing their gravity and impact on life, and stopping them from becoming chronic. After all, the incidence of psychiatric disorders does not increase so quickly in any other phase of life. A study of a thousand people from birth to 26 years of age in New Zealand had already shown that 74% of those with psychiatric issues had been diagnosed before they were 18. In some cases, these disorders can come to light in a single episode such as depression triggered by the death of a relative, while in others they may repeat from time to time, such as anxiety attacks in specific situations, or can be continuous, such as autism.
Natália Gregorini
More than a decade ago the medical and psychological community ceased to view mental disorders only as mind or behavioral problems, and started to see them as brain illnesses, taking hold as the organ develops and matures. According to one of the most accepted theories in these areas, the disorders result from the interaction between the social, economic, psychological, and cultural conditions in which the individual lives—environmental factors—and their biological propensity for the issue to develop, determined by their genes. Repeated physical and psychological ill-treatment and other stressful events experienced in childhood and adolescence would continually interact with the genes that determine susceptibility to psychiatric conditions, at some point leading to the development of these disorders (see Pesquisa FAPESP issue nº 232).
In rare phases of life these changes are as rapid and intense as those of the transition from childhood to adolescence and the beginning of adult life. From a biological point of view, the hormones start to prepare the body for the reproductive age, while the brain undergoes radical changes as the areas responsible for attention, memory, language, and planning, along with the structures that control emotions, mature (see Pesquisa FAPESP issue nº 316). From a psychological and social standpoint, they increase the capacity for consciousness of actions and thoughts, and the need for group acceptance, along with entry into the employment market or progression into university life.
On examining how the prevalence of these disorders varies by age group, the JAMA Psychiatry study authors confirmed that they may have very different trajectories, and helped to put numbers to the phenomena that psychiatrists were seeing during clinical practice, but whose frequency was not very well documented.
For example, two of the most common psychiatric disorders in the 5–9 age group are attention deficit hyperactivity disorder (ADHD), marked by difficulties in paying attention, impulsiveness, and restlessness, and conduct disorder, characterized by a challenging, antisocial, and more aggressive attitude. Occurring more frequently in males, these disorders start early: 2.1% of children between 5 and 9 years of age have ADHD, and 1% present conduct disorder; the peak (2.9% and 3% respectively) occurs between the ages of 10 and 14, becoming less prevalent after this age group (see graphics).
Depression and anxiety, two very frequent psychiatric disorders through different phases of life, initially appear in low proportions (0.1% and 1.3% respectively) and continually grow in numbers up to the beginning of adulthood: 3.9% of individuals between 20 and 24 have depression, and 4.6% have anxiety (see charts on page 54). Other conditions, such as intellectual deficiency or autism, present with an almost constant prevalence across all the age groups evaluated, while the onset of alcohol- and drug-use disturbances occurs a little later, beginning to manifest at the beginning of adolescence.
“People think that children and teenagers have the same chance of having ADHD, depression, or anxiety. This is not true. An important aspect of this work is to highlight the most frequent disorders in each age group. This data is paramount in enabling health and education professionals to identify problems early and refer young people for specific diagnosis and appropriate treatment,” says psychiatrist Rodrigo Bressan, of the Federal University of São Paulo (UNIFESP), who commented on the study at the request of Pesquisa FAPESP. “Another factor is that the findings are based on data from 2019, and will serve as a parameter for future studies into how the COVID-19 pandemic has affected the mental health of children and teenagers.”
As well as estimating the prevalence, Kieling and his collaborators calculated the impact of these disorders on people’s lives, using a metric known as “years lived with disability” (YLD), which considers the gravity of each disorder and the time period over which they cause limitations.
In 2019, mental disorders presented by people between 5 and 24 accounted for 31.1 million YLD. This is almost double the second- and third-placed, respectively neurological and skin conditions, and corresponds to 20% of the impact (154 million YLD) of all other nonfatal conditions affecting people in this age range. The period between childhood and the beginning of adulthood concentrates a fourth of the total impact of mental disorders over a lifetime.
“A considerable part of countries’ health budgets should be allocated to early prevention and treatment of mental disorders,” concludes Kieling, whose group is currently investigating the prevalence of these issues among Brazilians between 5 and 24 years of age. “This would prevent significant harm in later life.”
Scientific articles
KIELING, C. et al. Worldwide prevalence and disability from mental disorders across childhood and adolescence: Evidence from the global burden of disease study. JAMA Psychiatry. Jan. 31, 2024.
KIM-COHEN, J. et al. Prior juvenile diagnoses in adults with mental disorder: Developmental follow-back of a prospective-longitudinal cohort. JAMA Psychiatry. July 2003.
