It is acknowledged that many mental health conditions have an onset in the first two decades of life, unlike most other non-communicable disorders (e.g., cardiovascular disorders or cancer) which typically have an onset in late adulthood. Identifying key factors such as age of onset, lifetime prevalence, and lifetime morbid risk is essential for understanding the epidemiology of all health conditions, including mental health conditions. This helps to ensure that the correct mix of services is available to provide prompt and effective treatment to affected individuals – such as early intervention for teenagers. Furthermore, it allows us to identify risk factors including morbid risk and estimate the non-fatal burden of these disorders.
The most comprehensive and up-to-date data on age of onset and morbid risk of common mental health conditions were reported in 2007 by the World Mental Health (WMH) survey collaborators. This data was obtained from 17 countries and reported evidence that many mental health conditions first emerge between childhood and early adulthood. However, few studies currently present both age of onset and lifetime prevalence for diverse mental health disorders based on population-based data from multiple countries. To address this, the authors of a recent study aimed to “provide updated and improved estimates of age-of-onset distributions, lifetime prevalence, and morbid risk.”
Design and Methods of the Study
In a cross-sectional analysis, researchers obtained and analysed data from 32 WMH surveys conducted in 29 countries. These cross-sectional, face-to-face community epidemiological surveys were administered between 2001 and 2022 and included the WHO Composite International Diagnostic Interview, a fully structured psychiatric diagnostic interview, used to assess age of onset, lifetime prevalence, and morbid risk of 13 DSM-IV mental health conditions until age 75 years across surveys by sex. The surveys were geographically clustered and weighted to adjust for selection probability and standard errors of incidence rates.
The interviews were conducted in two parts. Part one contained assessments of core mental health conditions (i.e., depression, mania, panic disorder, social phobia, specific phobia, agoraphobia, generalised anxiety disorder, and substance use disorder). Respondents who met lifetime criteria for a specific condition were also asked about the age of onset.
Part 2 of the interview, which included questions about other mental health conditions and correlates, was then administered to all part 1 respondents who met lifetime criteria for any condition and a random subsample, of other part 1 respondents. Cumulative incidence curves were also calculated.
Findings of the Study
The researchers included 156,331 respondents from 32 surveys in 29 countries, including 12 low-income and middle-income countries and 17 high-income countries. The overall weighted response rate across all surveys was 63.6%.
Lifetime Prevalence of Mental Disorders
Lifetime prevalence of any mental health conditions was 28.6% for male and 29.8% for female respondents. Ethnicity was not assessed. Lifetime prevalence of any anxiety disorder was 11.3% for male respondents and 18.8% for female respondents, and of any mood disorder was 9.5% for male respondents and 15.4% for female respondents. The three mental health conditions with the highest lifetime prevalence for male respondents were alcohol abuse (13.7%), major depressive disorder (7.5%), and specific phobia (5.0%). For female respondents, the conditions with the highest lifetime prevalence were major depressive disorder (13.6%), specific phobia (10.0%), and PTSD (5.4%).
Projected Lifetime Morbid Risk
Projected lifetime morbid risk by age 75 years for each mental health condition was higher than the observed lifetime prevalence at the time of interview. Lifetime morbid risk of any mental health condition as of age 75 years was 46·4% for male respondents and 53·1% for female respondents. The three disorders with highest lifetime morbid risk for male respondents were alcohol abuse (21·6%), major depressive disorder (20·1%), and drug abuse (7·9%), and those for female respondents were major depressive disorder (34·0%,), PTSD (12·6%), and generalised anxiety disorder (12·5%). This suggests that, by the age of 75, almost half the population can expect to develop one or more of the 13 mental health conditions considered in this study.
Age of Onset
For the incidence of first onset of any disorder, peak incidence was approximately at age 15 years. At the age of 15 years, males had higher incidence (hazard rate 288.0 per 10,000 participants) than female respondents (228.2 per 10,000 participants). However, across the rest of the lifespan, incidence was slightly higher among female respondents. The ratio of morbid risk to lifetime prevalence shows the relatively high proportion of mental disorders that first occur in childhood, adolescence, or young adulthood.
The data showed that around half of people who develop a mental health condition first develop the condition by the time they turn 19 or 20, for males and females respectively. Notably, in addition to traditional childhood-onset disorders such as ADHD, social phobia, and specific phobia, other common mental health conditions (e.g., major depressive disorder, generalised anxiety disorder, panic disorder, and drug use disorders) were found often to have their first onsets between childhood and early adulthood.
Conclusions of the Authors
These findings indicate that approximately one in two individuals will develop at least one of the mental health conditions considered in this study during their lifetimes. The researchers note that these findings are based on more accurate estimates of age-of-onset distributions than previous studies, and they support the idea that many mental disorders have their first onset during childhood, adolescence, or young adulthood and that some disorders have earlier ages of onset than others.
The authors note that the observation that common mental health conditions often have their first onset between childhood and early adulthood “supports the need to invest in mental health services that have a particular focus on young people.”
While the researchers acknowledge that there were some limitations to their study – including a study period spanning over two decades, use of data based on retrospective reports, and failure to consider comorbidity – the provided insights and estimates will be of value to service planners, researchers interested in the burden of disease, and genetic epidemiologists.