The meta-epidemiologic results of this work show that mental disorders have onset when dramatic biological changes in the brain occur, from childhood, through adolescence, to adulthood, that involves grey-matter density, cerebral metabolic rate, synaptic density, white matter growth and myelination [41]. The in-depth, robust epidemiological evidence provided here has several clinical implications. Firstly, the onset of the first mental disorder before age 14, 18 and 25 in one third, half and 62.5% and peak/median age of 15.5/18 years demonstrate that adult mental disorders originate early during the neurodevelopmental phases of life and peak, in pooled mental disorders, by mid to late adolescence [42–44]. Given that mental disorders are one of the five most common ailments leading to morbidity, mortality and dysfunction among young people worldwide [45], the current findings are relevant to policymakers and healthcare providers. These results suggest that the next generation of mental health research should prioritise designing and funding global early interventions [5, 46] and indicated, selective and/or universal preventive interventions for mental disorders during mid/late adolescence and young adulthood that are currently lacking [8].
