The association of leisure time activities with specific mental disorders has mainly remained unclear because of lack of such research. This study analyzed the association of different levels of social leisure time activity during adolescence (ages 15–16 years) with the incidence of mental disorders during adolescence and young adulthood between the ages of 16–33 years. The study population consisted of 6838 (females 51.5%) participants from the longitudinal follow-up study, the Northern Finland Birth Cohort 1986, covering 72% of the total 1986 birth cohort. Psychiatric morbidity of the participants was followed through nationwide health registers until the end of the year 2018 when the participants were 33 years old. High social leisure time activity in adolescence associated with lower incidence of psychiatric disorders in general, and specifically, with affective, anxiety, and substance use disorders. Low social leisure time activity was related to increased incidence of any psychiatric disorder in general, and particularly to anxiety and behavioral disorders. In terms of prevention of mental disorders, these study findings encourage families, schools and other communities to continue to enhance and develop community-based social leisure time activities for children and adolescents.

Research indicates that adolescent psychological symptoms are associated with subsequent mental health disorders. Studies also show the association of leisure activity with improved current and future mental health. However, research is limited on whether social leisure time activity is a mediating link in the association between psychological symptoms and later psychiatric morbidity. We examined whether adolescence-related social leisure time activity, per se, is a mediating link in the association between adolescent psychological symptoms and later psychiatric morbidity. The study population was based on the Northern Finland Birth Cohort 1986 Study (NFBC 1986; n = 6709; 3227 males). Psychological symptoms at age 15–16 years were measured with the Youth Self Report (YSR) questionnaire. Study participants’ psychiatric morbidity by the age of 33 years was assessed using the diagnoses from the nationwide health care registers. Our results showed an association between psychological symptoms and leisure time activities that varied depending on the level of social activity. Leisure time activity was found to be a mediating link between psychological symptoms in adolescence and psychiatric disorders in early adulthood. Adolescence-related leisure time activities, which differed with regard to social interactions, appeared to serve as a mediating link between adolescent psychological symptoms and later onset of psychiatric disorders. Socially active leisure time during adolescence is related to better long-term mental health, while socially inactive leisure time associates with the likelihood of later psychiatric morbidity. To prevent psychiatric disorders, enhancing such leisure time activities in society is highly recommended.