Trends in millennial adolescent mental health and health related behaviours over ten years: a population cohort comparison study

Background There is evidence that mental health problems are increasing and substance use behaviours are decreasing. This paper aimed to investigate recent trends in mental ill-health and health-related behaviours in two cohorts of UK adolescents in 2005 and 2015. Method Trends in harmonised mental ill-health (depressive symptoms, self-harm, anti-social behaviours, parent reported difficulties) and health related behaviours (substance use, weight, weight perception, sleep, sexual intercourse) were examined at age 14 in two UK birth cohorts; Avon Longitudinal Study of Parents and Children (ALSPAC, N=5627, born 1991-92) and Millennium Cohort Study (MCS, N=11318, born 2000-02). Prevalences and trend estimates are presented unadjusted and using propensity score matching and entropy balancing. Results Depressive symptoms (9% to ∼15%) and self-harm (11.8% to ∼14.5%) increased over the 10 years. Parent-reported emotional difficulties, conduct problems, hyperactivity and peer problems were higher in 2015 compared to 2005 (5.7 – 9% to 9 – 18%).Conversely, substance use (tried smoking 9% to 3%; tried alcohol 52% to ∼43%, cannabis 4.6% to ∼4%), sexual activity (2% to ∼1%) and anti-social behaviours (6.2 – 40.1% to 1.6 – 28%) were less common or no different. Adolescents in 2015 were spending less time sleeping, had higher BMIs and a greater proportion perceived themselves as overweight. Conclusion Given health-related behaviours are often cited as risk-factors for poor mental health, our findings suggest relationships between these factors might be more complex and dynamic in nature than currently understood. Striking increases in mental health difficulties, BMI and poor sleep related behaviours highlight an increasing public health challenge.