Background The burden of mental illness is increasing amongst UK adolescent populations. While many factors thought to have contributed to this rise are likely to have a disproportionate impact on more deprived adolescents (e.g. austerity related cuts to youth services), no previous national studies have investigated the changing and existing relationship between deprivation and reported mental illness. Our study aimed to investigate time-based trends of the prevalence of a long-standing mental health condition (LSMHC), and the relationship between deprivation and LSMHC prevalence.

Methods Data were analyzed from 32 678 adolescents aged 13–24 (stratified into five ‘index of multiple deprivation’ quintiles) from sixteen ‘Health Survey for England’ datasets (2001–2016). Descriptive statistics identified the percentage of adolescents with outcome variable ‘Long standing mental health condition’ and trends in prevalence analyzed over time. The difference between the percentage prevalence in quintile 1 (least deprived) and quintile 5 (most deprived) was calculated to assess for changes in this ‘deprivation gap’ over time. Regression models were utilized to analyze relationships between deprivation and mental illness across four time-bands; 2001–2004, 2005–2008, 2009–2011, 2012–2016.

Findings From 2001–2016: the overall prevalence of a LSMHC increased from 1.9% to 8.2%. The increase was greater among the most deprived quintile (2.9%–10.6%); as a result, the gap between the most and least deprived increased by a factor of 6 (0.9% to 5.7%). The gap between the sexes also increased ten-fold (0.3%–3.1%, boys worse).

Regression models showed that in 2001–4, there was no significant difference in prevalence of a long-standing mental health condition between the most versus least deprived quintiles (OR=1.22 (95% CI 0.82–1.80, p=0.33)); by 2012–16, a highly significant difference was found (OR=1.75 (95% CI 1.22–2.51, p=0.002).

Conclusion Our data show increasing reported prevalence of a mental illness among all adolescents and young adults. The increase is greater among the most deprived, leading to widening health inequalities. These findings advance understanding of the role that deprivation may be playing in the current crisis of mental health problems among young people.