Joinpoint analyses of rates on hospital-recorded deliberate self-harm: an update on Danish national trends

Introduction: Deliberate self-harm (DSH) is a public health concern and the high rates among adolescents and females warrant continuous monitoring. The aim of this study was to determine trends in DSH rates by gender and age in Denmark during 2000–2021 using joinpoint regression analysis. Methods: A cohort design was applied to national register data on all individuals aged 10 + years living in Denmark during 2000–2021. DSH episodes were identified in somatic and psychiatric hospital data. Sex- and age-specific incidence rates (IR) were calculated by calendar years. Using joinpoint regression analyses, segments of change and their annual percent change (APC) were identified. Results: The highest DSH rates were observed for males and females aged 19–24 years with IRs of 146.8 (95% CI 142.9–150.7) and 378.6 (95% CI 372.1–385.0) per 100,000 person-years, respectively. Major changes in DSH rates were found for the youngest age groups. A step decrease was found for males aged 19–24 years (-18.4; 95% CI -31.9- -2.3; p = < 0.030) during 2012 to 2015. A significant decline was observed during 2012–2016 for females aged 19–24 years (-18.9; 95% CI -26.8 – -10.2; p = 0.001). Poisoning was the most frequently used method. Conclusion: Seemingly, the financial recession in 2008 did not affect Danish DSH rates. Significant declines were observed for females in the years where means restrictive measures had been installed; thus, supporting their potential effect. Fluctuations in DSH rates among adolescents and young adults in recent years underscore the importance of continued monitoring.