Before the damage is done: Early childhood hyperactivity difficulties in adolescents with deliberate self-harm - findings from the DALSC cohort.

Background: Deliberate self-harm (DSH) is a growing issue among Danish adolescents, and a dramatic increase in the incidence of DSH has been observed since the turn of the millennium. The importance of early childhood factors on later development has been established, but research on the trajectories of DSH is still scarce, and longitudinal studies are much needed.

Method: Participants were 3,291 children and their mothers from The Danish Longitudinal Survey of Children (DALSC), a Danish population-based birth cohort from 1995. Logistic regression and mediation analyses were used to examine significant early childhood determinants of self-harming behavior in adolescence.

Results: The study found that 17.9% of the children had a history with DSH at the age of 18 years. A significant relationship was found between the likelihood of DSH at the age of 18 years and hyperactivity difficulties assessed through the Strengths and Difficulties Questionnaire (SDQ) at 3 and 7 years of age. Using a mediation model, it is documented that difficulties in peer relationships at the age of 11 years is a partial mediator explaining 19% of the variation.

Limitations: i) a vague definition of self-harm in the questionnaires; ii) lack of sample representation as children of lower socio-economic groups have lower participation rates, and only Danish-ethnicity children have been sampled; iii) possibility of omitted variable bias.

Conclusion: The adolescents engaging in DSH are experiencing a more complex range of psychosocial problems than those who do not have experience with DSH. The main finding of the study is that hyperactivity as a risk factor for the development of DSH in adolescence can be identified as early as 3-7 years of age. This relationship between the very early occurring hyperactivity and later DSH, to the best of our knowledge, has not previously been described.