Background Childhood bullying is an important policy concern. Nearly half of victims of bullying report thoughts about suicide and self-harm with negative impacts extending across the life-course. Being bullied in childhood is common, socially patterned, however, factors explaining social inequalities in being bullied are unclear. Using a contemporary United Kingdom (U.K.) birth cohort, we aimed to assess and explain social inequalities in the risk of being bullied.

Methods Analysis of the U.K. Millennium Cohort Study using a sample of 12 706 children surveyed at four sweeps (aged nine months, three, five and seven years). The main outcome was a binary, child-reported measure of being bullied at age 7. Household income quintile at birth was the main measure of socio-economic conditions. Relative risk (RR) and 95% confidence intervals (95% CI) for being bullied were estimated using Poisson regression, by household income quintile. Sequential models adjusted for risk factors for being bullied, including individual (e.g. emotional resilience, health status including obesity), parental (e.g. maternal mental health and discipline) and peer relationship (e.g. friends) factors. Analysis used Stata/SE with svy commands to account for the sampling design and attrition. Our sensitivity analysis will use parent and teacher reported outcome measures.

Results By age seven, 48.7% (95%CI 47.5%–49.9% [n=6183]) of children self-reported being bullied. There was a social gradient; 53.4% (95%CI 50.6%–56.1%) in the lowest income quintile reported having been bullied, compared to 43.9% (95%CI 41.5%–46.4%) in the highest (RR 1.21 [95%CI 1.10–1.33]). Male sex, young maternal age, higher child BMI and Strengths and Difficulties Questionnaire (SDQ) scores and worse maternal mental health were independently associated with an increased risk of being bullied, whilst having a good friend was protective. Controlling for these factors in the final model attenuated the RR for being bullied for children in the lowest income quintile, compared to the highest, rendering the association non-significant (RR 1.08 [95%CI 0.98–1.19]).

Conclusion Using a nationally representative cohort, about half of seven year olds reported being bullied, with a greater risk in children from the poorest homes. Increased risk was largely explained by social differences in other risk factors for bullying including friends, maternal mental health, and individual factors including emotional resilience and BMI. Interventions addressing these risks and promoting protective factors are likely to reduce social inequalities in being bullied, improving mental health outcomes for the most vulnerable U.K. children. Future research should investigate inequalities in being bullied in adolescents. The self-reported primary outcome is the main study limitation.