Background Most adolescents do not achieve the recommended level of physical activity (PA) in the UK. The ethnic density hypothesis suggests that living in areas with higher proportions of people of the same ethnicity may confer health benefits. We explore whether school and neighbourhood ethnic densities are associated with adolescent utilitarian and leisure physical activity behaviours and whether these effects contribute to explaining ethnic differences in these behaviours.

Methods We used longitudinal data from the Olympic Regeneration in East London (ORiEL) study. In 2012, 3088 adolescents aged 11–12 were recruited from 25 schools in four deprived and ethnically diverse boroughs of East London. Adolescents were followed-up in 2013 and 2014. Own-group ethnic density was operationalised at school- and neighbourhood-levels in 2012/14 and 2011 respectively, and calculated as the percentage of adolescents, in the relevant school or neighbourhood (defined as ‘lower layer super output area’ of their home-address), who were of the same ethnic group. Analyses were restricted to White UK, White Mixed, Black African and Bangladeshi groups. The outcomes were self-reported binary variables: walking to school, walking for leisure, and outdoor PA. We identified potential confounders. We estimated logistic regression models with generalised estimating equations for each outcome and included interaction terms between ethnicity and ethnic densities. Item non-response was handled using multilevel multiple imputation. Final sample size was 1160 adolescents.

Results At school-level, there was consistent evidence that ethnic density amplifies ethnic differences in walking to school. For each 10 percentage point increase in ethnic density, there was evidence of increased probability of walking to school in Bangladeshi adolescents (OR=1.20; 95% CI 1.09 to 1.31) and decreased probability of walking to school in Black African (OR=0.58; 95% CI 0.45 to 0.75) and White Mixed adolescents (OR=0.51; 95% CI 0.35 to 0.76), after adjusting for confounders. Associations with walking for leisure and outdoor PA were in expected directions but not consistently observed in all ethnic groups.

At neighbourhood-level, evidence was more restricted. Amplification of ethnic differences was found for walking to school in Bangladeshi adolescents (OR=1.31; 95% CI 1.14 to 1.51) and for outdoor PA in White UK adolescents (OR=0.85; 95% CI 0.76 to 0.94).

Conclusion These results suggest that ethnic density contributes to explaining differences in PA by amplifying ethnic differences in some forms of PA. Further research is needed to confirm these results in different populations and for different health behaviours.