Background There is a well-established link between area-level socioeconomic deprivation and psychiatric admission rates. Social capital has been proposed as a possible protective factor that may buffer economically deprived communities, but it may be disrupted in areas with high population turnover. This study aims to test whether population turnover, hereafter called churn, moderates the social gradient of psychiatric admissions.

Methods Population churn rates, low income rates and psychiatric admission rates for 1909 lower super output areas in Wales were analysed using Poisson generalised linear mixed-effects models. Additional analyses explored the impact of deprivation measured more generally and the potential confound of population density.

Results Population churn moderated the association between socioeconomic deprivation and psychiatric admission rates, such that greater social gradients in admission rates were found in areas with greater churn. Economic deprivation and churn were also found to be independently positively associated with admission rates. These relationships remained significant when using a broader measure of deprivation and after adjusting for population density.

Conclusion High churn appears to exacerbate the detrimental effects of economic deprivation on mental health as well as being a risk factor in its own right. Residential stability rates should be considered when designing and implementing policies which aim to understand, prevent and treat mental health problems in at-risk communities.