Background
Wide differences in health exist between places in the UK, underscored by economic inequalities. Preston, an economically disadvantaged city in England, implemented a new approach to economic development, known as the Community Wealth Building programme. Public and non-profit organisations modified their procurement policies to support the development of local supply chains, improve employment conditions, and increase socially productive use of wealth and assets. We aimed to investigate the effect of this programme on population mental health and wellbeing.

Methods
Difference-in-differences techniques compared trends in mental health outcomes in Preston, relative to matched control areas before (2011–15) and after (2016–19) the introduction of the programme. Outcomes were antidepressant prescribing, prevalence of depression, and mental health related hospital attendance rates using data provided by National Health Service Digital, the Quality and Outcomes Framework, and the Office for National Statistics. Additional analysis compared local authority measures of life satisfaction, median wages, and employment with synthetic counterfactuals created using Bayesian Structural Time Series.

Findings
The introduction of the Community Wealth Building programme was associated with reductions in the prescribing of antidepressants (1·3 average daily quantities per person [95% CI 0·72–1·78) and prevalence of depression (2·4 per 1000 population [0·42–4·46]), relative to the control areas. The local population also experienced a 9% improvement in life satisfaction (95% credible interval 0–19·6%) and 11% increase in median wages (1·8–18·9%), relative to expected trends. Associations with employment and mental health related hospital attendance outcomes did not reach statistical significance.

Interpretation
During the period in which the Community Wealth Building programme was introduced, there were fewer mental health problems than would have been expected compared with other similar areas, as life satisfaction and economic measures improved. This approach potentially provides an effective model for economic regeneration potentially leading to substantial health benefits.