Socio-economic inequalities in the density of outdoor unhealthy food and drink advertising and its concentration near primary schools in Madrid

Advertising of unhealthy foods and beverages is a driver of inequalities in dietary behaviours and a contributor to childhood obesity. Outdoor advertising is an influential channel; however, no previous research in Spain has examined whether its frequency and persuasive strategies vary across socioeconomic contexts. This study aims to address this gap. Cross-sectional observational study on food and drink advertisements in public thoroughfares of eight Madrid neighbourhoods. Products were classified according to the World Health Organisation nutrient profile model. We calculated the density of unhealthy advertisements by socio-economic level, the percentage around schools and the proportion of advertisements employing marketing techniques. Differences were analysed using Chi-squared tests. 98.6% of advertisements were unhealthy. The density of unhealthy advertisements in low-income neighbourhoods was 80% higher than that in high-income neighbourhoods (2.2 vs. 1.2). The concentration around schools (89.4% of advertisements were located within a 250-metre radius) was also greater in low-income neighbourhoods. Persuasive marketing techniques were infrequent and less common near schools and in low-income neighbourhoods. The higher density of unhealthy food advertisements around schools in low-income Madrid neighbourhoods poses a higher risk of exposure. Limiting outdoor advertising in Spain will reduce this exposure and its socioeconomic inequalities.