In an increasingly divided world, health inequalities too are growing. Acting early in the life course may send children from disadvantaged backgrounds on positive health trajectories that will set them up for the rest of their lives 🪴

5. Finally, this work cannot be done without the collaboration of multidisciplinary teams. Social scientists, biologists and biostatisticians alongside policy makers, data custodians and consumers.

4. Most of the studies we reviewed were in high-income countries. In low- and middle-income countries, results were null or inverse. What are the context-specific exposures that lead to socioeconomic inequalities in inflammation? To answer this, we need a diversity of study locations.

3. Inflammation, when measured by single or few inflammatory biomarkers at one time point, captures only a static image of immune functioning. Measuring immune responsiveness, capacity and resolution may give us a better idea of how early-life exposures affect long-term immune phenotype.

2. SEP is just one aspect of the social environment – what about those overarching structural forces such as systemic racism and class, or those downstream factors such as housing quality and family emotional environment?

1. SEP is a diffuse and multi-factorial construct. Conceptualising and utilising a broader range of indicators will help to illuminate the mechanisms by which socioeconomic inequalities in inflammation arise.

Here are our recommendations:

However, inconsistencies within and across country contexts had us asking: how can those of us working with life course and longitudinal data make more meaningful inferences about how the social environment impacts long-term immune phenotype, considering diverse populations around the world?

These results highlight the importance of addressing poverty and socioeconomic disadvantage early in children and adolescents' lives.

From 41 studies, we found that the majority documented consistent associations between lower socioeconomic position (SEP) and higher inflammation, across multiple individual, household and neighbourhood-level indicators.