Conversely, for men greater ethnic density was linked to an increased risk.

Conclusions: The most consistent associations with ethnic density are found for psychoses.

For Hispanics there was a significant interaction between gender and same- ethnic density.

Most studies report a null association between ethnic density and health.

Possibly, high levels of social disadvantage inhibit positive effects of ethnic density on health.

Conclusions: Associations between ethnic density and self-rated health are inconsistent and differ by ethnicity and gender.

For women, higher levels of same- ethnic density were associated with a reduced risk of poor self-rated health.

In the White British sample, neither birth weight nor preterm birth was associated with own ethnic density.

Protective ethnic density effects are more common than adverse associations, particularly for health behaviors and among Hispanic people.

Associations between ethnic density and health were tested in multilevel regression models, adjusted for individual covariates and area deprivation.

Limitations of the literature include inadequate adjustment for area deprivation and limited statistical power across ethnic density measures and study samples.

Protective associations between ethnic density and diagnosis of mental disorders were most consistent in older US ecological studies of admission rates.

The aim of this study was to systematically review the literature examining the ethnic density effect on physical health, mortality, and health behaviors.

We go on to discuss processes which may underlie ethnic density effects, and highlight gaps in the literature and opportunities for further research.

Aims: To systematically identify relevant studies, summarise their findings and discuss potential explanations of the associations found between ethnic density and mental disorders.

We situate the research question in the context of contemporary social epidemiology and provide a narrative review of studies of ethnic density and health.