A growing number of studies suggest that social isolation and loneliness are associated with premature mortality and are more prevalent among people with mental illness than in the general population, outlining many potential paths to disease still to be elucidated. The purpose of this meta-analysis is to examine the relationship between loneliness, social isolation, and established cardiovascular/metabolic risk factors and disorders, especially in severe mental illness, and to account for potential heterogeneity in the literature.