The above studies complement a growing literature demonstrating differences in gene expression in humans as a function of environmental experience. One of the first studies to analyze the relationship between social factors and human gene expression compared healthy older adults who differed in the extent to which they felt socially connected to others (Cole et al. 2007). Using expression profiles obtained from blood cells, a number of genes were identified that showed systematically different levels of expression in people who reported feeling lonely and distant from others. Interestingly, these effects were concentrated among genes that are involved in immune response. The results provide a biological mechanism that could explain why socially isolated individuals show heightened vulnerability to diseases and illnesses related to immune function. Importantly, they demonstrate that our social worlds can exert biologically significant effects on gene expression in humans (for a more extensive review, see Cole 2009).
