Recent scientific work has established both a theoretical basis and strong empirical evidence for a causal impact of social
relationships on health. Prospective studies, which control for baseline health status, consistently show increased risk of
death among persons with a low quantity, and sometimes low quality, of social relationships. Experimental and quasi-experimental
studies of humans and animals also suggest that social isolation is a major risk factor for mortality from widely varying
causes. The mechanisms through which social relationships affect health and the factors that promote or inhibit the development
and maintenance of social relationships remain to be explored.