Social isolation is linked to high levels of morbidity and mortality in the general population [1,2]. The strength of this association is comparable to that of established risk factors such as hypertension, obesity and smoking [3]. Having friends provides emotional and practical support and helps people to cope with life stressors [4]. Relationships with friends may also positively affect physical and mental health by improving health behaviours and increasing selfefficacy, self-esteem and morale [2,4]. The role of friends as a source of social support is becoming increasingly important in contemporary society [5,6], as a consequence of changes in family structure and of the increased number of people living alone [7].

People with affective disorders are likely to be at high risk for social isolation [8]. Depressive and anxiety symptoms may reduce patients’ motivation to engage in social relationships and activities [9]. On the other hand, high levels of excitement and activation, as observed in mania, may make patients appear unpredictable and dangerous so that others avoid establishing contact and relationships with them [10,11].

Several research studies have addressed the social functioning of patients with major mental disorders, including mood disorders. However, their findings are difficult to compare because of the different definitions of the key concepts (i.e. “social networks”, “social contacts” and “social relationship”) and the different methodologies adopted.

There is a need for further research in the area in order to overcome the heterogeneity of the conceptualisations as well as of the assessment tools. Future studies should use comprehensive measures to assess both objective (quantitative) and subjective (qualitative) characteristics of the social relations of people with mood disorders. This would allow us to better understand the social needs of these patients and how these needs vary in different phases of mood disorders. New research should also take into account the significant changes in social relationships following the advent of online social networking [12].

This research evidence should guide the development of mental health care strategies to reduce the risk of social isolation in people with mood disorders. This seems key to improve their mental and physical health outcomes and their quality of life.