Loneliness and social isolation are increasingly recognised as public health concerns. In 2018, the UK Government launched its first loneliness strategy and earlier this year the US Surgeon General Vivek Murthy published a report describing loneliness and isolation as “profound threats to our health and wellbeing”. While it is evident that there is a strong relationship between loneliness, social isolation and various health outcomes, there is less clarity about whether  loneliness and social isolation actually cause these poor health outcomes. With around one in five people in the UK reporting feeling lonely at least some of the time, it is crucial that we understand whether loneliness and social isolation may cause poorer health.

We wanted to fill a critical evidence gap so that we could provide policymakers and public health professionals with evidence about the effect of loneliness and social isolation on health. A better understanding of this relationship will enable those working in the sector to have greater confidence in deciding whether tackling loneliness could improve the number of healthy years lived in the UK.

Previous research has established a relationship between loneliness (the subjective feeling of being alone) and social isolation (an objective lack of social contacts and interactions) with various health outcomes. However, much of this research is correlational and potentially plagued by issues of confounding causality, where a third factor may be influencing both health and loneliness, and reverse causality, where it could be poor health which causes greater loneliness. Since loneliness and social isolation are gaining prominence as public health issues, it is crucial to understand whether they have a causal impact on health.

We used research methods rarely applied in this field – specifically Mendelian randomization and sibling control analysis. Mendelian randomisation uses genetic variation to assess causal effects, while sibling control analysis leverages sibling relationships to account for unmeasured family influences. These approaches can help to address confounding and reverse causality concerns. Our analyses utilised genome-wide association and major cohort studies, evaluating four health outcome categories: physical health, mental health, subjective wellbeing and general health. By carrying out this research, we aimed to strengthen the evidence base examining whether loneliness and social isolation impact our health.

University of Bristol - Dr Zoe Reed, Dr Robyn Wootton (Lovisenberg Hospital), Dr Hannah Sallis and Professor Marcus Munafò

Amsterdam UMC - Dr Margot Van De Weijer, Dr Jorien Treur

University of Manchester - Professor Pamela Qualter