Review PaperAn overview of systematic reviews on the public health consequences of social isolation and loneliness
Introduction
Alone and feeling sick: do isolation and loneliness carry specific risks to health? In populations throughout the world, social isolation (defined as an objective lack of interactions with others or the wider community) and loneliness (defined as the subjective feeling of the absence of a social network or a companion) are common. Surveys in Europe and the USA estimate the prevalence of loneliness ranges from 5% to 43% in the elderly,1, 2, 3, 4 with similar figures for China.5 While loneliness may be more common in the elderly, it also affects younger age groups.6 Precise estimates for the prevalence of loneliness and social isolation are difficult to obtain due to variation across the life course; cultural and gender differences with respect to how prepared individuals are to talk about them from a personal perspective and the use of many different measurement scales, some of which are based on self-report questionnaires while others involve more objective assessment of social contact or networks (or a combination of both).
Loneliness and social isolation have both been associated with ill health, but determining causality is difficult as much of the research in this area involves observational studies. Researchers have primarily focused on the association with mortality, mental and cardiovascular health. Biological pathways have been suggested as an explanation for the effect of loneliness and social isolation on health including reduced levels of protective hormones leading to adverse effects on heart rate, blood pressure and the repair of blood vessel walls; downregulation of the immune system and neuroendocrine dysregulation from a paucity or poor quality of sleep.7, 8, 9, 10 Lonely individuals may be more likely to initiate harmful health behaviours such as smoking, excess alcohol consumption, overeating or transient sexual encounters as a psychological relief mechanism. They may then go on to maintain these harmful behaviours if they are less exposed to healthy behavioural norms or have less access to health advice as a result of fewer social contacts.7, 11 While social networks of friends and family can support healthy behaviours, they may also allow unhealthy behaviours to become normative.12 Stress responses as a result of perceived social isolation can adversely precondition the neuroendocrine system, with genetic differences determining the degree to which this might occur.13 Socially isolated individuals may suffer more stress than others due to their lack of social networks and support, and when they do, they might be more likely to withdraw into themselves.7
Although the exact causal pathways remain unclear, given the prevalence of social isolation and loneliness, it is important to have a clear understanding of their consequences to the individual and society. The evidence base on the impact of social isolation and loneliness has expanded over recent decades and now includes many reviews with different health foci. To provide decision-makers with the evidence they need to assess and tackle the public health challenge associated with weaker social relationships, we conducted an overview of reviews on the health implications of loneliness and social isolation. Our aims were to provide a clear summary of the evidence on the wider consequences of social isolation and loneliness based on systematic principles; identify any differences from findings of the many non-systematic reviews that have been published; clarify the direction of causality; and determine whether there are clear differences in consequences observed for the perceived state of loneliness vs the objective state of social isolation.
Section snippets
Methods
Methodology for this overview followed recognised guidance for conducting systematic overviews.14, 15 The following databases were searched from 1950 to March 2016: Web of Knowledge; SCOPUS; EMBASE; ASSIA; Medline; PsycINFO; Campbell Collaboration and Database of Abstracts of Reviews of Effects, using the terms social environment; social isolation; social vulnerability; social engagement; loneliness and psychosocial support.
Systematic reviews (including narrative reviews and meta-analyses)
Results
The search process of eight databases identified 90 papers (40 systematic reviews, 47 non-systematic reviews and three metasyntheses) that considered social isolation, loneliness, social relationships or networks (Fig. 1). Of the forty systematic reviews included in this overview, ten involved a meta-analysis. Eight reviews were undertaken in two or more countries, while the rest were carried out by teams from single countries, all from the developed world except one. All were published between
Mortality and general health
Two meta-analyses of cohort studies identified a significant association between social isolation, loneliness and social network size with all-cause mortality, identifying odds ratios of increased likelihood of mortality for social isolation (excluding suicide) of 1.29 (95% confidence interval [CI] 1.06, 1.56), for loneliness 1.26 (95% CI 1.04, 1.53) and living alone 1.32 (95% CI 1.14, 1.53);19 and hazard ratios for all-cause mortality for greater social participation of 0.87 (95% CI 0.82,
Main findings
This overview has identified that there is strong evidence that both social isolation and loneliness are associated with increased all-cause mortality. Although proof of causality cannot be confirmed, this may be mediated through the cardiovascular system and mental health. Only limited evidence was identified for an association with other physical health conditions, including cancer, and evidence for the effects of social isolation and loneliness being mediated through behaviours is less
Acknowledgements
Acknowledgements are due to Judy Wright and Natalie King who provided support on the search process.
Ethical approval
Ethical approval was not required for this secondary research.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Competing interests
All authors state that they have no competing interests.
Additional information
N.L.H., D.B., K.B., S.T. and V.T. undertook the overview, N.V. provided input into the analysis of measures using the framework and W.C. provided guidance on
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