TLDR
Feeling lonely is more than being physically alone. When loneliness continues, it can affect thinking, behavior, sleep, and body health, so effective help may need to change negative expectations about relationships.
Summary
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1 Study Aim
The authors aimed to review how loneliness affects mental and physical health, explain the processes behind these effects, and assess existing interventions. They distinguish perceived social isolation from simply having few social contacts. Their model proposes that loneliness creates a repeating cycle of social threat, negative expectations, withdrawal, and worsening disconnection. Loneliness may harm health through linked changes in thoughts, actions, sleep, and body functioning.
2 Study Design
The authors conducted a theoretical and empirical review of longitudinal, experimental, diary, physiological, immune, and gene-expression studies. They also reviewed intervention research and reported a meta-analysis combining 50 studies published between 1970 and September 2009. These included 20 randomized comparison studies, 18 nonrandomized studies, and 12 pre-post studies. The review covered interventions targeting social skills, support, social opportunities, and maladaptive social thinking. No single participant sample represented the entire paper. The researchers combined many kinds of evidence to explain loneliness and compare ways of reducing it.
3 Findings
The review reports that loneliness predicts higher risks of cardiovascular problems, illness, death, depression, cognitive decline, and Alzheimer’s disease. It is also linked with poorer sleep quality, reduced physical activity, obesity, alcohol misuse, altered stress hormones, immune problems, and inflammation. The authors propose that hypervigilance (automatic alertness for social danger) encourages negative interpretations and withdrawal, creating a self-reinforcing cycle. They also describe possible glucocorticoid receptor insensitivity (weaker cellular response to stress hormones), which may promote inflammation. In randomized studies, interventions changing maladaptive social thinking showed larger effects than social support, skills training, or increased social contact. However, evidence that reducing loneliness improves physical health remains limited, and one group-activity trial improved health without reducing loneliness. The most promising help may address negative social expectations, not only increase opportunities to meet people.