Psychology › Mental health & disorders › Depression and mood disorders
Loneliness and social isolation
Surgeon General advisory 2023· Concept
Well replicatedStrong, repeated evidence.
Loneliness is the painful sense that one's relationships fall short of what one needs; isolation is the objective lack of contact.
See it on the Psychology map →What it says
The two differ: some people live alone happily, others feel lonely in a crowd or a marriage. In 2023 US Surgeon General Vivek Murthy issued an advisory calling loneliness an epidemic, citing surveys in which about half of American adults reported it. A 2010 meta-analysis of 148 studies by Julianne Holt-Lunstad linked strong social ties to about 50 percent better odds of survival. Psychologist John Cacioppo showed loneliness makes people more alert to social threat, which can deepen withdrawal.
Why it matters
Loneliness is linked to depression, heart disease, dementia and early death. It is common after retirement, divorce or widowhood, and it can be changed.
The evidence
Long-term cohort studies and meta-analyses link it to illness and death; a 2011 meta-analysis found programs that challenge negative social thinking reduce loneliness more than simply adding contact.
Open questions
Whether loneliness is really rising is unclear; long-term data are mixed. The popular 'as bad as 15 cigarettes a day' comparison is a rough, debated estimate.
Connections (3)
▸Loneliness and social isolation reflects a shortfall in Close relationships: adult attachment and marriageWell replicated
The connection
Loneliness measures the gap between the connection people want and what they have. Close, supportive relationships, especially a secure partner or confidant, are the strongest buffer; quality matters more than the number of contacts. Marriage helps on average, but an unhappy one can be lonelier than living alone.
Who showed it and when
Daniel Perlman and Letitia Anne Peplau's 1981 'discrepancy' definition of loneliness; later work by John Cacioppo and Louise Hawkley in Chicago.
The evidence
Surveys consistently find relationship quality predicts loneliness better than the number of contacts or whether someone lives alone.
Open questions
Whether the decline in close friendships reported in some US surveys is real, and how online contact fits in, remain debated.
▸Loneliness and social isolation raises the risk of Dementia and Alzheimer's diseaseMixed evidence
The connection
Lonely, isolated older adults develop dementia at higher rates. Possible routes include less mental stimulation, more stress hormones and inflammation, less exercise, and depression. A 2024 Lancet commission listed social isolation among 14 modifiable risk factors for dementia.
Who showed it and when
Large cohort studies in the US, UK and elsewhere since the 2000s; the Lancet Commission on dementia prevention (2017, 2020, 2024).
How solid is it?
A 2024 meta-analysis of over 600,000 people linked loneliness to about a 30 percent higher dementia risk, but these are associations, not experiments.
Open questions
Early dementia itself can cause withdrawal, so part of the link may run backward; whether reducing loneliness lowers risk has not been proven.
▸Loneliness and social isolation raises the risk of Depression and mood disordersWell replicated
The connection
Loneliness predicts later depression even after accounting for earlier symptoms, and depression in turn makes people withdraw, so the two feed each other. Lonely people tend to read ambiguous social signals as rejection, which deepens isolation.
Who showed it and when
John Cacioppo's Chicago study of middle-aged and older adults showed in 2010 that loneliness predicted rising depressive symptoms over five years.
The evidence
Cohort studies that track both over time show the effect runs in both directions, with loneliness predicting future depression in many studies.
Open questions
Whether reducing loneliness prevents depression is not yet shown by large trials; shared causes such as personality may explain part of the link.