What we conclude
People with weaker social ties — few contacts or feeling lonely — are more likely to die during follow-up, according to two large reviews of other researchers’ studies. The reviews do not prove that isolation causes death.
What we will not claim
This is not a NOOS study and not city policy. Isolation (few contacts) is not the same as loneliness (feeling alone). A comparison with smoking is an illustration of size from one paper, not a finding that isolation equals smoking. We did not include later WHO death-per-year counts whose method we could not check.
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What the pattern is
When researchers follow large groups of people over years, those with fewer social contacts tend to die sooner. That pattern still shows up in studies that accounted for age, existing illness and similar differences. It does not prove that isolation itself causes death. A person who is already ill may see fewer people, and that can look like isolation causing death when the illness came first.
Two reviews sit behind this page
The 2010 review by Holt-Lunstad, Smith, and Layton combined 148 studies and 308,849 people. Stronger social relationships were linked to 50% higher odds of being alive at follow-up (odds ratio 1.50; 95% confidence interval 1.42 to 1.59), pooled from the least-adjusted model of each study; results varied a lot between studies. The authors called that size of link comparable with quitting smoking. That comparison is an illustration, not a finding that “isolation equals smoking.”
The 2015 review by Holt-Lunstad, Smith, Baker, Harris, and Stephenson combined 70 prospective studies and 3,407,134 people followed for about seven years on average. After adjustments, social isolation was linked to 29% higher odds of death (odds ratio 1.29), loneliness to 26% (1.26), and living alone to 32% (1.32). Unadjusted numbers were larger — up to about 1.83, from only three studies. The authors warn against quoting the raw figures, because reverse causality (illness reducing contact) likely inflates them. The link was stronger in samples whose average age was under 65. Isolation (few contacts) and loneliness (feeling alone) are not the same thing; both were linked to death in this review. The authors write that they cannot confirm causality.
We looked at later World Health Organization pages about social connection. We did not include a round number of deaths per year, because the method behind that figure was not clear enough on the public pages we could check.
What this page is not
It is not a NOOS study. It is not advice to a city. It does not say that measuring isolation like air pollution is proven. That idea is a proposal, not a result of these papers.