Does loneliness shorten your life?
At age 40, the difference between the best and worst answer here is about 3.6 years of life expectancy — 3.7 for men and 3.4 for women. That is the gap between “close, reliable people” and “genuinely lonely”, holding everything else constant.
This is the factor that surprises people most, and the one almost never mentioned in a health check. Social isolation carries mortality risk of a magnitude usually reserved for smoking and obesity — and unlike those two, it is rarely framed as a health problem at all.
What each answer costs, at 40
| Answer | Hazard ratio | Years vs. best |
|---|---|---|
| Close, reliable people | 0.90 | best |
| A few good ones | 0.98 | −0.9 |
| Fairly isolated | 1.14 | −2.4 |
| Genuinely lonely | 1.28 | −3.6 |
Computed from the SSA 2023 period life table with this factor’s hazard ratio applied and every other factor held neutral. Source: Holt-Lunstad et al., PLOS Medicine 2010 (148 studies).
Does it matter less as you get older?
Yes, and by a lot. A hazard ratio applies to the years you have left, so the same answer costs less in absolute terms the later you are asked it. That is an argument for changing it early, not for concluding it no longer matters.
| If you are now | Men | Women |
|---|---|---|
| 30 years old | 4.0 yrs | 3.6 yrs |
| 40 years old | 3.7 yrs | 3.4 yrs |
| 50 years old | 3.4 yrs | 3.2 yrs |
| 60 years old | 2.9 yrs | 2.9 yrs |
| 70 years old | 2.3 yrs | 2.4 yrs |
What the evidence actually shows
Holt-Lunstad and colleagues meta-analysed 148 studies following 308,849 people. Those with strong social relationships had 50% greater odds of survival over the follow-up period. The authors noted the effect size was comparable to quitting smoking and exceeded that of obesity and physical inactivity — a comparison that has held up in later replications.
What to do about it
Social isolation carries mortality risk in the same league as smoking. Two or three real friendships, actually maintained, is a measurable intervention.
Where this number is weak
Causation runs in both directions: illness isolates people as surely as isolation makes people ill. But the effect survives adjustment for baseline health, and the plausible mechanisms — worse sleep, higher inflammation, nobody to notice symptoms early, nobody to drive you to hospital — are mundane rather than mystical.
More generally: these are observational cohorts, which show association rather than proof of cause. The full methodology sets out every simplification the model makes.
What is it costing you?
The calculator weighs this against your other nine factors and ranks them.
Then make it count. The Extension Plan turns your result into a 12-week plan, starting with the habit worth the most years to you · $9. See what is in it →