Loneliness → Depression
Higher Loneliness increases Depression.
Hysing 2026 followed 10,460 Norwegian university students: those in the highest fifth of a 2022 Three-Item Loneliness Scale score, against the lowest fifth, had more CIDI major depressive episodes a year later (relative risk 2.02 in women and 2.64 in men after age and baseline Hopkins symptoms).
Observational · Low · N=10460
The association disappears when you account for other factors, like socioeconomic status or healthy-user bias.
Mechanism
The authors treat loneliness as a felt gap in companionship, not a head count of friends. They think that gap wears on mood through isolation, left-outness, and a thin campus network. They do not isolate one biological path. Hysing, Petrie, Harvey and Sivertsen (2026) invited every full-time Norwegian student aged 18 to 35 in the 2022 Students' Health and Wellbeing Study. 53,362 answered. 16,418 were drawn for a 2023 diagnostic follow-up. 10,460 completed at least one CIDI 5.0 section. Loneliness was the Three-Item Loneliness Scale in 2022. The outcome was a current major depressive episode on a self-administered CIDI about twelve months later. Students with a 12-month or lifetime episode who were not currently depressed were dropped from the models. Highest versus lowest loneliness fifth, age only: relative risk 6.45 (5.14 to 8.07). After age and a high Hopkins Symptoms Checklist score: 2.02 (1.58 to 2.63) in women and 2.64 (1.63 to 4.49) in men. The dose ran through lacking companionship, feeling left out, and feeling isolated. Feeling isolated very often versus never sat at 3.51 in men and 2.28 in women after the same adjustment. Below the Hopkins cutoff the top fifth sat at 3.74 (2.66 to 5.28).
Caveats
Nobody assigned loneliness. These are students who answered a survey and then a diagnostic interview. Observation alone cannot close the backdoor, so the stamp stays smoke. More papers of the same design do not settle the claim. Baseline mood sits on the backdoor. Adjusting for Hopkins symptoms cut the relative risks by about 70 percent. The authors still cannot rule out reverse flow: depression can make campus feel empty. They omitted people with a past episode who were well at the CIDI, so this page is current 30-day MDE, not a first-ever diagnosis in a depression-free cohort. The SHOT response was 35 percent. The CIDI sample was 70.6 percent women, mean age 24, slightly lonelier than invitees who skipped. Follow-up was one year. The T-ILS items are felt isolation. They are not living alone and not a network count. This is a journal entry, not medical advice and not a reason to join a group, to treat a number, or to diagnose a friend.
Effect
qualitative. Hysing 2026: SHoT 2022 T-ILS quintiles to CIDI-5 MDE 2023. n=10460 students 18-35. Highest vs lowest: RR 2.02 women, 2.64 men after age and HSCL. Observational. Archive n null.
Nodes
Named confounders
Cite this page
What Causes What. “Loneliness → Depression.” https://whatcauseswhat.org/edges/e-loneliness-depression (atlas updated 2026-09-02).
Papers
- From loneliness to depression: A longitudinal diagnostic study among Norwegian university students.
M Hysing, KJ Petrie, AG Harvey, B Sivertsen · 2026 · Social psychiatry and psychiatric epidemiology