This systematic review and meta-analysis examined the association between objective olfactory impairment (OOI) and subjective olfactory impairment (SOI) with depression in population-based studies of adults, drawing from 23 studies (17 independent cohorts, N = 187,056; mean age 63.6 years; 63% female).
SOI was consistently associated with depression (OR 1.56, 95% CI 1.19–2.05; I² = 79%), robust even in low-risk-of-bias studies (OR 1.71). OOI showed a weaker association with objective depression (OR 1.26, 95% CI 1.02–1.56; I² = 53%) that became non-significant after publication bias adjustment (OR 1.12, 95% CI 0.87–1.44), though it remained significant in older adults (≥65 years) and individuals with anosmia.
- High heterogeneity for SOI (I² = 79%) limits confidence in pooled estimates. - OOI's association with depression did not survive publication bias correction in the overall sample, suggesting potential overestimation. - Most included studies are cross-sectional, preventing causal inference.
Clinicians evaluating older adults — especially those with anosmia or self-reported smell loss — should be aware of a meaningful association with depression and consider screening. Causal direction remains unclear, so olfactory impairment should be viewed as a potential marker, not a confirmed cause, of late-life depression.
