Olfactory Training and Patient-Centered Outcomes Beyond Smell: A Systematic Review and Meta-Analysis

Olfactory dysfunction (OD) is associated with diminished quality of life (QOL), depressive symptoms, and cognitive decline, and emerging evidence suggests that olfactory training (OT) may mitigate both OD and its broader impacts. This review aims to systematically evaluate the effects of OT on QOL, depression, and cognitive outcomes.

PubMed, Embase, Cochrane, Scopus, and Web of Science were searched for studies published between 1990 and 2025. PRISMA guidelines were followed for study screening and data extraction. Studies evaluating the effects of OT on QOL, depressive symptoms, or cognitive function were included. Random-effects models were used to pool within-group standardized mean changes (SMC) and between-group standardized mean differences (SMD).

Fifty-one studies met inclusion criteria, with 19 included in quantitative synthesis. OT was associated with improvement in olfactory-specific QOL (Questionnaire of Olfactory Disorders [QOD] SMC = 1.29; 95% CI [0.04-2.55]). Among controlled trials, OT produced a significant advantage in QOD improvement over no-OT (QOD SMD = 0.40; 95% CI: 0.04-0.76). OT was associated with a modest improvement in global cognitive performance (Montreal Cognitive Assessment mean difference = 0.65; 95% CI [0.35, 0.94]), but no significant effect was observed on depressive symptoms (Beck Depression Inventory SMC = -0.20; 95% CI: [-0.55, 0.14]).

OT is associated with improved olfactory-specific QOL and cognitive benefits. These findings support the potential of OT as a low-cost intervention to support the multifaceted challenges experienced by individuals with OD, while highlighting the need for adequately powered studies to clarify its effectiveness for treating OD-associated depression.