Effects of Olfactory Training on Olfactory and Cognitive Function: A Systematic Review.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis containing randomized controlled trials
PubMed 41093804 · doi:10.1177/01455613251384121
What was done
A systematic review and meta-analysis following PRISMA guidelines was conducted across PubMed, Embase, Web of Science, and Cochrane databases. The authors evaluated the effects of olfactory training (OT) on olfaction, cognition, and neuroimaging outcomes across healthy adults, individuals with olfactory dysfunction, and patients with cognitive impairment. A total of 24 full-text studies (12 randomized controlled trials [RCTs] and 12 non-RCTs) were analyzed, with intervention durations typically spanning 3 to 6 months.
What was found
In healthy adults (6 studies) and adults with olfactory dysfunction (13 studies), OT improved olfactory function and showed domain-specific cognitive benefits in global cognition, verbal fluency, and working memory. Meta-analysis showed that 27.01% of individuals (95% CI, 0.16–0.40) achieved clinically significant olfactory improvement. In adults with cognitive impairment (5 studies), standard OT had limited effects, but intensive OT (enriched odors, longer sessions) showed potential benefits. Neuroimaging studies reported increased brain volumes in multiple regions and neuronal reorganization.
Why it matters
This review synthesizes evidence showing that structured sensory olfactory input may stimulate neuroplasticity and improve specific cognitive domains, particularly in cognitively intact individuals or those with primary olfactory loss.
Limits
The primary limitation is the low methodological quality of the included literature: 7 of 12 RCTs had a high risk of bias, and 11 of 12 non-RCTs had serious bias. The abstract does not report total participant numbers, effect sizes, or confidence intervals for cognitive or neuroimaging outcomes. Standard OT protocols showed limited efficacy in populations with established cognitive impairment.
Cited by
- supports Smell training protocols involving repeated deliberate sniffing of specific odors can improve olfactory acuity and assist recovery after olfactory loss or injury.