Subjective olfactory impairment (self-reported smell loss) is consistently associated with a higher likelihood of depression, whereas objectively measured olfactory impairment is more strongly linked to depression in older adults and individuals with complete smell loss. This systematic review and meta-analysis included 23 population-based studies representing 17 independent cohorts and 187,056 adults (mean age 63.6 years, 63% women). Self-reported olfactory impairment was associated with a 56% higher odds of depression (OR 1.56), and the association remained robust in studies with low risk of bias, across age groups, and regardless of whether depression was assessed subjectively or objectively. Objectively measured olfactory impairment was associated with objective depression (OR 1.26), although this association was weakened after adjustment for publication bias. However, it remained significant among adults aged 65 years or older and those with anosmia. These findings suggest that perceived smell decline may reflect psychological or self-perception factors related to depression, while objective smell impairment may identify vulnerable subgroups in later life. Further longitudinal and mechanistic studies are needed to clarify causality and determine the clinical value of olfactory impairment as a marker of late-life depression. Source: https://jamanetwork.com/
