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Olfactory dysfunction predicts the development of depression in older US adults.

Neuroanatomic connections link the olfactory and limbic systems potentially explaining an association between olfactory dysfunction and depression. Some previous studies have demonstrated that olfactory dysfunction is associated with increased depressive symptoms. However, these studies were cross-sectional and unable to establish which develops first. We used longitudinal data to determine if impaired odor identification increased subsequent depressive symptoms or vice versa. We assessed olfaction and depression in the National Social Life, Health, and Aging Project, a nationally-representative, 15-year longitudinal study of older U.S. adults. Olfaction was measured using a validated odor identification test (Sniffin' Sticks). Depressive symptoms were measured using a modified version of the validated Center for Epidemiological Studies Depression Scale. Multivariable logistic regression models examined the temporal relationships between developing olfactory dysfunction and depression while accounting for demographics, disease comorbidities, alcohol use, smoking, and cognition. Older adults with olfactory dysfunction had concurrent frequent depressive symptoms (OR = 1.20, 95% CI = 1.00 - 1.43). Among healthy adults at baseline, those who had olfactory dysfunction were more likely to develop frequent depressive symptoms 5 or 10 years later (OR = 2.22, 95% CI = 1.13 - 4.37). Conversely, those with frequent depressive symptoms at baseline were not more likely to develop olfactory dysfunction 5 or 10 years later. We show for the first time that olfactory dysfunction predicts subsequent development of depression in older U.S. adults. These data support screening for depression in older adults with chemosensory impairment and set the stage for disentangling the relationship between olfaction and depression.