Serum C-Reactive Protein Is Negatively Associated With Olfactory Identification Ability in Older Adults

Olfactory deficits are common in aging and associated with several conditions linked to inflammation. A few studies suggest that increased concentration of pro-inflammatory biomarkers may be related to olfactory deficits, but these associations are understudied in population-based samples.

To investigate the association between serum concentrations of C-reactive protein (CRP) and olfactory identification level as well as rate of change in aging.

We included 1,721 participants (mean age 70.5 years; 61.9% female) with at least two olfactory assessments across the 12-year follow-up. Baseline level and change in odor identification were estimated with linear mixed models as a function of CRP levels, derived from blood plasma at baseline.

Results indicated a negative dose-response association between CRP level and odor identification scores at baseline, after adjustment for demographic, cognitive, health, and lifestyle factors. CRP levels ranging between 11 and 20 mg/L were significantly related to lower olfactory ability (β = -0.811, 95% confidence interval [CI] [-1.503 to -0.118]; p = .022). Likewise, CRP values above 20 mg/L were related to lower olfactory scores, an association that approached statistical significance (β = -0.996, 95% CI [-2.045 to 0.054]; p = .063). We found no associations between CRP and olfactory change (ps > .368). Sensitivity analyses showed that associations between CRP and olfaction were confined to younger participants (age ≤72 years) and men (ps < .034).

Our findings suggest a negative association between serum CRP levels and olfactory identification ability in aging that may be dependent on age and sex.