Olfaction and incident Parkinson disease in US white and black older adults

To investigate olfaction in relation to incident Parkinson disease (PD) in US white and black older adults.

The study included 1,510 white (mean age 75.6 years) and 952 black (75.4 years) participants of the Health, Aging, and Body Composition study. We evaluated the olfaction of study participants with the Brief Smell Identification Test (BSIT) in 1999-2000. We retrospectively adjudicated PD cases identified through August 31, 2012, using multiple data sources. We used multivariable Cox models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

During an average of 9.8 years of follow-up, we identified a total of 42 incident PD cases, including 30 white and 12 black participants. Overall, poor sense of smell, as indicated by a lower BSIT score, was associated with higher risk of PD. Compared with the highest tertile of BSIT (t3), the HR was 1.3 (95% CI 0.5-3.6) for the second tertile (t2) and 4.8 (95% CI 2.0-11.2) for the lowest tertile (t1) (p_trend < 0.00001). Further analyses revealed significant associations for incident PD in both the first 5 years of follow-up (HR_t1/[t2+t3] 4.2, 95% CI 1.7-10.8) and thereafter (HR_t1/[t2+t3] 4.1, 95% CI 1.7-9.8). This association appeared to be stronger in white (HR_t1/[t2+t3] 4.9, 95% CI 2.3-10.5) than in black participants (HR_t1/[t2+t3] 2.5, 95% CI 0.8-8.1), and in men (HR_t1/[t2+t3] 5.4, 95% CI 2.3-12.9) than in women (HR_t1/[t2+t3] 2.9, 95% CI 1.1-7.8).

Poor olfaction predicts PD in short and intermediate terms; the possibility of stronger associations among men and white participants warrants further investigation.