Poor olfaction and pneumonia hospitalisation among community-dwelling older adults: a cohort study

Background: Poor olfaction is common in older adults and might signify broader health implications beyond its role in neurodegeneration. We aimed to evaluate the association of poor olfaction and the risk of any, first-ever, and recurrent pneumonia hospitalisation, as well as death due to pneumonia, in a biracial, community-based cohort of older adults. Methods: For this cohort study, we included participants from the Health, Aging and Body Composition study who were followed up with annual clinic or home visits and semi-annual or quarterly telephone interviews. These individuals completed an olfaction test using the Brief Smell Identification Test (B-SIT) in 1999–2000. Olfaction was defined as good (test score 11–12), moderate (9–10), or poor (0–8). Participants were followed up from baseline until the date of pneumonia hospitalisation, death, last contact, or the end of 13 years of follow-up, whichever came first. We excluded participants who had missing B-SIT scores or missing covariate data from our primary analysis. The primary outcome was total and first-ever hospitalisation due to pneumonia. Findings: 2494 participants aged 71–82 years (mean 75·6 years, SD 2·8) were included in our primary analysis; 1207 (48·4%) were men, 1287 (51·6%) were women; 956 (38·3%) were Black, and 1538 (61·7%) were White. During a median of 12·1 years (IQR 7·4–13·0) of follow-up, we identified a total of 801 hospitalisations due to pneumonia from 537 (21·5%) participants. Of these, 357 (66·5%) had their first-ever event during follow-up. After accounting for potential confounding from demographics, lifestyle factors, health-related conditions, and the competing risk of death, participants with poor olfaction had a higher rate of total pneumonia hospitalisations than that of those with good olfaction (intensity ratio [IR] 1·46, 95% CI 1·22–1·75; p<0·0001). Additionally, poor olfaction was associated with a higher rate for first-ever pneumonia hospitalisation (hazard ratio [HR] 1·37, 95% CI 1·06–1·79; p=0·019). Moderate olfaction was not associated with a higher rate of total (IR 1·05, 0·87–1·26; p=0·62) or first-ever pneumonia hospitalisation (HR 0·97, 0·74–1·26; p=0·79). Results were similar across sex or race subgroups. Interpretation: To our knowledge, this study provides the first epidemiological evidence that poor olfaction is associated with a long-term higher risk of pneumonia in older adults. Future studies should independently confirm this observation, investigate potential mechanisms, and understand its implications for the health of older adults. Funding: Michigan State University.