Pneumonia and subsequent risk of dementia: evidence from the Japan Gerontological evaluation study

Background Recently, several studies reported that pneumonia might increase the risk of cognitive decline and dementia due to increased frailty. Objectives This study aims to examine the association between a history of pneumonia and subsequent dementia risk. Methods Participants were 9952 aged 65 years or older Japanese men and women from the Japan Gerontological Evaluation Study prospective cohort study, followed up from 2013 to 2019. Dementia was identified by public long-term care insurance registration. A history of pneumonia contracted 1 year before the baseline questionnaire in 2013. A cox regression model was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for dementia risk, adjusted for potential confounding variables. We conducted competing risk analyses using a cause-specific hazard model. Results During the follow-up period of 6 years, 939 persons developed dementia. There was no association between having a prior history of pneumonia with dementia risk (HR 1.20, 95% CI:0.81–1.78). However, we observed an increased risk of dementia in persons with pre-frailty and frailty; the multivariable HR (95% CI) was 1.75 (1.48–2.07) and 2.42 (2.00–2.93) for pre-frailty and frailty, respectively. When pneumonia and frailty were combined, the risk of dementia was the highest for the persons with a history of pneumonia and frailty; the multivariable HR (95% CI) was 2.30 (1.47–3.62). The multivariable HR (95% CI) for those without pneumonia with frailty was 1.95 (1.66–2.28). Meanwhile, the multivariable HR (95% CI) for those with pneumonia without frailty was 1.64 (0.68–3.99). Conclusion Our findings imply that a prior history of pre-frailty and frailty with or without pneumonia, but not a history of pneumonia per se, was associated with an increased risk of dementia among population-based-cohort of older Japanese people.