Respiratory Disease and Lower Pulmonary Function as Risk Factors for Dementia A Systematic Review With Meta-analysis

BACKGROUND: In addition to affecting the oxygen supply to the brain, pulmonary function is a marker of multiple insults throughout life (including smoking, illness, and socioeconomic deprivation). In this meta-analysis of existing longitudinal studies, the hypothesis that lower pulmonary function and respiratory illness are linked to an elevated risk of dementia was tested. METHODS: A systematic review was conducted of longitudinal studies using PubMed until April 1, 2019, and, where possible, results were pooled in random effects meta-analyses. RESULTS: Ten studies relating pulmonary function to later dementia risk and 11 studies of respiratory illness and dementia (including one that assessed both factors) were identified. The lowest quartile of FEV1 compared with the highest was associated with a 1.4-fold (hazard ratio [HR], 1.46; 95% CI, 0.77-2.75) increased dementia risk (N-total = 62,209; two studies). A decrease of 1 SD in FEV1 was associated with a 28% increase in dementia risk (HR, 1.28; 95% CI, 1.03-1.60; N-total 67,505; six studies). Respiratory illness was also associated with increased dementia risk to a similar degree (pooled HR, 1.54; 95% CI, 1.30-1.81; N-total = 288,641; 11 studies). CONCLUSIONS: Individuals with poor pulmonary function experience an increased risk of dementia. The extent to which the association between poor pulmonary function and dementia is causal remains unclear and requires examination.