Associations of Lung Function Decline with Risks of Cognitive Impairment and Dementia: A Meta-Analysis and Systematic Review

Background: There are controversies surrounding the effects of lung function decline on cognitive impairment and dementia. Objective: We conducted a meta-analysis and systematic review to explore the associations of lung function decline with the risks of cognitive impairment and dementia. Methods: The PubMed, EMBASE, and the Cochrane Library were searched to identify prospective studies published from database inception through January 10, 2023. We pooled relative risk (RR) and 95% confidence intervals (CI) using random-effects models. The Egger test, funnel plots, meta-regression, sensitivity, and subgroup analyses were conducted to detect publication bias and investigate the source of heterogeneity. Results: Thirty-three articles with a total of 8,816,992 participants were subjected to meta-analysis. Poorer pulmonary function was associated with an increased risk of dementia (FEV: RR= 1.25 [95%CI, 1.17-1.33]; FVC: RR= 1.40 [95%CI, 1.16-1.69]; PEF: RR= 1.84 [95%CI, 1.37-2.46]). The results of the subgroup analyses were similar to the primary results. Individuals with lung diseases had a higher combined risk of dementia and cognitive impairment (RR = 1.39 [95%CI, 1.20-1.61]). Lung disease conferred an elevated risk of cognitive impairment (RR = 1.37 [95%CI, 1.14-1.65]). The relationship between lung disease and an increased risk of dementia was only shown in total study participants (RR = 1.32 [95%CI, 1.11-1.57]), but not in the participants with Alzheimer's disease (RR = 1.39 [95%CI, 1.00-1.93]) or vascular dementia (RR = 2.11 [95%CI, 0.57-7.83]). Conclusion: Lung function decline was significantly associated with higher risks of cognitive impairment and dementia. These findings might provide implications for the prevention of cognitive disorders and the promotion of brain health.