The relationship between lung function and cognitive impairment among middle-aged and older adults: The mediating role of depressive symptoms.

Background: To date, the mechanisms underlying the relationship between lung function and cognitive decline remain poorly understood. This study aims to investigate the mediating effect of depression in the longitudinal association between lung function and subsequent cognitive impairment (CI).

Methods: In the China Health and Retirement Longitudinal Study (CHARLS), a total of 7275 participants were included in the final analysis. Lung function was evaluated using peak expiratory flow (PEF) measured by a peak flow meter. A composite cognitive score was used to assess cognitive function. Linear and logistic regression models, along with bootstrap analyses, were used to investigate the mediating effect of depressive symptoms on the relationship between lung function and cognitive decline.

Results: After adjusting for potential covariates, scores on both overall cognition and its four dimensions demonstrated an increasing trend from quartile 1 (Q1) to quartile 4 (Q4) of PEF and PEF% predicted (p < 0.001). Higher PEF values (Q4 vs Q1: OR = 0.93, 95 % CI 0.90 to 0.97, p = 0.001) as well as elevated PEF% predicted (Q4 vs Q1: OR = 0.94, 95 % CI 0.90 to 0.97, p = 0.001) were associated with a reduced risk of developing CI onset. The mediation effect of depression accounted for approximately 8.2 % of the total effect concerning lung function's impact on cognitive decline.

Conclusion: Higher PEF was associated with a slower rate of longitudinal cognitive decline in middle-aged and older adults. Although depressive symptoms acted as a mediator associated with the development of CI, the majority of variance remained unexplained.