Interactions of physical activity and lung function on cognitive health in older adults: Joint association and mediation analysis.

Background: Maintaining cognitive health in old adults has become a significant public health challenge, with lung function and physical activity (PA) as essential modifiable factors. However, the joint and mediation effects of these two factors with cognition remain unclear.

Objectives: This study assesses the joint association and mediation effects of lung function and PA with cognition.

Design, setting, and participants: We utilized cross-sectional data from the 2011-2012 U.S. National Health and Nutrition Examination Survey, including adults aged 60-79 assessed for lung function, PA, and cognition.

Main outcomes and measures: Lung function included forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), peak expiratory flow (PEF) and FEV₁/FVC. PA was assessed using the Global Physical Activity Questionnaire, covering occupational PA (OPA), transportation-related PA (TPA), and leisure-time PA (LTPA). Cognition was evaluated using the Digit Symbol Substitution Test, Animal Fluency Test, Delayed Recall Test and Immediate Recall Test. Weighted multiple linear regression models were used to analyze the separate and joint associations of lung function and PA with cognition, while also exploring potential mediation effects between these factors.

Results: A total of 927 participants, representing 35,525,782 U.S. residents, were included, with a weighted median age of 65 (IQR, 63 -71) years, and 53.6 % were female. The results showed a significant positive association between lung function and cognitive function, with FEV₁, FVC, and PEF all positively correlated, while the FEV₁/FVC showed no notable link. Further analysis revealed the best cognitive performance observed in participants with active LTPA and the highest quartile of lung function, indicating a joint association of LTPA and lung function with cognition. Mediation analysis indicated that lung function mediated 24.1 % (95 %CI: 6.3 % - 47.0 %, P = 0.03) of the relationship between LTPA and cognition, while cognition mediated 10.2 % (95 %CI: 0.5 % - 27.0 %, P = 0.04) of the relationship between LTPA and lung function.

Conclusion: Lung function and cognition may have a bidirectional relationship. The combination of active LTPA and better lung function was strongly associated with higher cognition, highlighting the need to strengthen exercise focused on lung function to maintain cognitive health in older adults.