An analysis of longitudinal data from the English Longitudinal Study of Ageing (ELSA) found an association between lung function and cognitive impairment in older people over an average follow-up period of 12 years1.
"Cross-sectional studies suggest that lung function may be a risk factor for cognitive deterioration and dementia in the older population. However, the evidence from longitudinal studies remains inconsistent," said Dr. Yutong Cai (University of Oxford, UK) describing the background to this cohort study. The research team, therefore, investigated the possibility of a link between lung function and cognitive decline over time.
They included 6,107 subjects in the ELSA study, whose baseline data contained complete information on cognitive function. All participants had at least one cognition reassessment between 2006/2007 and 2016/2017. The tests consisted of an assessment of global cognitive abilities as well as memory, executive functions, and their sense of orientation. The individual test results were transferred to a z score. A global z-score was determined by calculating the test-specific z-score and tracing it back to the global z-score of the baseline. The lung function parameters at baseline consisted of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF).
The baseline data from continuous FEV1 measurements were used together with FEV1 quartiles for both men and women. A linear mixed model was used to assess an association between lung function at baseline and gradual loss of cognitive function, taking into account possible confounding factors such as age, education, weight, marital status, depression symptoms, physical activity, alcohol consumption, smoking, and diagnoses such as diabetes, hypertension, chronic bronchitis or emphysema, coronary heart disease, stroke, and cancer.
The results of the 12-year follow-up showed a clear association between FEV1, FVC, and PEF with a decrease in all measured dimensions of cognitive function for both sexes in the older study population (P<0.001). "Very interestingly, we found that this correlation was particularly strong in women compared to men," Dr. Cai emphasized.
Looking at the global cognitive z scores, the multivariable-adjusted changes associated with a decrease in FEV1 per 1L were -0.041 standard deviation (SD)/year (P<0.001) in women and -0.019 SD/year (P<0.001) in men. Regarding the mean differences in the rate of change in z scores for memory, the research team found values of -0.046 and -0.031 (both for quartile 1; P<0.001) for women and men. "The results show a clear correlation: if there was lower lung function at the beginning of the study, there was a faster decline in cognitive function," Dr. Cai summarised.
1. Cai Y, et al Reduced lung function and cognitive decline in ageing: a longitudinal cohort study. Abstract and e-poster 4186, ERS International Virtual Congress 2020, 7-9 Sept.