Association Between Lung Function And The Long-term Change In Cognition Among Middle-aged And Older Adults

Aim:With the rapid development of the aging population,the health of elderly has become a major issue worldwide.Cognitive impairment is one of the leading problems endangering the health of the elderly in recent years.Several studies generally suggest that age-related cognitive impairment is irreversible.Cognitive impairment is related to a series of adverse health outcomes,which seriously threatens the independence and quality of life in the elderly,and brings heavy disease and economic burden to the society.The predictive value of lung function for cognitive performance later in life had been reported by some previous prospective studies.However,few literatures have taken the effect of lung function on the long-term change trajectory of quantitative cognition into account.It is less clear that if poor lung function accelerates cognitive decline in normal aging.Accordingly,we conducted a large-sample prospective study to explore the effect of baseline lung function on the long-term change in cognition among middle-aged and older adults,providing scientific and effective measures for the prevention and intervention of cognitive impairment and dementia.Methods:Data were from the English Longitudinal Study of Ageing（ELSA,2004～2010）.ELSA is an on-going prospective and nationally representative cohort of the community-dwelling people aged 50 and over.Participants were followed up every 2years using computer-assisted personal interviews and self-completion questionnaires,with additional nurse visits every 4 years for the assessment of biomarkers.At present,a total of 8 panel waves have been conducted in ELSA（2002～2016/17）.This study investigated participants from wave 2 to wave 5,spanning a time of 6 years.Lung function including forced expiratory volume in 1 s（FEV1）and forced vital capacity（FVC）were measured by using a hand-held vitalograph spirometer at wave 2（baseline in this study）.FEV1 or FVC was divided by height squared（m²）to obtain a measure that was adjusted for body size.Then,based on the age（per 10 years）-and sex-specific median for FEV1/FVC,participants were eventually divided into two groups,i.e.low FEV1 vs.high FEV1 or low FVC vs.high FVC.Cognition including time orientation,word-list recall,verbal fluency and letter cancellation were assessed using a battery of tests at Wave 2,3,4and 5.Generalized estimating equation（GEE）models were used to test the associations between baseline lung function and four visits of cognition.The time variable was interacted with FEV1 or FVC category to identify the effects of lung function on the change of cognition overtime.All of the GEE models were adjusted for the potential confounders:age,gender,education,body mass index（BMI）,smoking,alcohol intake,physical activity,cardiovascular diseases（including angina,congestive heart failure and stroke）,hypertension,diabetes,chronic lung diseases,Parkinson,dementia,cancer and depression at baseline.Results:A total of 6,080 participants aged 50 years or over were eligible for this study,including 2,758 males and 3,322 females.The median of follow-up time was 6 years.At baseline,the mean scores of time orientation,word-list recall,verbal fluency and letter cancellation were 3.81±0.44,10.72±3.15,21.07±6.21 and 19.31±5.47,respectively.At the fourth panel survey,the scores were 3.74±0.62,10.28±3.67,20.59±6.79 and 18.51±5.32,respectively.The cognition showed a downward trend.The GEE results showed that compared to participants with higher lung function,those who had lower lung function at baseline experienced a faster rate of decline in time orientation(joint test:χ²_interaction=9.49,df=3,P=0.023 for FVC),word-list recall(joint test:χ²_interaction=12.07,df=3,P=0.007 for FVC),and verbal fluency(joint test:χ²_interaction=9.13,df=3,P=0.028 for FEV1 and joint test:χ²_interaction=12.76,df=3,P=0.005 for FVC).No association was found between baseline lung function and the rate of decline in letter cancellation(joint test:χ²_interaction=1.29,df=3,P=0.733 for FEV1 and joint test:χ²_interaction=2.35,df=3,P=0.503 for FVC).Sensitivity analysis excluding participants who reported dementia,cardiovascular diseases,chronic lung diseases and cancer showed that the results of this study were relatively stable and high reliability.Conclusions:Lower baseline lung function was associated with worse cognitive performance in later life.Compared to participants with better lung function,those who had poor FEV1 or FVC at baseline have faster rate of decline in time orientation,word-list recall and verbal fluency among middle-aged and older adults.This study provides the additional evidence that better lung function earlier in life plays an important role in preventing the cognitive decline during ageing.