Correlation Between Sleep Disorders And Cognitive Function Among Rural-dwelling Elderly People In Shandong Province

BackgroundSleep disorders and cognitive impairments are common in the elderly.As population ages,the number of people with sleep disorders and cognitive impairment steadily increases.Epidemiological research suggests that more than one-third of elderly people suffer from the different types of sleep disorders.The total number of people with Alzheimer's disease(AD),the most common neurodegenerative disease in the elderly,increase along with population aging,which has placed a heavy burden to families,caregivers,and the society.So far,there is no effective medical treatment for AD in clinical practice.However,existing epidemiological studies show that the risk and progression of AD is determined by genetic and environmental factors and their interactions,including modifiable factors such as lifestyle,diet,physical exercise,cardiometabolic risk factors,and psychosocial factors.Growing evidence suggests that there is a potential link between sleep problems and cognitive dysfunction in older people.Observational studies suggest that insomnia,poor sleep quality,abnormal sleep duration,daytime sleepiness,and abnormal sleep-wake cycles can adversely affect cognitive function,even in the early stages of cognitive dysfunction.Experimental studies suggest that good sleep is beneficial to the clearance of toxic metabolites(e.g.,amyloid ?)in brain tissue,and studying the relationship between sleep disorders and cognitive function may provide the potential for early prevention of cognitive impairment and dementia.Epidemiological studies suggested that there were approximately 47 million AD patients worldwide in 2015 and this number was projected to reach 75 million by 2030.In 2010,the global expenditure of AD was about US$604 billion(?1.0%of global GDP),and in 2015 it increased to US$818 billion(?1.1%of global GDP).In 2010,there were about 9 million AD patients in China,and the current number of patients with AD is estimated to be more than 10 million.According to the China National Bureau of Statistics,the proportion of people aged 65 years and over in China reached 11.9%in 2018.As a large agricultural province in China,Shandong faces a huge challenge of rapid aging of rural population,and sleep disorders and cognitive dysfunction increase with advancing age.It will increase the pressure on social security and public services,and continue to affect social vitality,innovation power and potential economic growth rate.It represents a great challenge for population development in the new era.Currently,there is lacking of large-scale population-based epidemiological survey to investigate sleep and cognition among older people living in rural areas of Shandong Province.Therefore,in this study we seek to reveal the general health status of the elderly in rural areas of Shandong Province,the prevalence of sleep disorders and cognitive impairments and related risk factors.Developing an intervention program suitable for the characteristics of the rural elderly population in China will help effectively cope with increasing challenges of AD and dementia to the sustainable social and economic development.ObjectivesTo analyze the correlation between sleep disorders and cognitive impairment in elderly population in rural areas of Shandong province.Subjects and methodsFrom August to December 2014,a face-to-face epidemiological survey was conducted on 53 villages(age>65 years in Yanlou Town,Yanggu County,Liaocheng City,Shandong Province.The study population represents the“13th Five-Year Plan"national key R&D program—a major research project on prevention and control of chronic non-communicable diseases—a randomized controlled multimodal intervention study to delay dementia and disability in China(i.e.,A Randomized Controlled Multimodal Intervention to Delay Dementia and Disability in China,MIND-CHINA).The survey was approved by the ethics committee at Shandong Provincial Hospital affiliated to Shandong University in Jinan,and the consent was obtained from the respondents or their families,and written informed consent was signed.The inclusion criteria were:registered residents of Yanlou Town,Yanggu County,Shandong Province,and have resided continuously in the town for more than 1 year,and have resided locally for more than 6 months each year,and were aged 65 years or above at baseline.The exclusion criteria were:people with severe depression,schizophrenia and other mental disorders,people who cannot complete the cognitive test due to severe hearing,visual or language impairment or who refuse to sign the informed consent.The epidemiological survey was conducted in the local town hospital,and the structured questionnaire was used for interview to collect data on general social demographic characteristics such as age,occupation,marital status,smoking,drinking and other health-related behaviors,diabetes,hypertension,coronary heart disease,stroke and other diseases and other health related factors.Sleep Quality and patterns were evaluated by The Pittsburgh Sleep Quality Index(PSQI).Sleep disturbance was defined as PSQI score>7.We used multiple logistic regression models to analyze the associations between sleep disorders and various factors.The Epworth Sleepiness Scale(ESS)was used to measure daytime Sleepiness Global cognitive function was tested by using the Mini-Mental State Examination(MMSE)and the Ascertain Dementia 8-item Questionnaire(AD8).The ESS score ?14 indicates obvious daytime sleepiness tendency.The cut-off of the MMSE score for abnormality(i.e.,cognitive impairment)is based on education level:the MMSE score?17 points for illiteracy group,?20 points for primary school(education?6 years),and-24 points for middle school or above(education>6 years).Followed up the group in 2018,and the cognitive function was evaluated by MMSE.The cognitive function changes in the normal sleep group and the sleep disorder group,and the non-daytime sleepiness group and the daytime sleepiness group were analyzed,and the correlation between sleep abnormalities and cognitive dysfunction was further analyzed.Results1.Sociodemographic characteristics of the study participantsOf the 2195 participants,the mean age was 71.67 years(SD,5.89),and women accounted for 57.9%.The education level of the elderly in this rural area was low,and the illiterate and primary education level accounted for the majority.Nearly 1/3 of the populations had the habits of smoking and alcohol drinking,and diabetes,hypertension,and coronary heart disease were common among participants.2.Prevalence and associated factors of sleep disorders defined by PSQI scale(1)The overall prevalence of sleep disorders was 33.8%,with the prevalence being 39.2%for women and 26.3%for men(P<0.001).(2)The group with sleep disorders was older than the normal sleep group,had a low level of education,and had a high proportion of hypertension,diabetes,hyperlipidemia,coronary heart disease,chronic obstructive pulmonary disease,and stroke.(3)The most common types of sleep disorders in the population were increased sleep latency(39.7%),shorter sleep time(31.0%),and reduced sleep efficiency(28.8%)(4)In the PSQI subdomains,the decrease of sleep efficiency tends to decrease with increasing age(P<0.001).(5)The prevalence rates of sleep disorders in all subdomains were higher in women than in men,and there were statistical differences in difficulty falling asleep,abnormal sleep time,decreased sleep efficiency,and daytime dysfunction(P<0.001).(6)Risk factors associated with sleep disorders:multiple logistic regression analysis suggested that sleep disorders were significantly associated with women(OR=1.76,95%CI 1.46-2.12),hypertension(OR=1.28,95%CI 1.06-1.54),coronary heart disease(OR=1.60,95%CI 1.27-2.00),and chronic obstructive pulmonary disease(OR=1.82,95%CI 1.34-2.49).3.Sleep disorders and cognitive function(1)After adjusting for educational level,the rate of abnormal MMSE scor e(i.e.cognitive impairment)was 32.7%,nearly one-third of the participants.(2)Based on PSQI score,the rate of abnormal MMSE score in the sleep disorder group was higher than that in the normal sleep group(35.8%vs.31.1%,P<0.028);AD8 scores were higher in the sleep disorder group than thos e in the normal sleep group(2.30±1.6 vs.1.63± 1.6,P<0.001).(3)Out of the 7 subdomains of PSQI,except sleep duration,the scores of the 6 other PSQI subdomains were higher in the cognitive impairment group than those of the normal cognitive functional group,and the differences between the groups in the subdomains of falling asleep,sleep quality,sleep efficiency,and daytime dysfunction were statistically significant(P<0.008-0.001)(4)The scores in time orientation,spatial orientation,immediate memory,attention and calculation,delayed recall,naming and language ability,repeat,reading,language comprehension,writing,and visual space were lower in the sleep disorder group than those in the normal sleep group,and the scores in cognitive domains of time orientation,immediate memory,attention,and computing power,naming,repetition,reading,writing and visual space were significantly different between the two groups(P<0.029-0.001).4.Daytime sleepiness and cognitive function(1)The rate of cognitive impairment was higher in the daytime sleepiness group than that in the non-daytime sleepiness group(32.5%vs.31.7%,P<0.005),and the AD 8 score in the daytime sleepiness group was higher than that in the non-daytime sleepiness group(2.85± 1.9 vs.1.80 ± 1.6,P<0.001).(2)The scores in time orientation,spatial orientation,immediate memory,attention and calculation,delayed recall,naming and language ability,repetition,reading,language comprehension,writing,and visual space were all lower in the daytime sleepiness group than those without daytime sleepiness.There were statistical differences in time orientation,attention and calculation,naming,repetition,and visual space(P<0.036-0.001)5.Risk factors of cognitive dysfunction:Logistic regression analysis found that female,older age,low educational level,and stroke were correlated with cognitive dysfunction.After adjusting for the above demographic and sociological factors,cognitive impairment was significantly correlated with daytime dysfunction in PSQI(OR=1.356,95%CI 1.089-1.690)and daytime sleepiness(OR=1.871,95%CI 1.269-2.759).6.Changes of cognitive function and correlation analysis in population follow-upAfter 4 years,the MMSE examination was performed to assess the changes in cognitive function.The results suggested that the normal sleep group(22.47±5.38 vs.20.59±6.15),the sleep disorder group(21.31±5.22 vs.19.60±5.98),the non-daytime sleepiness group(22.19±5.31 vs.20.31±6.36)and the daytime sleepiness group(20.61±5.93 vs.19.60±6.40)were all lower than the baseline level,and the difference was statistically significant(P<0.001).After adjusting for socio-demographic factors,there was no significant correlation between sleep disorders and cognitive impairment,,while daytime sleepiness was still related to cognitive impairment,and no daytime sleepiness was a protective factor for cognitive function(OR=0.633,95%Cl 0.402-0.988).Conclusion1.The prevalence of chronic diseases among the elderly in this rural area of Shandong province is relatively high.2.There is a high prevalence of sleep disorders among the rural elderly in Shandong province.Certain modifiable risk factors,such as cardiometabolic risk factors,are associated with poor sleep quality,which may be potential targets for interventions to improve the quality of sleep among the rural-dwelling elderly people.3.The prevalence of cognitive impairment among older people in this rural region is relatively high,which affects nearly one-third of the elderly.4.Daytime sleepiness may be independently related to the risk of cognitive impairment in the elderly.Identifying abnormal daytime sleepiness has important public health significance,as daytime sleepiness may be an early marker of cognitive decline and the progression to the onset of dementia and a potential reversible risk factor.