Association Of Sleep Duration And Sleep Quality With Cognitive Function In Middle-aged And Elderly People

With the development of global aging,the burden of disease among middle-aged and elderly people have gradually become a major issue in the field of public health.Studies have shown that among the burden of diseases caused by chronic diseases in the elderly,the disability-adjusted life years(DALYs)caused by dementia could account for11.9%of all diseases.Cognitive function declines to varying degrees with age growth,and the prevalence and incidence of cognitive impairment will continue to increase.According to the 2015 Global Alzheimer’s Disease Report,there were about 47 million dementia patients worldwide in 2015,which will reach 75 million in 2030.In China,the number of dementia patients was nearly 9.5 million in 2015,accounting for about 20%in the world,and it is expected to exceed 16 million in 2030.Cognitive impairment is an important manifestation of dementia.Identifying and discovering the risk factors affecting cognitive function and adopting early intervention are of great public health significance for delaying or preventing the occurrence of dementia in the middle-aged and elderly population.Cognitive impairment includes mild cognitive impairment(MCI)and dementia,caused by a variety of factors.Studies found that in addition to unalterable factors,unhealthy lifestyles such as smoking,alcohol consumption and obesity also affected cognitive impairment.Sleep,an essential physiological activity,supporting all major physiological systems of the body and playing a crucial role in the development of cognitive function in the whole life.A series of changes on sleep occurred after aging,such as reduced sleep duration,low sleep efficiency,poor sleep quality,difficulty in falling asleep,excessive daytime sleepiness.Study statistics show that about 50%of the elderly suffered from sleep problems.As an unhealthy behavior that affects the quality of life in middle-aged and elderly adults,sleep disturbance and its effect on cognitive function is worthy of further study.To explore the effects of sleep duration and sleep quality on cognitive function in middle-aged and elderly adults.In this study,a cross-sectional study was conducted to analyze the association of nighttime sleep duration,nap duration and sleep quality with cognitive function in middle-aged and elderly adults.Meanwhile,comparing the change of nighttime sleep duration and nap duration of subjects during a 6-years period,and exploring their effects on cognitive function.Objective:Exploring the correlation between sleep factors(nighttime sleep duration,nap duration and sleep quality)and cognitive function in middle-aged and elderly people,and to provide some basis for studying the factors affecting cognitive function.Methods:Based on the Dongfeng-Tongji cohort,3292 retired employees were randomly recruited to conduct a questionnaire survey,excluded 19 self-reported patients with Parkinson’s disease,and finally 3273 subjects were included.General demographic characteristics[gender,age,Body mass index(BMI),marital status,education level],lifestyle[smoking status,drinking status,sleep status(including nighttime sleep duration,nap duration),physical exercise]and disease history(hypertension,diabetes mellitus,cardiovascular disease,tumor)of the subjects were collected by face-to-face questionnaires.In addition,sleep quality was evaluated by Pittsburgh sleep quality index(PSQI),and good sleep quality ware determined by PSQI≤5,poor sleep quality were determined by PSQI>5.Cognitive function of the subjects were evaluated by Mini-mental state examination(MMSE),and the mild cognitive impairment(MCI)were defined as an MMSE score of less than 20 points for those with an elementary school education or less or less than 24 points for those with a middle school education or higher.Using multivariate generalized linear regression to analyze the association of nighttime sleep duration,nap duration and sleep quality with the MMSE score in middle-aged and elderly adults,with adjustments for age,gender,BMI,marital status,education level,smoking status,drinking status,physical exercise and history of disease(hypertension,diabetes mellitus,cardiovascular disease,tumor).And multivariate Logistic regression model was used to analyze the association of nighttime sleep duration,nap duration and sleep quality with MCI in middle-aged and elderly people(adjusting the above factors).Besides,we investigated the effects of nighttime sleep duration,nap duration and sleep quality on MMSE score and the risk of MCI among different subgroups,classifying total population by age(<65 and≥65 years old),gender(males and females),smoking status(never smokers and ever smokers),alcohol drinking status(never drinkers and ever drinkers),BMI(<25kg/m2and≥25kg/m2),respectively.Moreover,the combined effects of nighttime sleep duration and nap duration,sleep quality on MMSE score and the risk of MCI were investigated.Furthemore,since 2532 of the 3273 subjects participated in the Dongfeng-Tongji cohort in 2013,information on nighttime sleep duration and nap duration in 2013 was provided.Using multivariate generalized linear regression and multivariate Logistic regression model to analyze the impact of changes in nighttime sleep duration and nap duration between 2013 and 2019 on MMSE scores and the risk of MCI,with adjustments for age,gender,BMI,marital status,education level,smoking status,drinking status,physical exercise and history of disease(hypertension,diabetes mellitus,cardiovascular disease,tumor).Results:In a cross-sectional analysis,MMSE scores were significantly lower in subjects sleeping≥9 hours/night compared to those who sleeping[7-8)hours/night(24.7±4.4 vs.26.3±3.3,P<0.001),the MMSE scores of no nap were significantly lower than those who napped within half an hour([1-30]minutes)(25.5±3.7 vs.26.3±3.3,P<0.001),and poor sleepers had lower MMSE scores than good sleepers(25.4±3.6 vs.25.9±3.5,P=0.001).Compared with those who sleeping[7-8)hours/night,the MMSE scores were significantly lower[βand 95%Confidence intervals(CI)were-1.338(-1.705,-0.971),P<0.001]and had a greater risk of MCI[OR(95%CI)=2.12(1.49,3.01),P<0.001]for those who sleeping≥9 hours/night,and the effect exsits in different ages(<65 and≥65 years old),different genders(male,female),different smoking status(never smokers,ever smokers),different drinking status(never drinkers,ever drinkers),and different BMI groups(<25kg/m~2,≥25kg/m~2)of stratified analysis.The MMSE scores of those who did not nap were significantly lower than those who napped for less than half an hour[β(95%CI)=-0.413(-0.713,-0.112),P<0.001],and those effect was mainly observed in age≥65[-0.469(-0.862,-0.076)],female[-0.417(-0.788,-0.045)],never smokers[-0.454(-0.786,-0.121)],never drinkers[-0.521(-0.856,-0.186)]and BMI<25kg/m~2[-0.370(-0.720,-0.021)]in the stratification analysis.The MMSE scores were significantly lower in those with poor sleep quality than in those with good sleep quality[β(95%CI)=-0.516(-0.771,-0.261),P<0.001],and the effect exsits in age<65[-0.581(-0.969,-0.193)],female[-0.643(-0.967,-0.319)],ever smokers[-0.693(-1.246,-0.140)],never drinkers[-0.526(-0.816,-0.235)]and BMI≥25kg/m~2[-0.639(-1.097,-0.182)].In addition,we used those who took a nap of less than half an hour and those who had good sleep quality as reference,respectively,and found no statistically significant association between nap duration and sleep quality and the risk of MCI.Moreover,to assess the combined effects of nighttime sleep duration and nap duration,sleep quality on cognitive function,we found that compared with those who sleeping[7-8)hours/night and napping[1-30]minutes,people who sleeping≥9hours/night and no napping had significantly lower MMSE scores[β(95%CI)=-1.546(-2.23,-0.861),P<0.001];and people who sleeping≥9 hours/night and napping[31-60]minutes had significantly lower MMSE scores[β(95%CI)=-1.569(-2.29,-0.849),P<0.001]and higher risk of MCI[OR(95%CI)=2.05(1.01,4.13),P<0.001].Comparing with those who sleeping[7-8)hours/night and had good sleep quality,the lowest MMSE score[β(95%CI)=-1.652(-2.286,-1.017),P<0.001]and the highest risk of MCI[OR(95%CI)=2.29(1.31,4.01),P=0.002]were observed in those who sleeping≥9 hours/night and had poor sleep quality.Furthermore,we explored the effects of changes in nighttime sleep duration and nap duration on cognitive function over a 6-year period,with 2532 subjects providing information on nighttime sleep duration and nap duration in 2013 and 2019.Our study found that the MMSE scores of people whose nighttime sleep duration increased from<7,[7-8)and[8-9)hours to≥9 hours,and those whose nighttime sleep duration sustaining at≥9 hours were significantly lower than subjects who maintained[7-8)hours/night in both 2013 and 2019.[βand 95%CI were-2.979(-4.777,-1.181),-1.659(-2.872,-0.446),-1.050(-2.041,-0.059)and-1.773(-2.780,-0.765),respectively,all P values<0.05];and the MMSE scores were significantly lower in subjects whose nighttime sleep duration decreased from[8-9)h to<7 h,≥9 h to<7,[7-8)and[8-9)h[βand 95%CI were-1.154(-2.003,-0.305),-2.572(-3.758,-1.385),-1.552(-2.550,-0.554)and-1.101(-1.862,-0.339)respectively,all P values<0.05].Moreover,subjects whose nighttime sleep duration increased from<7,[7-8)and[8-9)hours/night to≥9hours/night had a significantly increased risk of MCI compared with subjects whose nighttime sleep duration was maintained at[7-8)hours/night[OR and 95%CI were 5.51(1.70,17.87),2.71(1.11,6.62),2.37(1.13,4.98),all P values<0.05],and the risk of MCI was 2.11-fold[(OR(95%CI)=3.11(1.52,6.37),P=0.002]increased in those who sleeping≥9 hours/night stably compared to whose nighttime sleep duration was maintained at[7-8]hours/night.The effects of the change of nap duration on cognitive function are mainly shown as follows:compared to those who napping remained within half an hour([1-30]minutes),the MMSE scores of those who napping from 0 minutes to 60 minutes were significantly lower[β(95%CI)=-1.421(-2.316,-0.525),P=0.002];napping within an hour([1-30]or[31-60]minutes)changed to no napping and long-term no napping with significantly lower MMSE scores as well.And the risk of MCI increased by 1.22-fold in the group whose nap duration varied from[31-60]minutes to no napping,compared with those whose nap duration maintained within half an hour.Conclusions:In middle-aged and elderly people,compared with subjects sleeping[7-8]hours/night,subjects sleeping≥9 hours/night had a lower MMSE score and an increased risk of MCI.And no napping had lower MMSE scores than those who napped for less than half an hour,subjects with poor sleep quality had lower MMSE scores than those with good sleep quality.Compared with subjects who sleeping[7-8)hours/night and had good sleep quality,those who sleeping≥9 hours/night and had poor sleep quality had the lowest MMSE score and the highest risk of MCI.Compared with subjects whose nighttime sleep duration was maintained at[7-8)hours,those who sleeping increased from<9 hours to≥9 hours,and nighttime sleep duration sustaining at≥9 hours,their MMSE score was significantly reduced and the risk of MCI was significantly increased.Subjects whose nap duration changed from[31-60]minutes to 0minute,compared with the group whose nap duration was less than half an hour,the MMSE score decreased and the risk of MCI increased.Our results show that maintaining a stable and moderate sleep duration[sleeping[7-8)hours/night,napping within half an hour]and ensuring good sleep quality are beneficial to the development of cognitive function in middle-aged and elderly people.This study provides some epidemiological evidence for revealing the effect of sleep factors on cognitive function in middle-aged and elderly population,but the tangible biological mechanism needs further studied.