Association Between Cognitive Impairment And Decline On The All-cause Mortality Among The Oldest Old In China

ObjectTo explore the effects of cognitive impairment and cognitive decline on all-cause mortality in the oldest old,and to explore the differences between the oldest old in different age groups(80-89 years old and ?90 years old)and sex(male and female).The purpose of this study is to assess the impact of cognitive functioning of the oldest old on later life expectancy,to formulate future public health policies and provide high-quality health services as an important reference.MethodsThe data in this study were obtained from the Chinese Longitudinal Healthy Longevity Survey(CLHLS),which randomly selected about half of cities and counties in 23 provinces(cities and autonomous regions)in China.The survey project conducted a baseline survey in 1998,and then conducted follow-up surveys in 2000,2002,2005,2008-2009,2011-2012,and 2014.Seven follow-up surveys included a total of 43287 elderly people.The cognitive function was measured by Mini-Mental State Examination(MMSE).(1)The cognitive function was divided into four dividing points:severe cognitive impairment(0-17 points),moderate cognitive impairment(18-23points),mild cognitive function(24-27 points)and normal cognitive function(28-30points).(2)According to the education level-the cut-off points of cognitive impairment were used-the oldest old with MMSE < 18 and no education were judged to becognitive impairment-the oldest old with MMSE < 21 and education for 1-6 years were judged to be cognitive impairment-and the oldest old with MMSE < 25 and education for more than 6 years were judged to be cognitive impairment.(3)cognitive function was tested twice,and cognitive decline was defined as a decline from baseline to the next follow-up to the lower MMSE category.Chi-square test was used to compare the differences of classification variables and ANOVA was used to compare the differences of continuity variables.Kaplan-Meier analysis was used to draw the survival curve according to different levels of cognitive function,and log-rank test was used for the homogeneity test of survival curve.The confounding factors of mortality were controlled by COX step-up regression and important confounding factors identified in previous studies.Cox regression was used to assess the impact of cognitive impairment and decline on all-cause mortality in the oldest old after controlling for potential confounding factors-including gender and agedemographic characteristics-and daily lifestyle factors.In a further subgroup analysisthe subgroup was stratified by age and sex.We use the stepwise regression in the COX model and important confounding factors identified in previous studies to control confounding factors,including gender and age,demographic characteristics(education status,occupation,marital status,living style,place of residence and activities of daily living)and daily lifestyle factors(exercise,current smoking,current drinking,housework,reading,watching TV,flower cultivation,and pastoral work).Cox regression was used to assess the impact of cognitive impairment and decline on all-cause mortality in the oldest old.In a further subgroup analysis,the subgroup was based on age(80-89 years,90 years and over)and gender(male and female)stratified the oldest old.ResultsIn the follow-up survey of this study from 1998 to 2014,a total of 28,896 theoldest old were included at baseline,with a mean age 92.85±7.49 years.The proportion of female elderly is much higher than that of male,accounting for 61.85%;The total number of follow-up years was 106820.99 and the total mortality accounted for 81.41%.After adjusting for confounders,firstly,according to the MMSE,cognitive function is divided into four cut-off points.When cognitive function is normal as a reference,moderate cognitive impairment,mild cognitive impairment,and severe cognitive impairment contribute to all-cause mortality.The hazard ratios were 1.07(1.02-1.11),1.18(1.14-1.23),and 1.42(1.36-1.47).After dividing cognitive function according to education level,cognitive impairment compared to normal cognitive function.The hazard ratio is 1.31(1.27-1.35).Secondly,in the study of cognitive decline on the risk of mortality for the oldest old,compared with the oldest old who have maintained normal cognitive function,the increased mortality risk by declined to severe cognitive impairment from normal cognitive function,moderate cognitive impairment and mild cognitive impairment were stronger,with hazard ratios 1.72(1.57-1.87),1.83(1.67-2.01),and 1.92(1.75-2.10),respectively.The hazard ratios of all-cause mortality were 1.16(1.07-1.25),1.30(1.20-1.41),and 1.76(1.63-1.89),respectively,for sustained moderate cognitive impairment,mild cognitive impairment,and severe cognitive impairment.Finally,in the subgroup analysis of the age and sex,cognitive impairment and decline have similar effects on all-cause mortality for the oldest old.The risk of all-cause mortality among the lower age groups of 80-89 years is higher than that of the oldest old aged ?90,and the results are statistically different;after gender stratification,we didn't find statistical difference.ConclusionThis study used a large prospective cohort study and found that cognitive impairment,taking into account education and cognitive decline,are important all-cause mortality for the oldest old.Cognitive decline has a greater impact onall-cause mortality than cognitive impairment.The research findings suggest that dynamic assessment of cognitive changes in elderly people,regular screening of cognitive impairment and cognitive decline in elderly people,and warning medical institutions and caregivers at all levels to strengthen protection of elderly patients with cognitive impairment and decline,to provide them with high-quality health services are of great significance for achieving healthy aging.