Cognitive impairment and mortality: a study of possible confounders

Dementia, cognitive impairment and mortality in persons aged 65 and over living in the community: a systematic review of the literature

BACKGROUND

No recent attempt has been made to synthesise information on mortality and dementia despite the theoretical and practical interest in the topic. Our objective was to estimate the influence on mortality of cognitive impairment and dementia.

METHODS

Data sources were Medline, Embase, personal files and colleagues' records. Studies were considered if they included a majority of persons aged 65 and over at baseline either drawn from a total community sample or drawn from a random sample from the community. Samples from health care facilities were excluded. The search located 68 community studies. Effect sizes were extracted from the studies and if they were not included in the published studies, effect sizes were calculated where possible: this was possible for 23 studies of cognitive impairment and 32 of dementia. No attempt was made to contact authors for missing data.

RESULTS

For the studies of cognitive impairment Fisher's method (a vote counting method), gave a p-value (from eight studies) of 0.00001. For studies of dementia, age-adjusted confidence intervals (CI) were pooled (odds ratio (OR) 2.63 with 95% CI 2.17 to 3.21 from six studies).

CONCLUSIONS

Levels of cognitive impairment commonly found in community studies give rise to an increased risk of mortality, and this appears to be true even for quite mild levels of impairment. The analysis confirms the increased risk of mortality for dementia, but reveals a dearth of information on the causes of the excess mortality and on possible effect modification by age, dementia subtype or other variables.

Cognitive impairment and mortality in older primary care patients

OBJECTIVE

To assess the impact of cognitive impairment on mortality in older primary care patients after controlling for confounding effects of demographic and comorbid chronic conditions.

DESIGN

Prospective cohort study.

SETTING

Academic primary care group practice.

PARTICIPANTS

Three thousand nine hundred and fifty-seven patients age 60 and older who completed the Short Portable Mental Status Questionnaire (SPMSQ) during routine office visits.

MEASUREMENTS

Cognitive impairment measured at baseline using the SPMSQ, demographics, problem drinking, history of smoking, clinical data (including weight, cholesterol level, and serum albumin), and comorbid chronic conditions collected at baseline; survival time measured during the 5 to 7 years after baseline.

RESULTS

Eight hundred and eighty-six patients (22.4%) died during the 5 to 7 years of follow-up. Cognitive impairment was categorized as having no impairment (84.3%), mild impairment (10.5%), and moderate-to-severe impairment (5.2%) based on SPMSQ score. Chi-square tests revealed that patients with moderate-to-severe impairment were significantly more likely to die compared with patients with mild impairment (40.8% vs 21.5%) and those with no impairment (40.8% vs 21.4%). No significant difference in crude mortality was found between patients with no impairment and those with mild impairment. After analyzing time to death using the Kaplan-Meier method, patients with moderate-to-severe cognitive impairment were at increased risk of death compared with those with no or mild impairment (Log-rank chi(2) = 55.5; P <.0001). Even in multivariable analyses using Cox proportional hazards to control for confounding factors, compared with those with no impairment, moderately-to-severely impaired patients had an increased risk of death, with a hazard ratio (HR) of 1.70. Increased risk of death was also associated with older age (HR = 1.03 for each year), a history of smoking (HR = 1.48), having a serum albumin level <3.5 g/L (HR = 1.29), and weighing less than 90% of the ideal body weight (HR = 1.98). Outpatient diagnoses associated with increased mortality risk were diabetes mellitus, coronary artery disease, congestive heart failure, cerebrovascular disease, cancer, anemia, and chronic obstructive pulmonary disease (HR range 1.36-1.67). Factors protective of mortality risk included female gender (HR = 0.67) and black race (HR = 0.73).

CONCLUSIONS

Moderate-to-severe cognitive impairment is associated with an increased risk of mortality, even after controlling for confounding effects of demographic and clinical characteristics. Mild cognitive impairment is not associated with mortality risk, but a longer follow-up period may be necessary to identify this risk if it exists.

Long-term predictors of cognitive outcome in a cohort of older people with hypertension

BACKGROUND

Deteriorating cognitive function in late life substantially increases the risk for dementia, for other non-cognitive morbidity, for dependency, and early death.

AIMS

To identify early predictors of late-life cognitive outcome.

METHOD

Cognitive function, premorbid IQ, and cardiovascular risk exposure were recorded on 1083 subjects on entry to a hypertension treatment trial in 1983-1984. We followed up this cohort 9-12 years later to assess cognitive function with the Mini-Mental State Examination (MMSE), to update exposure status, and to obtain genomic material. Multivariate analysis was used to identify independent baseline predictors of cognitive outcome 9-12 years later.

RESULTS

We followed up 387 subjects (58.6% of survivors). After adjusting for baseline cognition, poorer cognitive outcome was found to be independently associated with a family history of dementia, increasing age, less decline in systolic blood-pressure, lower premorbid IQ (rather than limited education), and abstinence from alcohol.

CONCLUSIONS

Reduction in systolic blood pressure (among hypertensives) and moderate alcohol intake could protect against cognitive deterioration in late life.

Smoking, drinking, and incident cognitive impairment: a cohort community based study included in the Gospel Oak project

OBJECTIVES

Recent longitudinal studies have reported that smoking increases risk for cognitive impairment and that moderate alcohol intake could be preventive. The association between both cigarette smoking and alcohol drinking and incident cognitive impairment was studied in a representative population.

METHODS

This is a 1 year prospective population based cohort study of all residents aged 65 or over in the electoral ward of Gospel Oak in London, UK (n=889). Cognitive impairment was assessed at baseline and 1 year later using the organic brain syndrome (OBS) cognitive impairment scale from the short CARE structured assessment. Subjects who were cognitively impaired at baseline were excluded from this analysis.

RESULTS

The prevalence of OBS cognitive impairment was 10.4% at index assessment and the 1 year cumulative incidence of cognitive impairment was 5.7%. Cognitive impairment was not associated with use of alcohol, although there was a non-significant association in the direction of a protective effect against onset of cognitive impairment for moderate drinkers compared with non-drinkers and heavy drinkers. Current smoking status predicted cognitive impairment (risk ratio (RR) 3.7; (95% confidence interval (95% CI)=1.1-12.3) independently from sex, age, alcohol, occupational class, education, handicap, depression, and baseline cognitive function.

CONCLUSIONS

Smoking seems to be a prospective risk factor for incident cognitive impairment; thus encouragement of older people to stop smoking could be considered as part of a strategy to reduce the incidence of cognitive impairment.

Survival effects in cognitive function, cognitive style, and sociodemographic variables in the Seattle Longitudinal Study

Survival effects in cognitive performance were examined in the Seattle Longitudinal Study (SLS) for a sample of 605 individuals who subsequently died (decedents) (n = 343 males; n = 262 females; M = 73.73 years of age) and a control group of 613 survivors (n = 299 males; n = 314 females; M = 71.91 years of age). A sample of survivors of similar age and have a similar level of education as the decedents was selected. Differences in cognitive functioning and cognitive style in level and change over time between decedents and survivors were studied. Decedents had lower levels of crystallized abilities (Verbal Meaning and Numerical Ability), visualization abilities (Spatial Orientation), verbal memory (Delayed Word Recall), perceptual speed (Identical Pictures), and Psychomotor Speed at last measurement. Decedents also had greater declines on Psychomotor Speed and Verbal Meaning at 7 and 14 years before the conclusion of the study. Survival effects were found to be ability-specific, appeared primarily in older adults, were more evident for males, and were observed up to 14 years before last measurement for specific abilities. Age-related changes in fluid ability appeared to be normative, whereas changes in crystallized abilities and perceptual speed may signify impending mortality.

Equivalence of two screens of cognitive functioning: the Short Portable Mental Status Questionnaire and the Orientation-Memory-Concentration test

OBJECTIVE

To determine the equivalence of two screens of cognitive functioning: the Short Portable Mental Status Questionnaire (SPMSQ) and the Orientation-Memory-Concentration (OMC) test.

DESIGN

The design was cross-sectional and longitudinal.

SETTING

Four rural and one urban county in the Piedmont region of North Carolina (n = 3210).

PARTICIPANTS

A stratified random cluster sample (n = 3210) of people 68 years of age and older.

MEASUREMENTS

SPMSQ and OMC at the fourth wave of the Duke Established Populations for Epidemiologic Studies of the Elderly (EPESE); disability, depression, and death measurements from the fourth through seventh waves of EPESE; demographic characteristics.

RESULTS

On the SPMSQ and the OMC (r = .80), 15.3% and 38.4%, respectively, of those tested were rated cognitively impaired. Poorer scores were associated with older age, black race, and less education. These associations were attenuated on the dichotomized SPMSQ but not on the OMC. Both measures predicted disability and depressive symptomatology currently and 3 years hence and death.

CONCLUSIONS

The SPMSQ and OMC, although highly correlated, are not equivalent. Association with race and education are greater for the OMC, whereas an association with age exists for both measures. The milder level of impairment identified by the OMC increases predictive capacity.

Factors associated with six-month mortality in recipients of community-based long-term care

OBJECTIVES

To determine factors associated with short-term mortality in recipients of community-based long-term care (CBLTC).

DESIGN

A cohort study.

SETTING

A Medicaid home- and community-based waiver and state-funded homecare program.

PARTICIPANTS

All persons age 65 and older newly admitted to the program from January 1, 1988, to March 31, 1991.

MEASUREMENTS

Demographics, functional, cognitive, and health status, depression, and social support were obtained in an admission assessment. Six-month mortality data were obtained by linking assessment data to a state mortality registry.

RESULTS

There were 718 deaths among 6784 CBLTC clients. Male sex (AOR 1.8, 95% CI 1.5-2.1), the presence of cancer (AOR 3.2, CI 2.6-3.9), heart disease (AOR 1.3, CI 1.1-1.5), chronic obstructive pulmonary disease (AOR 1.8, CI 1.4-2.2), or nutritional problems (AOR 1.7, CI 1.4-2.0), functional impairment (AOR for lowest compared to highest quartile 2.9, CI 2.0-4.1), severe cognitive impairment (AOR 1.6, CI 1.3-2.1), self-assessment of health as poor (AOR 1.5, CI 1.1-2.0), feeling depressed (AOR 1.2, CI 1.1-1.3), and hospitalization (AOR 2.7, CI 2.2-3.2) were independently associated with 6-month mortality in bivariate and multivariate analyses.

CONCLUSIONS

Clinical data obtained during routine assessment of CBLTC clients can be used to assess short-term mortality. Six-month mortality is associated with poor functional and cognitive status, the presence of cancer, heart disease, COPD, and nutritional problems, depression, perception of poor health, and hospitalization.

Disability and cognitive impairment in the elderly

Disability and cognitive impairment show similar patterns of increasing frequency with ageing. A review of the published literature shows that there is a cross-sectional relationship between cognitive impairment and disability, independent of demographic, medical, and lifestyle factors. Some instrumental activities of daily living (IADL) items appear more specifically related to cognitive impairment, but cognition and functional impairment are distinct concepts requiring separate assessments. Subjects with low cognitive performances are at higher risk of functional impairment in the following years. Cognitive impairment as well as disability increase the risk of death and institutionalization. Preventive strategies could be directed against the risk factors of cognitive impairment and disability, and would aim to delay the onset of dementia. Prevention of disability associated with cognitive impairment needs further assessment in elderly community-dwellers. Further research is needed to better identify the specific areas cognition involved in the disablement process.

Low blood pressure and five-year mortality in a Stockholm cohort of the very old: possible confounding by cognitive impairment and other factors

OBJECTIVES

Low blood pressure has often been reported to be related to excess mortality in people over the age of 75 years. This study examined whether other predictors may account for the association.

METHODS

A community-based cohort of 1810 people who were aged 75 years and older was followed for 5 years.

RESULTS

The relative risk of death was 1.39 (95% confidence interval [CI] = 1.11, 1.73) for people with systolic pressure lower than 130 mm Hg and 1.21 (95% CI = 1.02, 1.43) for those with diastolic pressure lower than 75 mm Hg, compared with corresponding reference groups, when all other variables were simultaneously considered in Cox proportional hazards models. The observed association was present mainly in subjects with at least two of the three conditions (cardiovascular disease, limitation in activities of daily living, or cognitive impairment). The effect of low diastolic pressure on mortality was also significant in those with only cognitive impairment.

CONCLUSIONS

Preexisting cardiovascular disease, limitation in activities of daily living, and, more important, cognitive impairment may be responsible for the association of low blood pressure with increased mortality in the very old in that they cause both reductions in blood pressure and excess deaths.

A longitudinal study of factors predicting change in cognitive test scores over time, in an older hypertensive population

This study aims to describe factors associated with cognitive decline among 2584 subjects, aged 65-74, who were followed up for 54 months in the Medical Research Council Elderly Hypertension Trial (1982-1989). The subjects completed a cognitive test, the Paired Associate Learning Test (PALT), five times over this period. Decline on the PALT was associated with advanced age, male sex, rural residence, depression and low intelligence. These effects were modified by gender and level of pre-morbid intelligence. Advanced age, rural residence and number of cigarettes smoked daily were only associated with PALT decline among women of below median intelligence. The association between depression and PALT decline was only apparent in women of below median intelligence and men of above median intelligence. While these findings are consistent with other research into cognitive decline, they differ in some ways from reported risk factors for dementia, suggesting aetiological separateness. That women were more vulnerable than men to the effects of age and smoking raises the question of the impact on cognition of accelerated atherosclerosis after the menopause.

Cognitive impairment and mortality in a cohort of elderly people

OBJECTIVES

To investigate the relation between cognitive function and cause specific mortality in people aged 65 and over. DESIGN-A 20 year follow up study of a cohort of randomly selected elderly people living in the community who in 1973-4 had taken part in a nutritional survey funded by the Department of Health and Social Security.

SETTING

Eight areas in Britain (five in England, two in Scotland, and one in Wales).

SUBJECTS

921 men and women whose cognitive function was assessed by a geriatrician in 1973-4 and for whom data on health, socioeconomic circumstances, and diet had been recorded.

RESULTS

Cognitive impairment was associated with increased mortality, in particular death from ischaemic stroke. Those who scored 7 or less on the Hodkinson mental test had a relative risk of dying from stroke of 2.8 (95% confidence interval 1.4 to 5.5), compared with those who gained the maximum score (10), after adjustment for age, sex, blood pressure, serum cholesterol concentration, and vitamin C intake. These associations were independent of illness or social class. At the time of the nutritional survey, cognitive function was poorest in those with the lowest vitamin C status, whether measured by dietary intake or plasma ascorbic acid concentration. The relation between vitamin C status and cognitive function was independent of age, illness, social class, or other dietary variables.

CONCLUSION

The relation between cognitive function and risk of death from stroke suggests that cerebrovascular disease is an important cause of declining cognitive function. Vitamin C status may be a determinant of cognitive function in elderly people through its effect on atherogenesis. A high vitamin C intake may protect against both cognitive impairment and cerebrovascular disease.

Cognitive impairment and mortality in older community residents

OBJECTIVE

Cognitive impairment among the elderly has been linked to mortality in studies of clinical populations. The purpose of this study was to examine the mortality risk associated with cognitive impairment among elderly populations in the community.

METHODS

Cognitive impairment and other social and health factors were assessed in 1855 elderly community residents. This sample was reinterviewed periodically to assess changes in health and survival.

RESULTS

At baseline 33% of the sample were mildly impaired and 8% were severely impaired. Across a 48-month observation period the survival probability was .85 for the cognitively unimpaired, .69 for the mildly impaired, and .51 for severely impaired respondents. When adjustments were made for the effects of other health and social covariates, severely impaired persons were twice as likely to die as unimpaired persons. Those who were mildly impaired were also at an increased risk.

CONCLUSIONS

Other investigators have found that cognitive impairment is a significant predictor of dementia. We found that it is a significant predictor of mortality as well. Early detection of impaired cognition and attention to associated health problems could improve the quality of life of these older adults and perhaps extend their survival.

Cognitive deficits related to major organ failure: the potential role of neuropsychological testing

Until recently, little attention has been paid to the possibility of cognitive deficits in patients with disease or failure of major organs such as the liver, kidney, or heart. However, there is a growing awareness that major organ failure often has neuropsychological sequelae. These sequelae may at times be quite subtle and not detectable under gross examination. Nevertheless, even subtle deficits may have a major impact on adherence to medical regimens, psychosocial adjustment, and quality of life of patients. Neuropsychological assessment has a potentially valuable role to play both in research and in clinical work. It can be useful in adding to our knowledge of the cognitive effects of various types, severity and duration of major organ disease, as well as sequelae associated with treatment. It also is a potentially valuable clinical tool for identifying cognitive deficits that will affect the quality of life and probability of survival for organ failure patients.

The Timed Manual Performance test as a predictor of hospitalization and death in a community-based elderly population

OBJECTIVE

To determine the usefulness of timed manual performance measurements (TMP) as predictors of health outcomes, hospitalization, and mortality in a large, heterogeneous sample of elderly people living in the community.

DESIGN

Prospective cohort study.

SETTING

Central North Carolina.

PARTICIPANTS

1,286 community-dwelling older people.

MEASUREMENTS

Demographic background, health problems, number of prescribed medications, perceived health, quality of life, and the TMP, a 27-item test that has been shown to predict functional dependency and need of health-care services in older people.

RESULTS

During the 2-year follow-up period, 127 people died and 200 were hospitalized. Scores for those who were able to complete the original TMP, as well as scores for two shorter versions of the TMP, predicted mortality and, to a lesser extent, hospitalization within 2 years. For both original and shorter versions of the TMP, relative risk of death was approximately 2.5 times greater for those in the poorest performance quartile, as compared with the best performing quartile, when adjusted for age, gender, race, and number of prescribed medications. TMP tests and an index of IADL were independent predictors of death.

CONCLUSIONS

TMP scores may be useful in the clinical setting as a vital sign of functioning, providing a means of targeting those individuals at increased risk of mortality.

Cognitive impairment and the use of health services in an elderly rural population: the MoVIES project. Monongahela Valley Independent Elders Survey

OBJECTIVE

To describe the patterns of use of health and human services by elderly rural individuals and to determine whether cognitively impaired persons had a distinctive pattern of service utilization.

DESIGN

An epidemiological survey and cognitive screening of an age-stratified random community sample.

SETTING

The mid-Monongahela Valley, a rural community in Southwestern Pennsylvania.

PARTICIPANTS

1366 non-institutionalized persons aged 65 years and older, fluent in English, and with at least a sixth grade education.

MEASUREMENTS

We administered a battery of cognitive screening tests (the Mini-Mental State Examination; Immediate and Delayed Recall of a Story; Immediate and Delayed Recall of a Word List; CERAD modification of the Boston Naming Test; Verbal Fluency for initial letters P and S and for names of Fruits and Animals; Temporal Orientation; Praxis; Clock Drawing; and Trailmaking Tests A and B.) We also obtained basic demographic information and inquired about the use of health and human services in the previous year.

RESULTS

Approximately 10% of the sample was classified (by operational criteria) as cognitively impaired. In univariate analyses, cognitive impairment was found to be significantly associated with the use of certain health services: hospitalization in the previous 6 months (odds ratio, OR = 2.1; 95% CI = 1.3, 3.3), previous nursing home use (OR = 9.3; 95% CI = 3.8, 22.9), home health care (OR = 4.6; 95% CI = 2.7, 8.0), social services (OR = 6.5; 95% CI = 3.4, 12.4), mental health services (OR = 2.8; 95% CI = 1.2, 6.2), and the regular use of prescription medications (OR = 2.0; 95% CI = 1.3, 3.2). Visits to physicians were not significantly different between the impaired and unimpaired groups. In a multiple regression model, which included age and educational level, the use of home health care (OR = 3.4; 95% CI = 1.8, 6.4) and social services (OR = 2.3; 95% CI = 1.1, 4.9) remained significantly associated with cognitive impairment.

CONCLUSIONS

The association of cognitive impairment with the use of these health and human services underscores the general frailty of the impaired group. These findings also point to potential target groups in the community for further evaluation and services for dementia. The findings support the need for education regarding cognitive impairment and dementia to be made available to providers of these services, particularly informal social services such as those provided by church groups.